There are 135 participants who submitted an abstract.
Name: Adams, Betsey
Talk/Poster: Talk
Title: The edges of galaxy formation as revealed by neutral hydrogen surveys
Abstract:
Neutral hydrogen (HI) surveys offer a unique view into galaxy evolution and formation, identifying galaxies based on their gas reservoir and potential for star formation. The current and upcoming generations of neutral hydrogen surveys have the sensitivity to detect rare but extremely important objects that represent the extreme limits of systems that
are able to form stars. The ALFALFA HI survey paved the way in these studies, and in the near future Apertif will build on this work, offering a detailed view of the neutral hydrogen in these extreme galaxies. I will highlight current results from ALFALFA: the discovery of the most marginal galaxies, identified as ultra-compact high velocity clouds, the identification of field gas-rich ultra-diffuse galaxies, and results from the SHIELD sample of low-mass dwarf galaxies. Most of these results required further follow-up with interferometric observations to constrain the HI distribution. Apertif will offer resolved HI data immediately, offering a powerful new window into these galaxies on the edge of formation. |
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Name: Aerts, Conny
Talk/Poster: Talk
Title: Asteroseismology at the service of Astrophysics
Abstract:
After a basic introduction into asteroseismology, we show how
detected and identified oscillation modes from uninterrupted time-series space
photometry allow to deduce properties of stellar interiors that are impossible
to unravel from snapshot data. We reveal the power of combining Gaia and
asteroseismic data for galactic archeology and for exoplanet studies. A major
achievement of the Kepler mission is that it initiated gravity-mode
asteroseismology. We show how this sub-branch allows to determine the interior
rotation frequency and chemical mixing in the near-core regions of massive
stars, revolutionising our view on angular momentum of stars. We end by
highlighting future prospects based on new dedicated space photometry coming up
with the TESS and PLATO missions, in combination with astrometry from Gaia and
dedicated ground-based spectroscopy. |
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Name: AL-Zetoun, Ala'a
Talk/Poster: Poster
Title: More realistic propagation of cosmic rays
Abstract:
I will show a simple diffusion model for the galactic magnetic field to follow cosmic ray particles in galaxy. By using a numerical solution method (Itô equation) based on stochastic differential equation, taking into account of anisotropic diffusion. Show the result of this model; the path length distribution, the grammage distribution, and the residence time. |
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Name: Aranzana, Ester
Talk/Poster: Talk
Title: High frequency optical variability properties of the largest AGN sample observed with Kepler/K2
Abstract:
We present the first high-frequency optical variability study of a large sample
of Active Galactic Nuclei (AGN) observed with the Kepler/K2 mission. The
sample contains 276 AGN observed over four campaigns with 30-minute cadence
selected from the Million Quasar Catalogue with an R magnitude < 19.
We performed time series analysis to determine their variability properties by
means of the power spectral densities (PSDs) and applied Monte Carlo techniques
to find the best model parameters that fit the observed power spectra.
A power-law model is sufficient to describe 90 % of the AGN, the other 10 %
present bumps and dips deviating significantly from the simple model. The
average power-law slope is 2.5±0.5, steeper than the PSDs observed in X-rays,
and the rest-frame amplitude variability ranges from 1−10 % with an average
of 2.5 %. We explore correlations between the variability amplitude and parameters
such as redshift, magnitude, and black-hole mass. This study also enables
us to distinguish between Seyferts and blazars and confirm AGN candidates.
The steep PSDs observed are inconsistent with the damped random walk model
suggesting a different physical mechanism generating the fast variability. |
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Name: Arcangeli, Jacob
Talk/Poster: Talk
Title: Climate of Hot Jupiters: spectroscopic phase-curve of the exoplanet WASP-18b with HST.
Abstract:
Measuring the atmospheric composition and structure of a range of planets to constrain planetary formation is an important goal in exoplanetology. Towards this goal ongoing surveys target the brightest stars, and find very hot-Jupiters with temperatures greater than 2000K. However, studies have shown that the most irradiated planets appear to have isothermal day-side spectra in the NIR, thus no longer exhibit spectral features which are crucially needed to study their atmospheres in detail.
We present new results that demonstrate that the atmospheric characteristics of the hottest planets can indeed be retrieved. We illustrate this through phase-curves studies of the very hottest planets observed with HST/WFC3. Our results suggest that hot-Jupiters are separated into different classes depending on their thermal structure. Our findings make the extremely irradiated Hot-Jupiters very compelling candidates to learn about their composition with JWST. |
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Name: Archibald, Anne
Talk/Poster: Poster
Title: Testing Gravity with the Pulsar Triple System: Getting the Most out of Timing Data
Abstract:
PSR J0337+1715 is a millisecond pulsar in a hierarchical triple. This unique system permits a very strong test of the Equivalence Principle: does the pulsar's binding energy fall the same way as rest mass? Obtaining believable results from this test requires precision timing data. In particular we must understand and mitigate effects such as polarization calibration, scintillation, and intrinsic profile variation. We discuss these phenomena and how to mitigate their effects. Our results may well be applicable to other applications of precision pulsar timing, including attempts to detect gravitational waves with a pulsar timing array. |
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Name: Barber, Christopher
Talk/Poster: Talk
Title: The Effect of a Variable IMF on Galaxy Properties in the EAGLE Simulations
Abstract:
Recent observations have found evidence that the stellar initial mass function (IMF), once thought to be universal, may vary with stellar velocity dispersion in local massive elliptical galaxies. It is, however, unclear what implications such IMF variations may have on galaxy properties, as current state-of-the-art cosmological simulations typically assume a universal IMF. We present a new cosmological hydrodynamical simulation based on the EAGLE simulation suite that self-consistently includes an IMF that varies on a per-particle basis as a function of local pressure of star-forming gas particles. We show that such a variation can reproduce the observed trends of increasing bottom-heaviness with central stellar velocity dispersion, and predicts the recently observed radial IMF gradients within high-mass early-type galaxies. However, for galaxies with stellar mass > 10^10 Msun, such an IMF variation merkedly alters the alpha-to-iron abundance ratio and produces galaxies with 0.3 dex higher stellar mass than the reference run with a fixed Chabrier IMF. We caution that assuming a Chabrier IMF when converting light to mass in galaxies with our intrinsically variable IMF may cause underpredictions of the true stellar mass by up to a factor of 2. |
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Name: Boersma, Oliver
Talk/Poster: Poster
Title: The gravitational-wave memory effect.
Abstract:
The two gravitational-wave (GW) detections by the LIGO-Virgo collaboration have begun an era of testing strong-field gravitational effects.
Many predictions of general relativity have held up so far.
One unusual nonlinear effect in the gravitational waveform that has evaded measurement as of yet is the GW memory effect.
As Lasky et al. showed, the signal-to-noise ratio of the memory for an event like the first detection (GW150914) is too small to claim detection.
They, however, proposed a way of coherently adding the memory signals from multiple detections to produce significant evidence for the memory.
Lasky et al. performed a proof-of-principle study, which had certain limitations.
Notably, they considered an ensemble of binary black holes (BBHs) just like GW150914. On this poster, I will give an overview of their work and of how I plan to extend their results by considering a more realistic BBH population. |
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Name: Bollen, Dylan
Talk/Poster: Poster
Title: Jet launching revealed in post-AGB binaries
Abstract:
Binary interaction processes are believed to be the main shaping agent of asymmetric Planetary Nebulae (PNe).
The binary interactions induce jet formation, which is at the origin of the nonspherical structures we observe in PNe. Our current observations show that these jets are also common in the PN-progenitors, namely post-AGB binaries.
In this talk, we provide the results of our quantitative study on the origin and properties of high-velocity outflows in post-AGB binaries. We present the analyses of line-profile variability, based on our long-term monitoring of post-AGB binaries with the high-resolution spectrograph HERMES mounted on the 1.2m Mercator telescope. We deduced the jet geometry by comparing orbital phased data and our jet model. We show that the systems are the result of a binary interaction channel, in which the gaseous circumcompanion disk is the origin of the fast outflow. These quantitative analyses provide us with the necessary data in order to model binary PNe. We show that the mechanism of jet production is very commonly observed among post-AGB binaries. Our ultimate goal is to study the impact of these jets onto the evolution of these systems. |
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Name: Boulangier, Jels
Talk/Poster: Poster
Title: Self-consistent hydro-chemical model for shocked stellar winds
Abstract:
Mass loss from evolved stars, such as AGB stars, are one of the most dominant sources of chemical enrichment of the ISM. The chemical mixture of the ISM eventually determines the composition of molecular clouds, stars and even planets. As stars evolve, almost all of them go through the AGB phase and the chemical life cycle is complete. Understanding the transport by and composition of the AGB stellar winds, from the star itself to the ISM, is a crucial stage in the cycle. The physical and chemical conditions of AGB winds, which contain shocks, are poorly understood due to i) lack of high resolution observations, ii) simplifying assumptions in theoretical models and iii) lack of laboratory data. We strive towards developing a self-consistent hydro-chemical model, improving on the current wind models. This approach is needed because of the intricate interplay between dynamics and chemistry, caused by shocks and cooling/heating. The chemical composition determines which cooling mechanisms (e.g. H2, CO, metal lines) influence the thermal evolution of the gas. In turn, the temperature acts on the dynamical behaviour of the wind which again will impact the rate of chemical reactions. Therefore, we take into account all important chemical reactions and thermal mechanisms. A future prospect is to include dust, aiming for a more complete picture of dust-driven AGB winds. Our self-consistent hydro-chemical model will help us answering questions such as: What is the dynamical/chemical structure in AGB winds? How important is the chemical-dynamical feedback loop? Do chemical instabilities exist? |
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Name: Breddels, Maarten
Talk/Poster: Talk
Title: A billion stars in the Jupyter Notebook
Abstract:
With large astronomical catalogues containing more than a billion stars becoming common, such as from Gaia, we are preparing for methods to visualize and explore these large datasets. Data volumes of this size requires different visualization techniques, since scatter plots become too slow and meaningless due to overplotting. We solve the performance and visualization issue using binned statistics, e.g. histograms, density maps, and volume rendering in 3d. The calculation of statistics on N-dimensional grids is handled by Python library called vaex, which I will introduce. It can process at least a billion samples per second, to produce for instance the mean of a quantity on a regular grid. This statistics can be calculated for any mathematical expression on the data (numpy style) and can be on the full dataset or subsets, specified by queries/selections.
However, to visualize higher dimensional data in the notebook interactively, no proper solution existed. This led to the development of ipyvolume, which can render 3d volumes and up to a million glyphs (scatter plots and quiver) in the Jupyter notebook as a widget. With the browser as a platform, and the release of ipywidgets 6.0, these 3d plots can also be embedded in static html files and renders on nbviewer. This allows for sharing with colleagues, rendering on your tablet (paperless office), outreach, press release material, etc. Overlaying 3d quiver plots on a 3d volume rendering allows exploring a 6d (or higher) space. |
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Name: Bremer, Jonas
Talk/Poster: Poster
Title: The effect of warm dark matter on the metal enrichment of the intergalacitc medium
Abstract:
Aside the success of the LCDM paradigm in explaining the formation of structure, the large scale matter distribution in the universe, the Lyman alpha forest and the temperature anisotropies in the CMB, it is unable to predict the observed formation of structure on sub-galactic scales. Various solutions of different nature have been considered in order to resolve the small scale crisis. Besides solutions that rely on baryonic physics, modifications to the nature of dark mater have been proposed. One of these candidates is Warm Dark Matter (WDM) that consists of relativistic thermally decoupled particles with a mass of several keV. As a consequence, free-streaming of WDM particles suppresses power to an extent and on a scale that is set by the WDM particle mass. This results in a suppression of dark matter halos below 1e9.5 solar mass. As these low mass halos are effective at polluting the
intergalactic medium (IGM) with metals, one expects that at high redshift the IGM is more metal rich in CDM as compared to WDM.
In this work, the effect of three WDM cosmologies on the metal enrichment of the IGM is investigated, namely WDM with 1.5,3 and 5 keV particle masses. We track the amount of metals in the universe using a semi-analytical model. As the abundance of metals in the IGM is highly uncertain at z = 5-6 and unknown for larger redshifts, this could provide a testbed to distinguish between CDM and WDM. |
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Name: Brienza, Marisa
Talk/Poster: Talk
Title: The story of the restarted radio galaxy B2 0258+35
Abstract:
Radio galaxies are episodic in nature, cycling through periods of activity and quiescence. Evidence of this recurrence is observed in restarted radio galaxies where large-scale old plasma is seen together with a pair of newborn jets. These sources provide a unique opportunity to study the duty-cycle of radio jets in AGN.
In this talk I will present the intriguing story of the radio source B2 0258+35. This source shows a compact two-lobe morphology of ~1 kpc size with an age of 0.9 Myr. On a large scale, two low surface brightness lobe structures have been detected at 1.4 GHz using the WSRT, extending to a total size of 240 kpc. These large-scale lobes were interpreted as an evidence of a previous cycle of jet activity.
Using complementary data at 150 MHz, 330 MHz and 6 GHz obtained with LOFAR, VLA and SRT respectively, we have investigated the nature of the extended lobes. Unexpectedly, the radio spectrum doesn't show the typical steepening at high frequency that is characteristic of remnant ageing plasma. Moreover, all observations show an enhancement in surface brightness along one edge of each lobe suggesting the jets may have been precessing before switching off. This may support the idea that instabilities in the accretion process have dictated the switch off/on of the jets.
To conclude I will present our search in the LOTSS survey for extended emission around young, compact radio galaxies to provide better statistics on their presence and properties. |
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Name: Brinkerink, Christiaan
Talk/Poster: Talk
Title: NCLE: a fast track towards space-based low-frequency radio astronomy
Abstract:
Radboud Radio Lab, together with partners ASTRON and Innovative Solutions in Space (ISIS), is currently developing NCLE (Netherlands-China Low frequency Explorer) - an instrument that will perform low-frequency radio astronomy from the Earth-Moon L2 point. The instrument will fly on the Chinese Chang'e 4 mission, to be launched in 2018. The science band ranges from 80 kHz to 80 MHz, covering diverse science goals such as Solar bursts, Earth RFI studies, planetary magnetosphere emission and low-frequency transient detection. NCLE will also attempt, for the first time, to constrain the emission from the Epoch of Reionization - paving the way for a future space-based or lunar low frequency interferometer. In this talk, I will present these science cases and the way in which we use off-the-shelf components for rapid development of a space-worthy scientific instrument. |
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Name: Brinkman, Hannah
Talk/Poster: Poster
Title: Electron-capture supernovae in binaries
Abstract:
Electron-capture supernovae are considered to be the source of low-kick neutron stars. However, it is not clear how many of these supernova events occur, and how many of them occur in binary systems. To find an answer to this question, I have simulated a grid of binary stars with MESA to find the possible progenitor systems of electron-capture supernovae. My research focusses on the primary star of the binary before any reverse mass-transfer can occur, and if this star can become an electron-capture supernova.
When the parameter space for electron-capture supernovae in binaries is known, it is possible to make a prediction on how often systems like these occur, and subsequently estimate the supernova rate expected from these systems.
By the time of the conference I hope to have all the results of the research. |
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Name: Broderick, Jess
Talk/Poster: Talk
Title: MANTIS: The Mid-Frequency Aperture Array Transient and Intensity-Mapping System
Abstract:
Aperture arrays are very flexible systems that are ideal for cutting-edge investigations in radio astronomy (e.g. LOFAR, a key Dutch facility). ASTRON is leading the design consortium for a proposed third component of the full Square Kilometre Array (SKA): a mid-frequency aperture array (MFAA), operating between 450-1450 MHz. The MFAA has the immense potential to do the lion's share of transformational SKA science.
MANTIS, the Mid-Frequency Aperture Array Transient and Intensity-Mapping System, is the proposed precursor of the full MFAA. With more than 1500 m^2 of collecting area and an extremely wide field of view (>100 deg^2), MANTIS will be a powerful telescope in its own right, capable of unique science as well as being an essential technology demonstrator. Firstly, it will be a powerful probe of the dynamic radio sky, helping, for example, to significantly improve the statistics of fast radio bursts (FRBs). Cosmological HI surveys using the intensity mapping (IM) technique will map the baryon acoustic oscillation (BAO) signature out to intermediate redshifts, yielding new clues on the nature of dark energy. Furthermore, unique pulsar timing experiments will be possible due to large increases in on-source time, and there will be significant potential for a range of other wide-field searches and surveys: SETI, diffuse synchrotron emission, and the faint end of the HI mass function.
In this talk, I will provide an overview of the planned MANTIS telescope, and also show highlights from its forerunner, the Electronic Multi-Beam Radio Astronomy ConcEpt (EMBRACE), that is currently operational. |
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Name: Bronzwaer, Thomas
Talk/Poster: Talk
Title: RAPTOR: A Public Code for Time-dependent Radiative Transfer in Arbitrary Spacetimes
Abstract:
We present RAPTOR, a new, public code that is capable of numerically integrating the equations of motion of light rays and of solving the radiative transfer equation in arbitrary (analytical or numerical) spacetimes. Key features of RAPTOR include time-dependent radiative transfer, relaxing the assumption of a static plasma during transfer calculations, and the fact that it is a hybrid code that can be run on both CPU’s and GPU’s. RAPTOR also supports non-thermal particle distributions and is VR-compatible. We apply RAPTOR to the study of radiative transfer around black holes, focusing on examining the difference between the approximate ``fast light" paradigm, in which light moves at infinite speed, and the physically correct ``slow light" paradigm, in which the light's motion is taken into account while producing images and light curves. We find that in our accretion flow model, the fast light simulation results are a good approximation of the slow light simulation results. |
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Name: Burns, Ross
Talk/Poster: Talk
Title: Massive star formation using maser VLBI
Abstract:
Massive stars form in deeply embedded gas cores, often at great distances from us, making it almost impossible to observe them directly. In this contribution I present the use of maser VLBI as an observational tool for tracing the 3D motions of powerful jets which are launched from the disks of accreting massive stars. These jets, in turn, reveal the history of accretion cycles of massive stars - a key component in solving the mystery of their formation. |
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Name: Burtscher, Leo
Talk/Poster: Talk
Title: The multi-scale, multi-wavelength view of obscuration in local AGNs
Abstract:
We present the obscuration and dust emission properties of a sample of local AGNs and show that they can be brought together to form a consistent view of the nuclear obscuring material. This picture includes near- and mid-infrared interferometry, resolving the hot and warm dust structures, as well as obscuration measures based on adaptive-optics assisted IFU observations yielding the near-infrared color temperature and the dilution of stellar absorption lines. We also derive the obscuration towards the broad line region while at the same time fitting its density and ionizing flux from the simultaneous observation of multiple broad Balmer lines using UV-to-near-infrared VLT/X-SHOOTER spectroscopy. Finally, we combine these optical and infrared obscuration estimates with the X-ray absorption properties derived using 0.3-150 keV spectral energy distributions and dissect the absorbing column into the dusty and dust-free parts of the nucleus. |
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Name: Cai, Maxwell Xu
Talk/Poster: Poster
Title: Stability of multiplanetary systems in star clusters
Abstract:
Most stars, if not all, are formed in star clusters. Planet formation is a quick (a few Myr) process following the star formation. While more than 3000 planetary systems are discovered so far, most of them are in the Galactic field; only less than 1% of them are found in star clusters. We explore this dichotomy by studying the dynamical stability of multiplanetary systems in star clusters using direct N-body simulations. Three different star cluster models with respectively N = 2k, 8k, and 32k stars are used as the host environments. In the host cluster, solar-type stars are considered as host stars and are assigned with multiplanetary systems. I would be delighted to present a stability study of these systems during the conference. |
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Name: Callingham, Joseph
Talk/Poster: Talk
Title: Dying young and frustrated? A low radio frequency view of young radio galaxies
Abstract:
Many active galactic nuclei (AGN) show a peak or turnover in their radio spectrum. Peaked-spectrum radio sources (including gigahertz-peaked spectrum and compact steep spectrum sources) are all radio galaxies with small angular extents, suggesting that they are either very young AGN or are confined by a dense surrounding medium. We here present a spectacular sample of 1484 low-frequency peaked-spectrum sources derived from the Murchison Widefield Array's GLEAM survey; for 95% of this sample, the peaked spectral behaviour is newly identified. This very large sample allows us to perform a comprehensive study of the properties of peaked-spectrum sources as a function of luminosity and redshift. We also identify six sources that have optically thick spectral indices that are near or above the synchrotron self-absorption (SSA) limit, which could represent the first peaked-spectrum sources in violation of SSA theory. This talk will concluded with what LOFAR Multifrequency Snapshot Survey (MSSS) can achieve in this area. |
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Name: Ceccobello, Chiara
Talk/Poster: Poster
Title: Self-similar semi-analytical RMHD jet model
Abstract:
Jets are ubiquitous and reveal themselves at different scales and redshifts, showing an extreme diversity in energetics, shapes and emission. Indeed jets are found to be characteristic features of black hole systems, such as X-ray binaries (XRBs) and active galactic nuclei (AGN), as well as of young stellar objects (YSOs) and gamma-ray bursts (GRBs).
Observations suggest that jets are an energetically important component of the system that host them, because the jet power appears to be comparable to the accretion power.
Significant evidence has been found of the impact of jets not only in the immediate proximity of the central object, but as well on their surrounding environment, where they deposit the energy extracted from the accretion flow. Moreover, the inflow/outflow system produces radiation over the entire electromagnetic spectrum, from radio to X-rays. Therefore it is a compelling problem to be solved and deeply understood.
I will present a new integration scheme to solve radial self-similar, stationary, axisymmetric relativistic magneto-hydro-dynamics (MHD) equations describing collimated, relativistic outflows crossing smoothly all the singular points (the Alfven point and the modified slow/fast points).
For the first time, the integration can be performed all the way from the disk mid-plane to downstream of the modified fast point, where there are hints of a shock.
I will discuss an ensemble of jet solutions showing diverse jet dynamics (jet Lorentz factor ~ 1-10) and geometric properties (i.e. shock height ~ 10^3 - 10^7 Rg), which makes our model suitable for application to many different systems where a relativistic jet is launched. |
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Name: Chambers, Frank
Talk/Poster: Poster
Title: Superburst Oscillations
Abstract:
Superbursts are hours long X-Ray bursts with long recurrence times that are observed from accreting Neutron Stars. They are believed to be caused by unstable thermonuclear burning of carbon deep in the ocean at densities approximately 10^8 - 10^9 g cm^3 and can be triggered by even a small fraction of carbon given a sufficiently large mass of ashes. The burning is affected strongly by ash composition so these burst are a good probe of nuclear burning processes.
Burst oscillations have been discovered during some superbursts, which could plausibly be caused by some form of surface mode. We present calculations of modes in the aftermath of a superburst, in a similar approach to Piro and Bildsten's 2005 work on modes in H/He burning oceans after normal Type I Bursts. |
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Name: Chatterjee, Koushik
Talk/Poster: Poster
Title: Probing Large Scale Relativistic Jets and their Magnetic Fields
Abstract:
For several years, understanding the effects of the magnetic field on the acceleration profile of relativistic jets has been a major area of research. Previously, we were hindered by the lack of sufficient computing power to accurately evolve these jets over large time-scales. Using H-AMR, a high-performance GPU-based general relativistic magnetohydrodynamic (GR-MHD) code, we can now probe jet features more than 5 orders of magnitude in distance away from the event horizon. This allows the study of the general dependence of jet properties on the accretion of magnetic flux by the black hole, which is relevant for observational predictions. Another feature of these powerful jets are shocks-like processes which, theoretically, are able to explain the acceleration of particles inside the jet to high velocities. These shocks have been proposed to form at regions where causal connection between the jet and the black hole is broken. I will present the results of new axisymmetric GR-MHD simulations where we explore the physical nature of the jet after it achieves a relatively steady state, describing trends between properties such as the lorentz factor, the electro-magnetic energy and the location of these “break” regions. |
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Name: Concha Ramírez, Francisca
Talk/Poster: Poster
Title: Viscous evolution of circumstellar disks in young star clusters
Abstract:
Stars with circumstellar disks form in environments high in stellar and gas densities, which affects disks through processes such as truncation from dynamical interactions, ram pressure stripping, and external photoevaporation. Circumstellar disks also undergo internal viscous evolution, leading to disk expansion and mass accretion onto the central star.
Previous work indicates that dynamical truncation and viscous evolution play a major role in determining circumstellar disk size and mass distributions. However, it remains unclear under what circumstances which of these two processes dominates.
We present results of simulations of young clusters taking into account dynamical interaction between stars and viscous evolution of disks. Coupling viscous disk evolution with direct N-body code is done using the AMUSE framework. Cluster gas presence is modeled as a time variable background potential. We compare these results with actual observations of size, mass, and accretion rates of circumstellar disks inside star clusters.
We argue that the relative importance of dynamical truncation and the disks' viscous evolution changes with time and cluster density. Viscous evolution makes the importance of dynamical encounters increase with time. Gas presence results in more dynamical encounters, compared to simulations without gas. Gas expulsion causes the cluster to expand, making the moment of gas expulsion a critical variable in the importance of dynamical truncation.
Simulation results for disk masses and accretion rates are in agreement with observations of the Trapezium cluster. Disk sizes are overestimated by our model, suggesting the need to include other physical processes that might be triggering disk truncation. |
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Name: Connor, Liam
Talk/Poster: Talk
Title: Searching for FRBs with ALERT
Abstract:
The APERture Tile In Focus (Apertif) receiver system will serve as an important test-bed for the SKA by effecting a factor-of-30 increase in field of view on the Westerbork Synthesis Radio Telescope (WSRT). With ALERT, we will take advantage of Apertif’s 9,deg$^2$ sky coverage to search for fast radio bursts (FRBs) at a forecasted rate of several detections per week. We will also have the ability to trigger LOFAR, where FRBs will arrive roughly a minute later, and where they can be localized to arcsecond precision. In this talk I will describe the commissioning of Apertif, and give updates on our first pulsar observations, as well as on-sky tests of our real-time FRB detection pipeline. I will also discuss the ALERT science case, and our summer plans of running an incoherent transient search over the full FoV. |
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Name: Connors, Riley
Talk/Poster: Talk
Title: Disentangling the physical mechanisms at play in sub-Eddington black hole accretion
Abstract:
X-ray spectral modelling of accreting black holes - both X-ray binaries observed in the hard state, and low-luminosity active galactic nuclei - shows that non-thermal power-law emission typically dominates. There are several processes/geometries capable of producing this emission: inverse Compton scattering of disc photons by coronal (spherical or co-planar with the disc) electrons, synchrotron self-Compton scattering of synchrotron photons by hot electrons in the jet, or non-thermal synchrotron emission from accelerated particles (in the jet or in the inner accretion flow/corona). In order to discern the contributions of these emission processes and understand the geometry of the inflow/outflow, one needs to model broadband emission including components further out in the jet (such as the self-absorbed synchrotron emission which produces flat-spectrum jet emission). I will show that including variability information within this broadband modelling approach allows further breaking of degeneracies.
I show the joint modelling of multiple observations of a few sources, including the Galactic centre black hole, Sgr A*, the most quiescent confirmed black hole candidate X-ray binary, A0620-00, and a well-studied X-ray binary in its hard state, GX 339-4. Further work focuses on better understanding the relationship between the X-ray irradiating source and reflection of those X-rays off the accretion disc. |
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Name: Contreras, Yanett
Talk/Poster: Poster
Title: Initial gas structure in cold, massive clumps: Cluster formation in its earliest stages
Abstract:
The two main models for high-mass star formation, ‘core accretion' and ‘competitive accretion,' predict different internal structures for cluster forming clumps only in the very earliest stages. The best way to distinguish between these models therefore is to identify cold, cluster-forming clumps and measure their internal structure directly.
Observations of Galactic plane surveys have allowed us to determine the physical global properties of proto-cluster candidates in the Galaxy. Using data from ATLASGAL and Hi-Gal dust continuum surveys and the MALT90 molecular line survey, we have compiled information about the mass, density, luminosity and temperature of more than 1000 clumps in the Galaxy, identifying several clumps that satisfy all the requirements for cluster-forming clumps in very early stages of evolution and making possible the selection of the best candidates of clumps in the verge of star formation, for follow up observation of their small-scale structure with ALMA.
Here we present the properties derived for star forming clumps in the Galaxy and our ALMA observations of the continuum, and molecular line toward some of these clumps, which have allow us to measure its internal structure and assess whether the cores are gravitationally bound and collapsing. |
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Name: Dabhade, Pratik
Talk/Poster: Talk
Title: LoTSS of GRGs
Abstract:
Giant Radio Galaxies (GRGs) are the single largest objects known in the Universe. Their sizes extend from 0.5 Mpc to ~5 Mpc. The ‘central engine’ is an accreting SMBH of mass 10^8 to 10^10 msun which is responsible for the ejection of the collimated, bipolar relativistic jets orthogonal to an accretion disc. GRGs are believed to be the last stop of radio galaxy evolution owing to their sizes. This helps in imposing constraints on evolutionary models of radio galaxies. GRGs can serve as outstanding probes of the IGM. GRGs can also transport enriched material from the host galaxy to large distances and pollute the IGM with non-thermal particles and magnetic fields. Low frequency surveys are ideal to search for new GRGs as the radio emission is least suppressed by spectral ageing effects in the extended radio lobes and is prone to detect more diffuse relic plasma from lobes of GRGs. We use the new LOFAR Two-metre Sky Survey (LoTSS) which is a deep 120-168 MHz imaging survey and its early data release provides images with unprecedented sensitivity (0.5 mJy) and resolution (25”). This makes it ideal for GRG (re)search. We have found ~ 300 GRGs from the LoTSS, of which several are hosted by quasars with z >1. Work is currently ongoing to make a complete sample of GRGs for further studies. I shall be presenting methods employed in this work, above mentioned results in detail and the future multiwavelength work. |
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Name: Davelaar, Jordy
Talk/Poster: Poster
Title: The effects of accelerated particles on the radiative properties of accreting black holes
Abstract:
When modeling emission of accreting black holes, one often assumes that the source of the radiation is a thermal electron population. However, the observations of the SED of M87 show a power law that hints to the presence of accelerated particles. These particles are expected to get accelerated in high magnetized regions inside the jet and/or disk. The electron distribution function is typically not simulated in GRMHD simulations, so a parameterization is needed. To this end, we use the kappa distribution function, which smoothly connects a thermal core with a high energy power law, which can be characterized by one free parameter; kappa. We insert accelerated particles inside the jet only. In this presentation, I will show our latest result from these GRMHD simulation combined with our post-processed radiative transport code RAPTOR, and show how the source sizes and SEDs of accreting black hole models of M87 and Sgr A* are affected if we assume that emission is produced by both thermal and accelerated particles. Understanding the effect of accelerated particles on the observational parameters such as source size, is crucial for the interpretation of the upcoming science observations of the Event Horizon Telescope. |
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Name: Dayal, Pratika
Talk/Poster: Talk
Title: The first billion years of galaxy formation in cold and warm dark matter cosmologies
Abstract:
Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: as the first sources of light, these galaxies ended the 'cosmic dark ages' and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the shapeless ellipticals galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. At the forefront of astronomical research, the past few years have seen cutting-edge instruments provide tantalising glimpses of such galaxies chaotically assembling in an infant Universe. I will show how this data has provided an unprecedented opportunity to pin down the reionization state of the Universe (at least in its last stages), understand their physical properties, and study the key physics driving their formation and evolution. Finally, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope and the associated reionization history, can provide a powerful testbed for Warm Dark Matter models. |
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Name: de Boer, Jos
Talk/Poster: Poster
Title: Protoplanetary disk geometry derived from VLT/SPHERE images of the scattering surface
Abstract:
Planet or brown dwarf companions orbiting in or near protoplanetary disks will alter the shape of their native disks. The scattering surfaces of protoplanetary disks often contain a wealth of structure, such as gaps, rings and spiral arms when we observe them at high angular resolution.
To determine whether these disk structures are caused by interaction with a nearby companion requires detailed analysis of the geometry of these systems. High-contrast imaging with VLT/SPHERE has allowed us to determine the height of the scattering surfaces in disks with multiple rings and to place constraints on the effects of planet-disk interactions. Additionally, the height information allows us to apply a height-corrected deprojection (or rotation) of the disk image, which mimics the phase-on appearance of an inclined flaring disk. The height information will become a crucial parameter to compare the distribution of small grains at the scattering surface with ALMA images of (sub)mm-sized dust located at the disk mid-plane. We will present these methods for SPHERE images of the disks around RX J1615 and HD 34282. |
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Name: de Vries, Martijn
Talk/Poster: Talk
Title: Thermal and Non-thermal X-ray Emission in the Environment of the Powerful Radio Galaxy Cygnus A
Abstract:
We present results from the Cygnus A XVP project based on the first 1 Msec of a total of 2 Msec Chandra ACIS exposure.
Within its cocoon shock, Cyg A shows extended X-ray jets that do not spatially coincide with the observed radio jets. This implies that the X-ray jets are Inverse Compton emitting relics, left over by earlier passage of the radio jet. We aim to shed more light on the nature of these jets and their surrounding lobes by characterizing the non-thermal emission that they emit. We have created two different models to describe the jet, lobe and ICM emission: one model including only thermal emission, and one model including a mixture of thermal and non-thermal emission.
However, standard fitting routines do a poor job of separating the bright, hot intracluster medium from a power-law spectrum. With the help of MCMC sampling and certain model selection tests, we compare the two models and find that our model selection favours the model in which non-thermal emission is included. The MCMC sampling also allows us to characterize the non-thermal emission of this model in detail. We find that, assuming the non-thermal emission in both the jets and lobes is IC emission, the jets would be overpressured by a factor of a few with respect to the surrounding lobes, which would lead them to expand and fade out on very short timescales.This would imply that the jets emit synchrotron rather than IC emission. |
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Name: Decleir, Marjorie
Talk/Poster: Talk
Title: The variation of the dust attenuation curve in the nearby Universe.
Abstract:
Dust attenuation is a crucial but highly uncertain parameter that hampers the determination of intrinsic properties of galaxies, such as stellar masses, star formation rates and star formation histories. In extragalactic studies, the dust attenuation law is usually assumed to be similar as in the Milky Way, but there is growing evidence for strong deviations from a universal dust attenuation law.
To investigate the variations in the shape of the dust attenuation curves and the dust properties in nearby galaxies of the KINGFISH sample, we have initiated the project DustKING. By fitting theoretical models with varying dust extinction properties to a set of multi-wavelength data, it is possible to constrain the spectral energy distributions (SEDs) and the dust attenuation curves of nearby galaxies. Particularly important for our goal are UV data from the SWIFT telescope: the three UVOT filters uniquely cover the dust absorption feature at 2175 Å, which enables us to characterise the slope and bump strength.
We present the first results of our analysis for the spiral galaxy NGC628. We find that the observed UV colours appear most consistent with a Milky Way extinction curve and that they do not at all agree with the Small Magellanic Cloud curve. At first sight, the UV slope of the attenuation curve of NGC628 is thus rather shallow and the dust properties seem to be consistent with those in the Milky Way. Furthermore, we fitted realistic galaxy SED models to the data and compared the obtained results with the colour analysis. |
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Name: Domcek, Vladimir
Talk/Poster: Poster
Title: X-ray synchrotron filaments in Cas A: the radio connection
Abstract:
One of the most important themes in X-ray research of the supernova remnants (SNRs) over the last 10-20 years has been cosmic-ray acceleration by SNR shocks. The detection of the X-ray synchrotron emission has proven that young SNRs can accelerate electrons to energies up to 10-100 TeV, which requires a high level of magnetic field turbulence. The narrow widths of the X-ray synchrotron filaments in some young SNRs has also shown that magnetic fields are amplified too.
A prediction of an efficient acceleration is that the electron cosmic-ray spectra should not be a power-law but instead should flatten toward the higher energies. Here we test this hypothesis by investigating the spectral index of thin X-ray filaments in Cas A, by comparing the X-ray and the radio fluxes. By doing this we avoid having to model the effects of synchrotron cooling as much as possible, and hence, a "one zone model" is sufficient. So far we found a need for spectral curvature. We discuss the implications for this in the context of non-linear shock acceleration and the effects of magnetic field turbulence. |
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Name: Driessen, Laura
Talk/Poster: Talk
Title: LOFAR studies of G54.1+0.3 - a close cousin of the Crab
Abstract:
The Crab is a quirky supernova remnant, which lacks a large-scale thermal shell and is surrounded by a shell of cold ejecta dust. In fact, the Crab Nebula isn’t really a supernova remnant at all; it is a pulsar wind nebula powered by ongoing energy output from the central Crab Pulsar. Until recently, the Crab was considered largely unique in its features. G54.1+0.3 is a supernova remnant with a pulsar and pulsar wind nebula. Like the Crab, it also lacks evidence of a large scale thermal shell. Because of these characteristics and the similar morphology of the pulsar wind nebula it has long been considered a close-cousin of the Crab. Earlier this year it was confirmed that G54.1+0.3 is surrounded by a shell of cold ejecta dust, making it a closer-cousin than previously thought. Investigating these objects could tell us a lot about the physics of supernovae, the formation of dust in our Galaxy and in high-redshift galaxies, the formation of particles in neutron star magnetospheres, the evolution of pulsar wind nebulae and more. I will present a multi-frequency investigation of G54.1+0.3 - including LOFAR high-band imaging - and a comparison between G54.1+0.3 and it’s cousin, the Crab. |
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Name: Edstam, Louise
Talk/Poster: Poster
Title: Binary black hole formation through chemically homogeneous evolution
Abstract:
The recent detection of binary black holes has caused many researchers to question how they are formed. Currently there are two main directions of competing theories: (1) dynamical formation and (2) evolutionary formation. Here we take a closer look at chemically homogeneous evolution which is one of the evolutionary formation channels.
It has been shown that the first gravitational wave event, GW150914, can be explained by chemically homogeneous evolution. I am investigating whether the second gravitational wave event, GW151226, could be explained by this type of evolution The goal is to be able to make predictions, for example of surface abundances, that can be observationally tested to confirm or reject the chemically homogeneous evolutionary channel. |
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Name: Elenbaas, Chris
Talk/Poster: Talk
Title: Magnetar giant flare high-energy emission
Abstract:
High energy (> 250 keV) emission has been detected persisting for several tens of seconds after the initial spike of magnetar giant flares. It has been conjectured that this emission might arise via inverse Compton scattering in a highly extended corona generated by super-Eddington outflows high up in the magnetosphere. In this paper we undertake a detailed examination of this model. We investigate the properties of the required scatterers, and whether the mechanism is consistent with the degree of pulsed emission observed in the tail of the giant flare. We conclude that the mechanism is consistent with current data, although the origin of the scattering population remains an open question. We propose an alternative picture in which the emission is closer to that star and is dominated by synchrotron radiation. The RHESSI observations of the December 2004 flare modestly favour this latter picture. We assess the prospects for the Fermi Gamma-Ray Space Telescope to detect and characterise a similar high energy component in a future giant flare. Such a detection should help to resolve some of the outstanding issues. |
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Name: Ellerbroek, Lucas
Talk/Poster: Poster
Title: The footprint of cometary dust in the lab
Abstract:
Comets are thought to be the most pristine bodies in the solar system that have survived to this day. In-situ measurements of cometary dust therefore provide a unique window on dust growth mechanisms during the onset of planet formation. Measurements by the Rosetta spacecraft have shown that the dust lifted off the surface of the comet 67P/Churyumov-Gerasimenko has a granular and in some cases fractal-like structure up to sub-micron sizes. This indicates that hierarchical growth may be universal across size scales. However, the dust particles may be affected by their entry in the spacecraft, changing their shape and, possibly, structure. I will present the results of a series of laboratory experiments that simulate the impact of dust on the Rosetta detector surfaces, and some of our remarkable findings and their implications for the question whether comets really are as pristine as we think. |
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Name: Escorza, Ana
Talk/Poster: Talk
Title: To Ba or not to Ba: observational constraints to the formation and evolution of Barium stars
Abstract:
Our project focuses on the poorly understood formation channels of a family of chemically peculiar stars known as barium (Ba) stars. These are main-sequence or giant stars which show excess of products of the slow-neutron-capture process of nucleosynthesis. These overabundances cannot be explained by single star evolution theory because the s-process only takes place at the end of the AGB phase. Ba stars are known to be formed in binary systems where a former AGB companion (now a dim white dwarf) polluted the current Ba star with enriched products. A long-standing problem is, however, that their observed properties are not predicted by models, indicating that binary interaction processes are not well understood.
In this contribution, we will show the first HR diagram of Ba stars using GAIA parallaxes. New results of our long-term radial velocity monitoring will also be presented in the form of well determined orbital elements. By analysing their mass and period distributions, we want to investigate the evolutionary link between main sequence and giant Ba stars. Comparing these observations with our state-of-the-art evolutionary models, our ultimate goal is to come to a prescription of the initial conditions and interaction processes required for a binary system to evolve into a Ba star. |
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Name: Farnes, Jamie
Talk/Poster: Poster
Title: Observed Faraday Effects in Damped Lyman-Alpha Absorbers and Lyman-Limit Systems
Abstract:
Protogalactic environments are typically identified using quasar absorption lines, and these galactic building blocks can manifest as Damped Lyman-Alpha Absorbers (DLAs) and Lyman Limit Systems (LLSs). We use radio observations of Faraday effects to test whether DLAs and LLSs host a magnetised medium, by combining DLA and LLS detections throughout the literature with 1.4 GHz polarization data from the NRAO VLA Sky Survey (NVSS). Using a Bayesian framework, we are unable to detect either coherent or random magnetic fields in DLAs. However, we find strong evidence that LLSs host random magnetic fields, with a 95.5% probability that LLS lines-of-sight have lower polarized fractions than a control sample. The regular coherent magnetic fields within the LLSs must be ≤ 2.4 μG, and the magnetised gas must be highly turbulent with a typical scale on the order of ≈ 5–20 pc, which is similar to that of the Milky Way. This is consistent with the standard dynamo pedagogy, whereby magnetic fields in protogalaxies increase in coherence and strength as a function of cosmic time. Our results are consistent with a hierarchical galaxy formation scenario, with the DLAs, LLSs, and strong magnesium II (Mg ii) systems exploring three different stages of magnetic field evolution in galaxies. |
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Name: Frantseva, Kateryna
Talk/Poster: Talk
Title: Delivery of organics to Mars through asteroid and comet impacts
Abstract:
The recent discovery of methane in the Mars atmosphere and organic molecules in drill samples taken by Curiosity is surprising, as photodissociation and photodegradation would destroy most organics within hours. While burying in the subsurface will increase the lifetime, it is clear that organics must have been delivered in geologically recent times, presumably by impacts of asteroids, comets, and/or interplanetary dust particles (IDPs).
The IDP-borne organic flux on Mars was estimated to be 1.2 times 10^6 kg/yr by Flynn (1996). We calculate for the first time the flux from asteroids and comets.
We have performed numerical gravity simulations of impact rates on Mars within the past few Myr. We use the N-body integrator RMVS/Swifter to propagate the Sun and the eight planets from their current positions. Separately, we add comets and asteroids to the simulations as massless test particles, based on their current orbital distributions. In our asteroid simulations we focus on organic-rich (C-class), basing ourselves on the dynamical model by Greenstreet et al. (2012) and on the measured distribution of taxonomic types across the Main Asteroid Belt. For the comets we assume a constant organic fraction.
Preliminary results show that the organic flux is sim 10^6 kg/yr for asteroids, comparable to the IPD rate; asteroids certainly cannot be neglected. Comets, on the other hand, contribute only sim 0.0002 times 10^6 kg/yr and can be neglected in the process of organic delivery to Mars. |
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Name: Gardenier, David
Talk/Poster: Poster
Title: FRBPOPPY - Fast Radio Burst Population Synthesis in Python
Abstract:
Despite first being detected a decade ago, fast radio bursts (FRBs) still elude our understanding in terms of origin and underlying population. Establishing the origin of FRBs is a key goal in radio astronomy, with significant investments being made into the development of both instrumentation and software capable of solving that question. A whole range of fast transient surveys will be coming online in the near future, and will be a treasure trove for studies of the cosmological population of FRBs. In preparation for new FRB surveys I have developed frbpoppy, an FRB population synthesis code. It will provide not just fast transient detection rates, but it will also further our understanding of FRB emission properties. Frbpoppy has been designed to combine cutting-edge results with ease of use, from automated syncing with the latest frbcat to modular code and interactive plotting. With recent observations ruling out a cataclysmic-event origin for at least some FRBs, the time has come to capitalize on available theories and help uncover the nature of the mysterious FRBs via population synthesis! |
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Name: Georgiou, Christos
Talk/Poster: Talk
Title: Shapes of galaxies in multiple broad-band filters
Abstract:
Weak lensing is a powerful tool for studying cosmology and gravity. However, the weak lensing signal is contaminated by the intrinsic alignment signal, which is caused by the alignment of galaxies with the tidal gravitational field at the time of structure formation. Understanding and modelling this signal is essential for high precision weak lensing measurements. In this talk I will look into the difference of galaxy shapes measured in different broad band filters and the dependence of the intrinsic alignment signal. I will showcase DEIMOS, a sophisticated moment-based shape measurement method, applied on galaxies from the spectroscopic Galaxy And Mass Assembly survey combined with deep imaging data from the Kilo Degree survey. |
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Name: Gotberg, Ylva
Talk/Poster: Poster
Title: The ionizing contribution from stripped stars on stellar populations throughout cosmic time
Abstract:
Massive stars are observed to be most commonly in binaries. Despite this fact are massive stars usually considered as single stars in population models. The evolution of a star in a binary can differ significantly from the evolution of a single star. Binaries can strip off envelopes, spin up and even merge. All of these evolutionary paths may give rise to increased ionising flux.
We model stars that have been stripped of their hydrogen-rich envelopes through Roche-lobe overflow. We use the stellar evolution code MESA to model the evolution and structure of the stripped stars. To accurately investigate the appearance of the stripped stars we tailor-make atmospheres using the non-LTE radiative transfer code CMFGEN.
Our models reveal un-accounted flux of hydrogen and helium ionising radiation. The amount of emitted ionising photons shows dependencies on metallicity and wind mass loss rates. |
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Name: Gourdji, Kelly
Talk/Poster: Poster
Title: Searching for repeat Fast Radio Bursts using the Arecibo telescope
Abstract:
Fast Radio Bursts (FRBs) are bright, millisecond-long radio pulses of extragalactic origin. The search for FRBs and what creates them have garnered much interest within the astronomical community, as well as the general public. The discovery of repeat bursts from FRB121102, the only known repeater, has bolstered the search for viable progenitor models, as they can no longer be cataclysmic in nature. Studying the pulse morphology can help with this endeavor. To do so, we have observed FRB121102 using the Arecibo telescope and developed a pipeline to search for additional bursts. This poster describes the pipeline and preliminary results on the additional bursts found thus far. In particular, we present the most interesting types of bursts from our sample, and some statistics on the burst characteristics of our sample. We also show how this pipeline is being applied to search for repeat bursts from FRB130628. This FRB was discovered with the Parkes telescope, which is 10 times less sensitive than the Arecibo telescope. It is possible that Parkes is only picking up the strongest bursts and that Arecibo will allow us to detect fainter repeat bursts. To test this hypothesis, we have taken observations of this sky position using Arecibo and are running these data through the pipeline developed for the repeating FRB. |
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Name: Greenwood, Aaron
Talk/Poster: Talk
Title: Brown dwarf protoplanetary discs: disc chemistry and prospects of planet formation
Abstract:
We use ALMA observations of the brown dwarf disc Rho Oph 102 create a small grid of thermochemical models of a "typical" brown dwarf protoplanetary disc. I will discuss the evidence which supports the idea that M dwarf discs are similar to T Tauri discs, but simply scaled down in mass and radius. Finally, I will review the possibilities for planet formation in discs where the star straddles the stellar / substellar boundary. |
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Name: Gusinskaia, Nina
Talk/Poster: Talk
Title: Conquering systematics for a precision pulsar test of Einstein's equivalence principle.
Abstract:
PSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system containing two white dwarfs. The pulsar orbits the inner white dwarf every 1.6 days. In turn, this inner binary system orbits the outer white dwarf every 327 days. The gravitational influence of the outer white dwarf strongly accelerates the inner binary, making this system an excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity - especially because the neutron star has significant gravitational self-binding energy. This system has been intensely monitored using three radio telescopes: Arecibo, Green Bank and Westerbork. Using the more than 30000 pulse times of arrival (TOAs), we have modeled the system using direct 3-body numerical integration and performed an initial SEP violation test. I will present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which can limit the precision to which we can test the SEP in this system. For example, we are applying Fourier-based techniques to the residuals in order to isolate the effects of systematics that could masquerade as an SEP violation. We are also evaluating how different aspects of the TOA production process affect the inferred systematics. Our ultimate goal is to provide an SEP test that is robust to the complications in modeling the astrophysics of the system, and which maximizes the precision we can achieve. |
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Name: Guzman-Ramirez, Lizette
Talk/Poster: Poster
Title: Opening PANDORA's box: an APEX survey of CO in planetary nebulae
Abstract:
Millimetre carbon monoxide (CO) emission is the most useful probe of the warm molecular component ejected by low to intermediate mass stars during the asymptotic giant branch (AGB) phase. CO is the second-most abundant molecule in the Universe and the millimetre transitions are easily excited, thus making it particularly useful to study the mass, structure, and kinematics of the molecular gas. We present a large survey of the of CO (J = 3-2) line taken using the Atacama Pathfinder EXperiment (APEX) telescope in a sample of 93 planetary nebulae. This survey was designed to study the circumstellar shells of evolved stars, to investigate the frequency of occurrence of the multiple wind phenomenon and how it is related to the stellar chemistry, mass-loss rate, and evolutionary stage. CO (J = 3-2) was detected in 35 of the 93 objects observed. |
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Name: Hartsuijker, Ard
Talk/Poster: Talk
Title: The Dwingeloo Radio Telescope for Education and Public Outreach
Abstract:
Since 2007 the CAMRAS volunteers maintain and use ASTRON’s Dwingeloo Radio Telescope for amateur astronomy, ham radio experiments, education and for public events such as Heritage Day (Open Monumentendag) and Science Weekend (Weekend van de Wetenschap).
Youth visit the telescope for demonstration or observations. School kids experience the “live” beat of a pulsar on its way to the earth for more than a thousand years. High school students observe a pulsar and calculate its period and its distance with the aid of the dispersion measure. Or they observe neutral hydrogen in the Galaxy (or neighbouring galaxies) and map the distribution.
With homemade YAGI antennas we involve scouts in ham radio experiments. With their antennas and help of radio amateurs they contact each other with radio messages over the moon via the Dwingeloo telescope.
During tours and public events the emphasis is on the history of the oldest rotating radio telescope in the world and to listen to a live demonstration of signals from radio sources in the universe.
For artists the radio telescope provides unknown possibilities for audio and visual arts. They use the weak radio waves from the universe, or the waves reflected by the moon, new art forms. With their art artists bring science and technology to another, an artistic way to the attention of the audience, the listener or viewer.
Ard Hartsuijker and Marc Wolf (CAMRAS) |
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Name: Hörandel, Jörg
Talk/Poster: Talk
Title: Tracing the highest-energy particles in the Universe: Radio detection of cosmic rays
Abstract:
The origin of the highest-energy particles in the Universe is one of the key open questions in astroparticle physics. High-energy cosmic rays impinging onto the atmosphere of the Earth initiate extensive air showers. Recently, we have established a new technique to detect cosmic rays: the measurement of radio emission from extensive air showers. We measure the properties of cosmic rays - their arrival direction, their energy, and their type of particle/atomic mass with the LOFAR radio telescope and with the Pierre Auger Observatory in Argentina. We will review recent results, illustrating the breakthrough of the radio detection and illustrate the impact on cosmic-ray measurements. We will also discuss future projects, such as the 3000 km2 radio detector at the Pierre Auger Observatory in Argentina which will open a new window to the high-energy Universe. The results from this new array will be curtail to understand the origin of the highest-energy cosmic rays. |
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Name: Heikamp, Stephanie
Talk/Poster: Talk
Title: Deconvolution of polarimetric datasets of simulated and observed circumstellar disks
Abstract:
Polarimetric images of circumstellar environments, even when corrected with adaptive optics, have a limited angular resolution. The finite resolution greatly affects polarimetric images due to the cancelling of adjacent polarization signals with opposite signs. When commonly-used deconvolution methods are applied to polarized intensity images, significant artifacts can be created and real polarization signals are ignored.
We explore the effects of a finite point-spread function (PSF) on polarimetric images and the application of Richardson-Lucy deconvolution to polarimetric images. We use this knowledge to develop an algorithm that can deconvolve Stokes Q and U images. Our algorithm is based on Maximum Entropy with priors suitable for circumstellar polarimetric imaging and iterative update equations that enforce azimuthal symmetry and allow for positive and negative values in the data. We apply our novel deconvolution technique to simulated circumstellar disk models and observed polarimetric data of BP Piscium.
The most significant effect of finite angular resolution is the loss of polarimetric signal close to the central star where large polarization signals of opposite sign average out. It remains difficult to retrieve central signal smaller than the FWHM of the PSF. Deconvolution of intensity images or polarized intensity images can lead to reducing the signal into a smaller area corresponding to the FWHM of the PSF whereas our deconvolution method retrieves the shape and structure of the original simulated circumstellar disk model. |
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Name: Hesp, Casper
Talk/Poster: Talk
Title: Three-dimensional Simulations of Tilted Black Hole Accretion: Jets, Alignment and Precession
Abstract:
Black hole (BH) accretion naturally produces relativistic jets that transport energy from BHs to distances over millions times larger. Importantly, most accretion flows are tilted with respect to their BH, because the gas infalling from large distances is unaware of the direction of the BH spin. Despite the misalignment being an extremely common feature of BH accretion, it remains poorly explored. Are tilted disks capable of producing jets? If so, how stable are these jets? Do they follow the BH spin axis or the rotation axis of the infalling gas? Such questions remain unanswered because the tilt adds to the long list of formidable challenges such as (i) General-Relativistic (GR) effects, (ii) magnetized disk turbulence, which calls for a high-resolution 3D Magnetohydrodynamic (MHD) treatment, (iii) jet regions are dominated by magnetic energy, making evolution of the system extremely sensitive to numerical errors, and (iv) prohibitive scale separation of 106 between the BH and galaxy scales. Using our self-developed GPU-based GRMHD code H-AMR we simulated tilted accretion disk-jet systems of black holes at the highest resolution ever reported, opening up a completely new regime for computational studies of BH accretion and jet formation. We find that jets tend to align with the rotation axis of accreted material instead of with the BH. Over time, disk-jet systems show precession and partial alignment with respect to the black hole spin. These findings can help to constrain possible explanations for quasiperiodic signals (QPOs) in BH accretion systems. |
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Name: Hessels, Jason
Talk/Poster: Poster
Title: Fast Radio Bursts: A look back at the first decade of a new transient phenomenon
Abstract:
In 2007, astronomers using the Parkes radio telescope identified the first example of a new type of transient astrophysical phenomenon: the 'Fast Radio Burst' (FRB). Lasting for only a few milliseconds, the FRBs also show a large dispersive sweep that suggests they originate from cosmological distances. If so, the implied energetics are extreme. Many theories for the physical nature of the FRBs have been proposed - including both cataclysmic events involving neutron star collision (or collapse), along with non-cataclysmic scenarios involving a young and/or highly magnetized neutron star. While some FRBs appear to be one-off events - supporting a cataclysmic origin - a sporadically repeating FRB has also recently been discovered and localized to a dwarf galaxy at redshift z = 0.19. It is thus currently unclear whether there is a single type of FRB, or whether we are seeing multiple source populations. Looking back at the past decade of discoveries, I will review our current observational and theoretical understanding of the FRBs. With the first precision localization now in hand, and with an international suite of FRB telescopes under construction, I will also give a look forward to what the next decade of FRB science may hold: perhaps a definitive solution to the puzzle of their origin, and the first serious steps towards using FRBs as probes of the intergalactic medium. |
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Name: Hodge, Jacqueline
Talk/Poster: Talk
Title: ALMA observations of resolved, high-z dusty star formation
Abstract:
Understanding how galaxies formed their stars over cosmic time is one of the most fundamental questions in astronomy. Yet until recently, our knowledge of high-redshift star formation was largely limited to the unobscured stellar populations observable in the (rest-frame) optical/UV, with details of the star-forming interstellar medium either missing entirely or limited to unresolved observations. I will present new ALMA results that allow us to resolve the obscured star formation and cold molecular gas in z=2 submillimeter galaxies on kpc-scales. The observations provide evidence for compact (R_e ~ 1.8+/-0.2kpc) dusty cores, with light profiles consistent with smooth exponential disks (Sersic index of n=0.9+/0.2). We compare our results to comparable–resolution HST H160-band images, finding that the stellar morphologies appear significantly more extended and disturbed, and suggesting that commonly used SED fitting routines may be too simplistic. Finally, we present new evidence that the dust emission is significantly more compact than the cold gas reservoirs, and we discuss the implications of our results for common methods to trace the high-z ISM, as well as in general for early massive galaxy formation. |
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Name: Igoshev, Andrei
Talk/Poster: Talk
Title: The velocity anisotropy in an ensemble of millisecond radio pulsars
Abstract:
The millisecond radio pulsars (MSPs) are considered to be promising tools to detect the gravitational wave background. That is why recently the precise measurements were performed for distances and proper motions of multiple MSPs. According to the binary stellar evolution, the MSP can be only formed in binaries which stay bound after the primary supernova explosion and go through the second mass transfer to spin-up the old NS. Such a binary receives a composite kick consisting of the part caused by the instantaneous mass loss and the NS natal kick.
The ensemble of MSPs is in dynamical equilibrium in the Galactic gravitational potential. I use the modified Schwarzschild method to estimate the distribution function. The instantaneous velocity distribution of the local MSP ensemble is strongly anisotropic because the Galactic gravitational potential has a pronounced disk component. Namely, the expected vertical velocity dispersion appears to be two times smaller than the radial velocity dispersion. Moreover, the present velocity distribution is non-linearly related to the initial distribution of systemic velocities. |
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Name: Issaoun, Sara
Talk/Poster: Poster
Title: High-resolution imaging of the 3mm SiO maser emission in the disk-wind from a massive protostar
Abstract:
Massive stars are crucial to the evolution of galaxies: they are the main source of heavy elements and UV radiation and they provide turbulence to the interstellar medium, greatly affecting star and planet formation processes. However, high-mass star formation still remains an unexplained phenomenon due observational difficulties, such as high dust extinction and large distances, which hinder attempts to resolve disk-accretion and outflow-launching regions of protostars. With very long baseline interferometry (VLBI), maser radiation from different molecules in shock regions between outflows and the interstellar medium close to high-mass protostars can be detected and imaged. These masers are ideal probes of early-stage high-mass star formation: they arise in bright compact spots and can be tracked with VLBI to study gas kinematics at the highest angular resolution. Source I, in Orion, is the closest known massive young stellar object (YSO) and exceptionally powers SiO masers at radii within 100 AU, providing a unique chance to study its innermost dynamics. These masers have been previously imaged with VLBI at 43 GHz (7mm), and detected with a single baseline at 86 GHz (3mm). I will present the first VLBI images of the 28SiO v=1, J=2-1 maser emission around Source I observed at 86 GHz and compare them with previous images of the 7mm masers, which together enable a better understanding and overview of the physical conditions favorable to these maser transitions in the context of dynamical processes around a massive YSO. |
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Name: Janssen, Michael
Talk/Poster: Talk
Title: A data reduction pipeline for the Event Horizon Telescope
Abstract:
The Event Horizon Telescope (EHT) is an international consortium with the aim to make the first image of a black hole's shadow. In April 2017 ALMA, APEX, SPT, IRAM 30m, LMT, SMT, JCMT and the SMA joined together to observe the central nucleii of Sgr A*, M87 and a few other AGN sources. With a resolution of 23 microarcseconds and a bandwidth of 4GHz, it will be possible to identify the expected distinctive shadow feature in the radio interferometric images of Sgr A* and M87.
Developers at JIVE are working together with the Black Hole Cam team at Radboud University Nijmegen to build a pipeline for a streamlined reduction of Very Long Baseline Interferometry(VLBI) data in the millimeter(mm) regime, which will be extremely valuable for the EHT. The basis for this will be the CASA software package, to which we are adding crucial new capabilities for the handling of VLBI data. CASA can then be used for the processing and imaging of the whole spectrum of radio data: single-dish, connected interferometers and VLBI.
In my presentation I will talk about the EHT run in April and our mm VLBI data processing pipeline, focusing on its role within the general EHT data analysis machinery. |
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Name: Johnston, Cole
Talk/Poster: Poster
Title: Asteroseismology of close binary pulsators
Abstract:
Stellar evolution is driven by the physical processes occurring deep in the stellar interior, by the dynamics in the outer stellar envelope, and in the case when a star is in a binary or multiple system, by the tidal interactions between the components. While these physical processes are understood in a general sense, theoretical calculations involving them are largely unconstrained in modern stellar evolution codes. Particularly in massive stars, which drive the dynamical and chemical evolution of galaxies and the interstellar environment, theoretical evolution codes cannot match observationally determined stellar parameters and use artificially adjusted physical parameters such as convective core overshooting and/or chemical mixing. Here we discuss the synergistic use of asteroseismology with binary modeling as a necessary observational constraint to cross calibrate the internal physics that govern stellar evolution such as rotational mixing, overshooting, and angular momentum transport. We provide several examples of suitable binaries to perform calibrations for stellar modeling, covering a wide range in masses and evolutionary states. |
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Name: Kamp, Inga
Talk/Poster: Poster
Title: Origin of ices in T Tauri disks and observing prospects
Abstract:
We use Monte Carlo continuum radiative transfer models of a representative T Tauri disk to derive for the first time self-consistently the location of water ice and subsequently the thermal emission features at 40 and 60 micron. We provide results on the robustness of these features against disk mass, disk sizes and varying dust properties. We demonstrate that future observations (e.g. SOFIA/HIRMES, SPICA/SAFARI) will be able to distinguish between ices inherited from an earlier molecular cloud phase versus in-situ formed or processed ices. This is highly relevant for linking disks to observations of comets in our own Solar System such as the Rosetta results on 67P/Churyumov-Gerasimenk.We use Monte Carlo continuum radiative transfer models of a representative T Tauri disk to derive for the first time self-consistently the location of water ice and subsequently the thermal emission features at 40 and 60 micron. We provide results on the robustness of these features against disk mass, disk sizes and varying dust properties. We demonstrate that future observations (e.g. SOFIA/HIRMES, SPICA/SAFARI) will be able to distinguish between ices inherited from an earlier molecular cloud phase versus in-situ formed or processed ices. This is highly relevant for linking disks to observations of comets in our own Solar System such as the Rosetta results on 67P/Churyumov-Gerasimenk. |
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Name: Keller, Denise
Talk/Poster: Talk
Title: The VLA view on the clumpy molecular shells of CW Leo
Abstract:
The carbon-rich AGB star CW Leo has a high mass-loss rate, is nearby (~130 pc), and is one of the most important chemical laboratories in astronomy. The star has been proposed to have a binary companion which largely impacts the hydrodynamical shaping and chemistry of the circumstellar envelope (CSE). The combined effects of dynamics and chemistry are not well understood. We have obtained a new spectral and imaging survey of CW Leo at cm-wavelengths using the Jansky Very Large Array (VLA). The molecular distribution in the outer CSE is traced in unprecedented detail with a sensitivity of ~1 mJy and a resolution of ~1 arcsec. Numerous molecular line transitions are detected which probe the region of UV-photon induced chemistry. Our spatio-kinematical analysis provides a detailed empirical description of this narrow density-enhanced region which consists of shells, arcs, and clumps and clearly shows asymmetries. Our analysis emphasises that the complex morphology greatly affects the photochemical properties of the CSE. This has to be taken into account in future studies to approach a global understanding of the CSE of CW Leo and of AGB stars in general. |
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Name: Klarmann, Lucia
Talk/Poster: Poster
Title: Constraining protoplanetary disk composition with Interferometry
Abstract:
Terrestrial planets and super-earths form in the inner regions of protoplanetary disks. The dust in this region is not only the base material for planet formation, but the refractory properties of its different components also define the shape of the inner disk and the position of the inner rim.
Using NIR interferometry, it is possible to obtain values for position of the inner rim. But these values depend on assumptions about the inner rim geometry.
We use radiative transfer (RT) modeling to compare values from interferometric observations with physical disk properties. We calculate NIR visibilities from a wide range of RT disk models with different dust compositions and grain size distributions. From these visibilities we calculate values for the inner rim position, assuming different inner disk geometries.
We find that there is a difference between the position of the physical disk rim from the RT model and the values obtained by the visibility modeling. The geometry that is used for t visibility modeling is important. Smooth flux distributions like a half Gaussian ring lead to a better agreement than assuming a ring with constant flux.
RT models that contain large grains lead to similar inner rim positions as RT models with highly refractory grains like iron or corundum. To distinguish between the two scenarios, a detailed analysis of the visibilities is necessary. |
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Name: Kokotanekov, Georgi
Talk/Poster: Talk
Title: AGN Feedback in Galaxy Clusters at Low Radio Frequencies
Abstract:
The interaction between the central supermassive black hole and the surrounding intracluster medium has been shown to play a significant role in the evolution of galaxy clusters. Low frequency radio observations provide a unique tool to study this feedback process. In particular, they allow us to detect older, diffuse emission at larger radii and trace the integrated AGN energy output over longer timescales.
In this talk I will summarise my recent study on the Bîrzan sample of strong feedback systems observed by two low-frequency radio surveys -- MSSS and TGSS ADR1. I will discuss my results on the correlation between X-ray cavity power and radio luminosity of clusters. I will additionally focus on several particularly interesting sources in the sample.
In the second part of my talk I will present new exciting results obtained from deep radio and X-ray observations of two famous clusters - Perseus and Abell 1795. I will revisit their complicated morphology and comment on the integrated history revealed by the new observations. I will further discuss how the new radio observations of diffuse extended emission seem to challenge the classical idea of the correspondence between the radio lobes and X-ray cavities. |
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Name: Krauss, Felicia
Talk/Poster: Talk
Title: Dynamic SEDs of southern blazars
Abstract:
Active galactic nuclei often show relativistic outflows of matter, called jets. We study their simultaneous radio to gamma-ray spectral energy distributions (SEDs) from the TANAMI sample, with over 80 SEDs for 22 sources. The large amount of monitoring data from the TANAMI project allows us to construct dynamic SEDs, highlighting spectral changes in varying flux states. With the data, we can address key questions in AGN jet physics like the existence of the blazar sequence and the Fermi blazar's divide, the fundamental plane of black hole masses and the origin of the "big blue bump".
In high flux states the sources do not seem to follow the blazar sequence, suggesting a physical change in the jet. We find disagreements with the Big Blue Bump originating in thermal emission from the accretion disk. We further observe that the fundamental plane does not work well as an estimator of the black hole mass, or the black hole mass is severely overestimated by SED fitting for some of the sources. |
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Name: Lahuis, Fred
Talk/Poster: Poster
Title: Star and Planet formation with the James Webb Space Observatory
Abstract:
The James Webb Space Telescope (JWST) continues on schedule for an October 2018 launch from Kourou. Over the last year testing of the science instruments, mirror assembly, integration of the science instruments and mirror assembly into the OTIS (Optical Telescope Element and Integrated Science) all completed at Goddard. This Spring the OTIS will be shipped to Johnson for testing in the historic Chamber A. At the same time integration and testing of the spacecraft and sunshields takes place at Northrop Grumman where also the integration of the OTIS and the spacecraft and the full observatory testing will take place in 2018. Mission and science preparations are also in full swing. Early 2017 the calls for Guaranteed Time Observation (GTO) proposals and Early Release Science (ERS) Letters of Intent have come out. In my talk I will start with a brief summary of the current status of the observatory, its scientific capabilities and the project and science timelines. I will then give an overview of the (intended) star formation and exoplanet programs within the GTO and ERS programs. I hope this may trigger the imagination and open the eye to General Observer (GO) science opportunities. The GO call for proposals is due to come out on November 30, 2017 with submission on March 2, 2018. |
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Name: Laverick, Mike
Talk/Poster: Poster
Title: BRASS: The Belgian Repository of fundamental Atomic data and Stellar Spectra
Abstract:
Accurate atomic data is a vital component of almost every branch of astrophysics. All models and descriptions of stellar evolution, atmospheres, formation and internal structures are governed by the fundamental atomic data available to the astrophysical community. As such, errors and uncertainties in adopted atomic data can systematically propagate throughout the entire field of astrophysics.
The Belgian Repository of fundamental Atomic data and Stellar Spectra, BRASS, aims to take the first, crucial steps towards removing systematic errors in atomic input data required for quantitative stellar spectroscopy. We will thoroughly assess the quality of fundamental atomic data available in the largest repositories, such as wavelengths and oscillator strengths, by comparing very high-quality observed stellar spectra, taken using the Mercator-HERMES and ESO-VLT-UVES spectrographs, with state-of-the-art theoretical spectra. BRASS will offer both critically-evaluated atomic transition data and high-quality stellar spectra, spanning the entire visible wavelength range for BAFGK spectral types, via an online public interactive interface under development.
To date we have compiled atomic line transition data, for ions of up to 5+ and in the visible wavelength range, from major online repositories including NIST, VALD, and multiple data providers currently in the VAMDC portal. We have cross-matched multiple literature occurrences of atomic transitions for over 75,000 individual lines in preparation for our systematic quality assessment and revealed a significant scatter in literature log(gf) values of up to 2 dex. Almost 3000 unique atomic lines, spanning the BAFGK spectral types, have been selected for quality assessment and quality assessment work is currently underway. |
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Name: Lena, Davide
Talk/Poster: Poster
Title: Evidence for an outflow in the plane of the AGN torus in NGC 1386
Abstract:
Puzzling - but spectacular - features are present in the nucleus of NGC 1386. They pose a challenge to our understanding of active galactic nuclei and their interplay with the host galaxies. Optical integral field spectroscopy allowed to shed some light on the processes taking place in the heart of this galaxy. We found that the dominant kinematic components can be explained as a combination of rotation in the large-scale galactic disk and compact outflows along the axis of the AGN radiation cone. However, there is also compelling evidence for an outflow in the plane of the AGN torus. Is this a new clue to the physical processes operating in AGNs? |
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Name: Liska, Matthew
Talk/Poster: Poster
Title: GRMHD simulations of (ultra) thin accretion disks
Abstract:
Black hole accretion disks come in various sizes and shapes and often launch jets. One would also expect these disks to be tilted with respect to the black hole's spin. To correctly interpret observations one needs to understand for an arbitrary disk tilt the internal disk's dynamics, the jets which are produced and the interaction of the disk with its wind and jet.
In the past most of this work was done semi-analytically and considered either thin disks, where angular momentum is transported by viscous torques, or thick disks, where angular momentum is transported by waves. However this semi-analytical work was mostly done in the regime where the tilt angle is smaller than the disk's aspect ratio, didn’t take into account the disk-jet interaction and introduced approximations when treating the turbulence driven viscosity in accretion disks.
I will focus in my talk on GRMHD simulations in the thin (H/R~0.1) and ultra-thin (H/R~0.03) disk regimes for tilted accretion disk-jet systems addressing the above mentioned inaccuracies in semi-analytical work.
I will show using the highest resolution GRMHD adaptive mesh refinement simulations ever that the disk and disk wind can initially precess at different rates, which can have interesting observational consequences.
I will also show that in the ultra-thin disk regime the inner disk's angular momentum vector can align with the black hole's spin axis, supporting the presence of the (or something similar to) Bardeen-Petterson effect for ultra-thin disks tilted at up to 45 degrees. |
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Name: Lopez, Kristhell
Talk/Poster: Talk
Title: Near Infrared Counterparts of ULXs
Abstract:
The X-ray luminosities of the Ultraluminous X-ray sources (ULXs) are suggestive of intermediate mass (10^2-10^5 Msun) black holes (IMBHs) if they radiate isotropically at sub-Eddington levels as observed in stellar black holes and AGNs. To probe the mass of these sources, and determine their true nature, we are finalizing an imaging campaign, targeting ULXs within 10 Mpc. We observed the ULXs in the near-infrared (NIR) band, searching for possible signatures of red supergiant (RSG) donor stars. We have confirmed spectroscopically several M-type RSG donors, whose photospheric absorption lines can be used for radial velocity studies. We have observed 43 ULXs in the last two years, and we find NIR counterparts for 16 of them. Of these 16 ULXs, 8 have candidate counterparts with absolute magnitudes consistent with them being RSGs. We will provide an update of our most recent observing campaigns and discuss the impact on the masses of compact objects powering the ULXs with RSG counterparts. |
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Name: Lucchini, Matteo
Talk/Poster: Poster
Title: How to easily accelerate relativistic jets: a magnetically-dominated, multi-zone model
Abstract:
Accreting black holes often launch collimated, relativistc outflows of plasma called jets, which can be some of the brightest sources in the sky. Jets are observed both in X-ray binaries (XRBs) and active galactic nuclei (AGN). Understanding the launching and acceleration of these jets, and the details of particle acceleration within them, is still an open question in high energy astrophysics.
The past decade has seen a dramatic improvement in the quality of available data, particularly in the X-ray and γ-ray bands. However, the semi analytical modelling of jets has advanced very slowly, and single-zone models are still the preferred method of interpreting data, particularly for AGN. While useful in roughly constraining the properties of jets, and especially in addressing the origin of the X-ray and γ-ray emission, these one-zone models cannot fully
capture the physics of jets, which are regulated by the equations of General Relativistic Magnetohydrodynamics (GRMHD).
We present a new multi-zone jet model which computes the properties of the entire jet from its launching point across its entire length. The jet dynamics are a simple parametrization of GRMHD, in which the magnetic flux is turned into bulk kinetic energy. To benchmark the model we fit six quasi-simultaneous, multi-wavelength SEDs of the AGN PKS2155-304 obtained by the TANAMI program, and we address the degeneracies introduced by such a complex model by employing a state-of-the-art exploration of parameter space, which so far has
been mostly neglected in the study of AGN jets |
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Name: Maan, Yogesh
Talk/Poster: Poster
Title: Pulsar searches and studies: scope at frequencies below 100 MHz
Abstract:
Majority of radio pulsar searches and studies have generally utilized frequencies in the range 300--1500 MHz. However, a number of sensitive telescopes are now operating and enabling studies at frequencies below 100 MHz. At such low frequencies, detection of pulsed signals from distant sources is hindered by several propagation effects in the interstellar medium. So, blind pulsar surveys at these frequencies are generally less appealing, and targeted searches as well as studies utilizing known sources could be more fruitful. I will discuss a few strategies that could still be useful to conduct blind searches and reveal interesting sources with minimum impact on telescope time and computing resources. In the context of targeted searches and studies, I will present a summary of results from several efforts made in last few years and some from the currently ongoing work. More particularly, I will present (1) detection of decameter wavelength emission from a couple of gamma-ray pulsars that were earlier considered radio-quiet, and (2) early indications from interstellar scattering study of a sample of pulsars observed using LOFAR. |
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Name: Maccagni, Filippo
Talk/Poster: Talk
Title: Atomic and molecular absorption lines trace THE Fuelling of radio AGN
Abstract:
AGN may play a crucial role in regulating the balance between accretion and ejection of gas in a galaxy. Absorption of neutral hydrogen (HI) in radio AGN is a powerful tool to identify cold gas flowing in and out of the active nucleus and to determine the HI content in early-type galaxies. Just before Apertif was installed on the WSRT, our research group observed 250 radio sources, detecting HI absorption in 30% of them. In this talk, I will show how the HI content in radio-AGN varies according to different properties of their nuclei and their host galaxy. In this talk, I will also present the study case of PKS 1718-649. This is a young (~100 years) radio-AGN where we detect two HI absorption lines tracing gas that may fuel the central black hole. Follow-up observations of the warm H2 (2.12 μm) and cold CO in the innermost kilo-parsec of this galaxy reveal a clumpy circumnuclear ring that forms the fuel reservoir of the nuclear activity. I will show the latest results from our high resolution (0.2’’) ALMA observations of the CO 2-1. Close to the radio source, we detect a red-shifted absorption line that traces clouds accreting onto the AGN. This is the first time that accretion of cold gas is detected in such a young radio source. |
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Name: Mandal, Soumyajit
Talk/Poster: Talk
Title: LOFAR observations of the Lockman Hole field and the merging galaxy cluster ABELL 1914
Abstract:
The Low Frequency Array (LOFAR) is a powerful survey instrument and particularly sensitive to steep spectrum diffuse objects. LOFAR data processing is challenging due to the data volume and the ionosphere, which, at low frequencies, needs to be calibrated as a function of time and location.
I will present our ongoing work on the 48 hours of LOFAR observation of the “Lockman hole” which is a well studied extra-galactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). I will also present our work on the merging galaxy cluster Abell 1914 where we have analyzed LOFAR (150MHz), GMRT (325MHz and 610MHz), VLA (1.4GHz), CFHT and Chandra observations allowing us to:
1) Discover an ultra steep spectrum source (4C38.39; spectral index |
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Name: Manick, Rajeev
Talk/Poster: Talk
Title: The evolutionary nature of RV Tauri stars with a disc
Abstract:
RV Tauri stars are a group of pulsators which occupy the high luminosity end of the population II Cepheids. They are generally assumed to be in a post-AGB phase of evolution and evolving towards the PNe stage. We carried out a radial velocity study to probe the binary status of 6 such RV Tauri stars in the Galaxy. The objects were chosen to have warm circumstellar dust which is likely trapped in a disc. Our results show that all the 6 RV Tauri stars are binaries with orbital periods ranging from ~ 650 to 1700 days and eccentricities between 0.2 and 0.6. The derived mass functions point to unevolved low-mass companions. We used the pulsations to constrain their luminosities via a calibrated PLC relation and thus placed them on the HR diagram. Our derived stellar luminosities show that 4 of them are indeed post-AGB binaries but the rest are less luminous than the tip of the Red Giant Branch (RGB). We conclude that these are likely candidates of the newly discovered post-RGB objects. The evolution of these evolved star was affected by a strong phase of binary interaction. Our results also corroborate the finding that evolved stars surrounded by a dusty disc are all binaries. |
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Name: Marchetti, Tommaso
Talk/Poster: Poster
Title: An Artificial Neural Network to Discover Hypervelocity Stars: Candidates in Gaia DR1/TGAS
Abstract:
Hypervelocity stars (HVSs) are stars that can reach velocities in excess of the Galactic escape velocity at their location, and whose trajectories are consistent with a Galactic Centre origin.
The paucity of HVSs known to date has severely hampered their potential to investigate the stellar population of the Galactic Centre and the Galactic Potential, and the first Gaia data release gives an opportunity to increase the current sample.
We have applied a novel data mining algorithm based on machine learning techniques, an artificial neural network, to the TGAS catalogue. With no pre-selection of data, we could exclude immediately ~ 99% of the stars in the catalogue and finnd 80 candidates with more than 90% predicted probability to be HVSs, based only on their position, proper motions, and parallax.
Tracing back their orbits in different Galactic potential models we found one possible unbound HVS with v ~ 520 km/s, 5 bound HVSs, and, notably, 5 runaway stars with median velocity between 400 and 780 km/s.
At the moment uncertainties in the distance estimates and ages are too large to confirm the nature of our candidates by narrowing down their ejection location, and we wait for future Gaia releases to validate the quality of our sample.
This test successfully proofs the feasibility of our new data mining routine. |
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Name: Marcote, Benito
Talk/Poster: Poster
Title: On the origin of the gamma-ray binary 1FGL J1018.6-5856
Abstract:
Gamma-ray binaries are powerful systems that accelerate particles up to relativistic energies and exhibit non-thermal emission from radio to TeV, with the maximum emission located at GeV energies. These binary systems are composed of a massive star and a compact object, likely to be a neutron star in all cases.
The stellar wind interacts with the relativistic wind of the neutron star, producing a strong shock in between. The shocked material moves away from the system originating a cometary tail that precesses within the orbital motion.
Only five gamma-ray binaries are known to date, all of them with O or B spectral type stars but exhibiting a huge range of orbital periods (from 4 days to 3.4 years) and eccentricities (from almost circular to highly eccentric orbits). Detail observations of each of them produce a valuable improved on the knowledge of the whole population.
1FGL J1018.6-5856 is a gamma-ray binary composed of a O6 V((f)) star and a compact object that orbits it every 16.6 days. The source exhibits orbitally modulated emission from radio to TeV energies and is surrounded by a supernova remnant, SNR G284.3-1.8, that has been suggested to be originated by the compact object in 1FGL J1018.6-5856. Here we present the first very long baseline observations of 1FGL J1018.6-5856 with the Australian Long Baseline Array (LBA) at 8.5 GHz to study its compact emission and proper motion. These observations can clarify the possible association with the SNR and the origin of its radio emission. |
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Name: Markoff, Sera
Talk/Poster: Talk
Title: Think globally, act locally: “Altair", an outreach pilot in “de buurt” of UvA Science Park
Abstract:
I will present a pilot outreach project that I am starting, together with volunteer PhD students and an outreach manager (Alex Verkade). The project is motivated by the longterm goal of changing the demographics of incoming students at our campus to include more under-represented groups, in the wider context of improving integration into Dutch society. This is a very complex issue, thus we are starting by exploring more local solutions to see what kind of impact we can have: we would like to break down the invisible barrier between the Science Park and the people in its neighbourhood. Our first project focuses on two classrooms of Group 8 children at an Islamic elementary school around the corner from our campus. We named the project “Altair” to emphasise the contributions to astronomy from the Islamic world during it’s “golden” age. Working together with the head of school and head of activities, we have developed a plan for three visits to the school for in-classroom activities, followed by a final visit by the classrooms to the Science Park, to take place over the month of May. I will describe the original plan, and report on its implementation after two of the in-class visits. I would be very interested in exchanging ideas both for this project as well as for the future, in which we hope to bridge from this project to activities also involving the families of the initial group of children, along with continuing with the Altair project. |
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Name: Maseda, Michael
Talk/Poster: Talk
Title: JWST science is (really) just around the corner
Abstract:
JWST is scheduled to be launched in October 2018, and will provide new observational capabilities relevant for all areas of astronomy. The first call for proposals will be issued this year. We present the current status of the mission, and discuss the schedule for proposal submission and selection, and the relevant policies. |
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Name: Massari, Davide
Talk/Poster: Talk
Title: The power of teaming up HST and Gaia: proper motions for distant star clusters and dwarf galaxies.
Abstract:
The Hubble Space Telescope (HST) and the Gaia mission are two exceptional instruments for precise astrometry and proper motion measurements. However, they do have some limitations by themselves. HST often lacks suitable multi-epochs observations, and even at the end of its mission Gaia will provide proper motion measurements based on a temporal baseline of only 5 years.
The combination of data from HST and Gaia allows one to overcome both these limitations, and to do so already now, with the exploitation of Gaia data release 1. This first release lacks proper motion measurements for sources fainter than magnitude 12, but combined with HST images taken many years ago it is already very powerful.
In this talk I will present the first succesful attempt to combine HST and Gaia to measure the proper motion of the distant globular cluster NGC2419, at 90 kpc, for the first time. By coupling this measurement with the cluster radial velocity, we have reconstructed the orbit of NGC2419 and discovered that it is very likely a former cluster of the Sagittarius Dwarf Spheroidal Galaxy. It must have been lost very soon after Sagittarius entered the potential well of the Milky Way. This intriguing result is a fundamental piece of information necessary for the accurate reconstruction of the remarkable history of the Sagittarius dwarf galaxy and its interaction with the Milky Way.
Finally, the application of our method to more challenging dwarf galaxies, and the related preliminary results, will also be discussed. |
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Name: Michilli, Daniele
Talk/Poster: Talk
Title: The physical processes behind Fast Radio Bursts
Abstract:
Fast Radio Bursts (FRBs) are millisecond-duration radio flashes of
extragalactic origin. There are around 20 FRBs detected to date and
only one has been observed to repeat so far. Its repetition permitted
to localise it within a dwarf galaxy at z=0.19. However, the emission
mechanism and even the nature of the object producing such powerful
bursts are still a mystery. Characteristics of the repeating FRB can
be inferred by studying the proprieties of the emitted bursts. For
this reason, we performed an intensive observing campaign with the
Arecibo telescope during the last 2 years. Using a coherent
dedispersion technique we could reach a time resolution never before
possible. We are performing a systematic study of the burst
statistics with the aim of putting constraints on the emission
mechanism. In this talk, I will review some of the most informative
proprieties that we are finding. Among these, the absence of a
secular variation in the source dispersion measure excludes supernovae
younger than few decades around the central object. The absence of
polarisation, the burst rate and the frequency structure of the bursts
are other examples of informative characteristics that are being
studied. By collecting this information, we will be able soon to
disfavour many of the numerous models that have been proposed to
explain FRBs. |
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Name: Mikhailov, Klim
Talk/Poster: Talk
Title: PSR J1614−2318: an aligned millisecond pulsar that accreted inefficiently?
Abstract:
Millisecond pulsars (MSPs) can produce γ-ray emission, thus suggesting targeted searches in radio toward unidentified γ-ray sources. In the search for the mid-latitude EGRET γ-ray sources with the Parkes telescope, the unrelated, non γ-ray emitting radio MSP binary PSR J1614−2318 was unexpectedly discovered. The pulsar has a nearly 100% duty cycle at low frequencies. Strangely, its very low-mass companion ($M_mathrm{c,min} = 0.095_{-0.015}^{+0.19},M_odot$) should have spun it up faster than to the current spin frequency of 30 Hz. That is not in accordance with standard evolutionary models. At the same time, the ratio between the binary orbital period and the companion mass follows theoretical predictions within the 90% error bars. From 13 years of multi-frequency radio and optical observations of PSR J1614−2318, we obtained a good understanding of its orbit. We conclude the binary evolved based on the interplay between an aligned rotation, inefficient accretion, and a possibly high-mass neutron star. We also discuss the potential multi-component profile distribution. |
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Name: Molijn, Maria Cosette
Talk/Poster: Poster
Title: Black hole or jets or what? Can CTA resolve the gamma ray emission region of Centaurus A?
Abstract:
With more than 100 telescopes in the northern and southern hemispheres, CTA will be the largest ground-based gamma ray observatory so far. The observatory finds itself currently in the pre-production phase, and the first CTA science is expected early 2020’s. The angular resolution is expected to exceed 1 arcminute for energies up to 300 TeV, enabling the study of sources with (very) high-energy emission regions that have not been resolved yet. This project aims to understand how the angular resolution of the array can be optimized, such that the scientific requirements of CTA can be satisfied. We use air shower Monte-Carlo and detector response simulations, to which we apply cuts on parameters as the number of telescopes that have detected the Cherenkov air shower, or the impact parameter of the shower core. Once appropriate cuts are determined, we model a Point Spread Function and convolve radio and X-ray images of extended sources like Centaurus A using this PSF. Where the emission of Cen A is well understood at lower energies, some very important questions have been unanswered about the (very) high energy emission. From HESS measurements Cen A is known to emit gamma rays, but due to poor angular resolution, it is still unknown whether the emission is from the black hole itself or lines up with the jets. We therefore aim to analyse to what extend regions like the lobes, jets and core of Cen A can be resolved with the CTA angular resolution. |
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Name: Montofre, Daniel
Talk/Poster: Talk
Title: Design of an Optical Beam Combiner for Dual Band Observation with ALMA
Abstract:
This project is aimed to study the feasibility, practical implementation and benefits of simultaneous multi-band beam-combined observations with ALMA, by means of external optics on a few baselines employing existing ALMA receivers. Our goal is to improve high-frequency calibration data on long baseline observations for the ALMA antennas. A dual-frequency atmospheric phase error calibration method is proposed and will be implemented by the simultaneous observation in two ALMA Bands, specifically 6 and 9, coupled by means external optics in a few baselines. This method is envisioned to demonstrate the advantage of receiving signals simultaneously at different frequencies from the same point of the sky. It will permit an increase of accuracy in determining the phase correction needed to reduce the effects of the atmosphere. While maintaining the existing receiver optics, an optical layout that couples Bands 6 and 9 is proposed. Here we demonstrate that very limited impact on the existing ALMA system is needed. Furthermore, we present in detail the optical layout, made within the formalism of ray optics, and a detailed tolerance analysis. The initial results demonstrate the feasibility of the proposed system. |
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Name: Murillo, Nadia
Talk/Poster: Talk
Title: Multiple protostellar systems: Coevality and structure
Abstract:
Multiple stars are invaluable stellar physics laboratories and produce interesting phenomena in evolved stars, such as spiral dust and gas shells, type Ia supernovae, and one of the mechanisms to form binary black holes. Observations of protostars show that multiplicity is ubiquitous throughout all stages and masses of the star formation process. Additionally, multiplicity is more frequent in the earliest phases of star formation compared to the later pre-main sequence stages. Thus, multiple stellar systems are born. However, we still have much to learn about when and how multiple protostars are formed, and their evolution. Low-mass star forming regions are ideal for studying the birth and evolution of these systems, due to their proximity and less crowded environments in comparison to high-mass star forming regions. Two key questions that need to be addressed are: Which formation mechanisms produce what kind of systems? Which evolutionary paths and physical factors shape these systems? Therefore we study when and how multiple protostars are formed by establishing the relative evolutionary stages, i.e. coevality, of each component in the system. The physical structure of a protostar needs to be determined in order to understand the evolutionary path it may take. In a multiple protostellar system, relating the coevality to the physical structure of the whole system is needed to understand how the multiple protostar forms and evolves. In the presented work, multiwavelength observations and models are combined to answer the questions of multiple protostellar system formation and evolution. |
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Name: Navarro, Ramon
Talk/Poster: Talk
Title: Overview of optical and infrared instrumentation in The Netherlands
Abstract:
Last year we had a special E-ELT session at NAC.
Please let me know what would be appropriate this year.
I'm thinking to give an overview presentation of all optical and infrared instrumentation activities in The Netherlands.
Of course this depends on, and is adaptable to, possible other instrumentation talks. |
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Name: Nelemans, Gijs
Talk/Poster: Poster
Title: Science with the Einstein Telescope, SKA and LISA
Abstract:
The future of gravitational wave astronomy is bright due to the planned next generation facilities: the Einstein Telescope, SKA and LISA. I will discuss the current results of the ground based experiments and the exciting possibilities for astrophysics with multi-wavelength gravitational-wave astronomy. |
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Name: Nobels, Folkert
Talk/Poster: Poster
Title: Quantifying the star formation history and stochasticity in early galaxies
Abstract:
Over the past few years, instruments such as the Hubble Space Telescope have provided tantalising glimpses of a time when the earliest galaxies were just assembling in an infant Universe. The large volumes surveyed and significant number statistics collected provide an unprecedented opportunity to study the key physics driving the assembly of such systems. We use a semi-analytic theoretical model that captures the key physics of supernova and reionization feedback in ejecting gas from low-mass halos, and tracks the resulting impact on the subsequent growth of more massive systems via halo mergers and gas re-accretion in early galaxies at z~5-20. We use this model to quantify, both, the star formation histories and their stochasticity in early galaxies. |
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Name: Oomen, Glenn-Michael
Talk/Poster: Talk
Title: Exploring the orbital diversity of post-AGB binaries
Abstract:
We present a homogeneous analysis of all orbital elements available for post-AGB stars (some 40 systems). These objects are in a transition phase to become a hot central star that will ionise material that is expelled near the end of the AGB. All our systems evolved to long-period binaries (100-2000 days) and often with non-zero eccentricities. This comes as a surprise as these binaries are expected to strongly interact when the progenitor is in the AGB phase. Mass transfer for an AGB star is always unstable. Models predict that this results either in post-common envelope systems (P < 10 days), or in systems that barely interact (P > 10000 days). However, the observed systems seem to have exactly the periods which are least predicted.
All post-AGB binaries harbour a circumbinary disc formed by interaction with the companion during the phase of intense mass loss by the AGB star. Metal-poor gas from the disc is reaccreted onto the post-AGB star, causing depletion of refractory elements. In this contribution, we investigate how strong accretion can affect the evolutionary timescale. The goal of this work is to evaluate whether feedback from a disc can impact the post-AGB evolution. |
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Name: Oostrum, Leon
Talk/Poster: Poster
Title: Multi-messenger follow-up of radio transients from ALERT
Abstract:
The Apertif upgrade to the Westerbork radio telescope has equipped 12 of the telescopes with phased array feeds operating at 1.4 GHz. The ALERT (Apertif LOFAR exploration of the Radio Transient Sky) survey will begin later this year and make use of this new system to search for Fast Radio Bursts and other radio transients in real-time, providing arcminute localization. A triggered detection with LOFAR could further refine this to arcsecond scales. For succesful multi-wavelength follow-up of radio transients, fast and accurate localization is key. I will give an overview of our current follow-up strategy, which involves multiple telescopes spanning the whole electromagnetic spectrum as well as multi-messenger detectors. |
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Name: Orosz, Gabor
Talk/Poster: Talk
Title: Water fountains and the shaping of planetary nebulae using maser VLBI
Abstract:
One of the pivotal questions in stellar evolution is how to explain the formation of planetary nebulae, whose morphology depart significantly from spherical symmetry. There is a lot of observational evidence that the asymmetric shaping of the circumstellar envelopes of evolved stars is already well under way prior to photoionization. Water fountains are evolved stars that host high-velocity water masers that trace the shocked regions of bipolar outflows, which seem to be key objects to better understand the changes in the mass-loss modes prior to the planetary nebula stage. Here we present the most recent results of our VLBI water fountain projects, which we use to illustrate the water fountain phenomenon, describe the shocked regions immersed within the outflows, obtain information about the host star and its environment, and discuss the implications on stellar evolution. |
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Name: Pabst, Cornelia
Talk/Poster: Talk
Title: Velocity-resolved [CII] mapping of the Orion Molecular Cloud
Abstract:
Velocity-resolved [CII] 158 mu observations are an excellent tool to study the interplay of gas and stars, the way the interstellar medium (ISM) is shaped by stellar radiation. [CII] emission as a main coolant of the ISM mainly arises from the surface of a molecular cloud, so-called photodissociation regions (PDR), where the stellar UV radiation impinges on the cloud. From the emission properties, e.g. intensity, spatial distribution and line profile, we can trace a variety of properties of the [CII]-emitting ISM: the heating-cooling balance, correlation with other gas and dust tracers and with the physical properties (e.g. density and temperature), as well as the global velocity structure of the cloud and turbulence within the gas. As of now, the airborne observatory SOFIA is the only facility capable of observing [CII] emission from the nearby universe, providing a unique view on the shaping of the ISM. Understanding [CII] emission from nearby sources is vital for the [CII] line to be employed as a tracer of star formation in distant galaxies with ALMA. We studied velocity-resolved [CII] emission observed with upGREAT onboard SOFIA in the Orion Molecular Cloud, a region of 210 square arcsecs of L1630 in the Orion B complex, comprising the iconic Horsehead Nebula, and recently an area of 1.25 square degrees in the Orion A complex, covering the Orion Nebula. We present our (preliminary) insights into the cloud structure and properties gained from [CII] observations in these two regions. |
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Name: Papastergis, Manolis
Talk/Poster: Talk
Title: Are the small-scale cosmological challenges of LCDM resolved?
Abstract:
The LCDM paradigm has been facing a number of observational challenges on the small scales associated with the formation of dwarf galaxies (~1 kpc). Recently, significant progress has been made thanks to the advent of sophisticated hydrodynamic simulations of galaxy formation. These simulations have demonstrated that baryonic feedback can have a profound impact on the observable properties of dwarfs, and could potentially explain the apparent discrepancies between LCDM predictions and observations.
In my talk, I will review the present observational and theoretical status of the small-scale cosmological challenges to the LCDM paradigm, focusing primarily on the pressing "too big to fail" (TBTF) problem. I will briefly discuss the most promising baryonic solutions to TBTF, and assess the degree to which they have been successful in resolving the issue. I will then present a new potential astrophysical solution to TBTF, involving the complexity of the baryonic kinematics in the shallow potential wells of dwarfs (Verbeke,Papastergis+ 2017). I will conclude by describing the next steps that are needed to validate observationally all proposed astrophysical solutions that rely on efficient stellar feedback (e.g., supernova feedback, radiation feedback from OB stars, etc.). |
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Name: Paragi, Zsolt
Talk/Poster: Talk
Title: Fast Radio Burst 121102 localization with the EVN
Abstract:
The key to understand the fast radio burst (FRB) population is accurate sky localization. FRB121102, the only known repeater so far, was recently localized with the Jansky Very Large Array (VLA) on 100 milliarcsecond (mas) scale; this was further refined with the European VLBI Network (EVN) to 12 mas. The host is a metal-poor dwarf galaxy at a redshift of 0.1927, with a compact persistent radio source of unknown origin, co-located with FRB121102. The VLBI observations place a strong constraint on the separation of this radio source and the origin of the radio bursts, which is less then 40 pc.
These observations provide strong evidence for a direct physical link between FRB121102 and the compact persistent radio source. A burst source associated with a low-luminosity active galactic nucleus or a young neutron star energizing a supernova remnant are the two scenarios for FRB121102 that best match the observed data. |
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Name: Pedersen, May Gade
Talk/Poster: Talk
Title: Unraveling the internal mixing processes of the chemical factories of the Universe
Abstract:
Without the evolution of massive stars, life as we know it on earth would never have had the chance to exist. These stars evolve tens to thousands of times as fast as stars like the Sun and are responsible for the production of the majority of the elements heavier than helium, as well as the chemical enrichment of their environment through stellar winds and supernovae explosions. During ~90% of their evolution, massive stars are highly influenced by internal mixing processes occurring in and near their convective cores such as convective core overshooting. Unfortunately, our understanding of these processes is poor and the number of useful test cases limited. Internal mixing processed therefore provide the largest uncertainties in stellar structure and evolution models for massive stars.
Asteroseismology, the probing of stellar interiors using the pulsations of the stars, offers the tools we need to constrain such internal mixing processes. Gravity modes (g-modes) in particular have considerable amplitudes throughout the entire interior of the star and are highly sensitive to the amount of mass in the overshoot layer. The value of and deviations from uniform period spacings of such modes provide information on mixing processes just above the core. With this talk we aim to show and explain how different descriptions of the convective core overshooting influences the evolutionary models and the shape of the theoretically predicted period spacing series, and what we can learn by studying such series. |
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Name: Petrillo, Enrico
Talk/Poster: Talk
Title: Finding strong lenses with convolutional neural networks
Abstract:
Gravitational lenses are rare and valuable sources that are hard to find in the volume of data produced by wide-field surveys.
I present a strong lens finder based on a Convolutional Neural Network (CNN).
I applied it to ~21789 Luminous Red Galaxies selected from 255 square degrees of the Kilo Degree Survey (KiDS). The CNN retrieved 761 strong-lens candidates. We down-selected this sample to the 22 most reliable candidates.
A conservative estimate based on this results shows that it should be possible to find ∼100 massive LRG-galaxy lenses at z |
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Name: Raaijmakers, Geert
Talk/Poster: Poster
Title: Non-idealized Mass-Radius Posteriors: Implications for EOS inference and observing strategy
Abstract:
The dense matter equation of state of a neutron star is still poorly constrained, but with the coming of future large area hard X-ray telescopes the number and precision of neutron star mass and radius measurements will increase, offering the possibility to infer this EoS from the data. In order to do so we parameterize the EoS with a three-piece polytrope with fixed matching points at three fiducial densities, leaving the pressures at these densities as free parameters. Using the Tolman-Oppenheimer-Volkoff equations we can then transform between the equation of state parameter space and the neutron star mass-radius space, thereby requiring at least three neutron stars for the transformation to be fully constrained.
Starting with three simulated, idealized Gaussians as mass-radius posteriors we use Bayesian inference to calculate the probability distribution of the EoS parameters. We then investigate the effect different variables have on this probability distribution, such as the size, shape and number of neutron star mass-radius posteriors, as well as the location of the posteriors in the parameter space. Furthermore we extend our calculations by adding a fourth neutron star and see how this affects the probability distribution of the EoS parameters. After obtaining these results we hope to propose an optimized observing strategy that will lead to the most interesting constraints on the nuclear physics of dense matter. |
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Name: Rab, Christian
Talk/Poster: Talk
Title: The chemistry of episodic accretion. 2D radiation thermo-chemical models of the post-burst phase.
Abstract:
Episodic accretion is an important process in the evolution of young stars and
their environment. A consequence of an episodic accretion event are observed
strong luminosity bursts which can last for 100s of years. The most prominent
example showing such a burst is FU Orionis. However, it is yet unclear if all
young stars experience such strong accretion bursts.
Those bursts, which mainly heat the protostellar environment, likely have a long
lasting (up to 10 000 years after the burst) impact on the chemical evolution
of the disk and envelope of young stars. Such chemical signatures open up the
possibility to identify targets that experienced a recent luminosity burst long
after the burst has ended.
We present a new model for the chemistry of episodic accretion based on the two
dimensional, radiation thermo-chemical disk code ProDiMo. For a representative
Class I model, we calculate the chemical abundances in the burst and post-burst
phase and produce synthetic observables like intensity maps and radial intensity
profiles.
During a burst many chemical species sublimate from the dust surfaces. In the
post-burst phase these molecules freeze-out again. The freeze-out happens from
inside-out as the densities closer to the protostar are higher than farther
out. This inside-out freeze-out produces clear observational signatures in
spectral line emission, like rings and distinct features in the slope of the
radial intensity profiles. Based on synthetic observations (ALMA simulations),
we propose a new model-independent method to identify post-burst objects
from C18O line images. |
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Name: Ramírez Tannus, María Claudia
Talk/Poster: Talk
Title: A lack of massive short period binaries in M17
Abstract:
The radial velocity dispersion measured for 12 massive young stellar objects in the 0-1 Myr old cluster M17 is strikingly low. This can be explained by a very low binary fraction (fbin=0.12) or a lack of short period binaries (Pcutoff>9 months), or by a combination of both scenarios. These findings are at odds with observations of 2-3 Myr old clusters. We hypothesize that massive stars are born at large separations and harden their orbits at a later stage, but within a few Myrs. If this is true, this would place important constraints on the formation mechanism of close massive binaries. |
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Name: Rapisarda, Stefano
Talk/Poster: Talk
Title: Propagating fluctuations in black hole X-ray binaries
Abstract:
Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of Black Hole X-ray Binaries (BHBs). However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and a quasi-periodic oscillation (QPO). In this scenario, because of propagation, the emission from different regions of the disc/hot flow geometry is correlated. In our study we applied the model PROPFLUC on different BHBs (including XTE J1550-564 and Cygnus X-1) in different spectral states, fitting jointly the power spectra in two energy bands and the cross-spectrum between these two bands. This represents the first study to utilize quantitive fitting of a physical model simultaneously to observed power and cross-spectra. For the case of XTE J1550-564, which displays a strong QPO, we found quantitative and qualitative discrepancies between model predictions and data, whereas we find a good fit for the Cygnus X-1 data, which does not display a QPO. We conclude that the discrepancies are generic to the propagating fluctuations paradigm, and may be related to the mechanism originating the QPO. |
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Name: Ridden-Harper, Andrew
Talk/Poster: Poster
Title: First insights from a new model of the dust tails of disintegrating rocky exoplanets
Abstract:
I will present the first results of a new model of the dust tails of disintegrating rocky exoplanets that is coupled with the ray-tracing code MCMax3D to generate transit light curves.
We find that the transit depth can be wavelength dependent or independent depending on whether the mass loss from the planet is respectively low (resulting in an optically thin tail) or high (resulting in an optically thick tail). This may help to explain why only some observations show a wavelength dependence in transit depth.
Furthermore, the height of the tail above and below the orbital plane depends on the velocity with which dust particles are ejected from the planet. For an optically thick tail, the transit depth depends on the transiting cross-section of the tail which is proportional to the height of the tail and hence the particle ejection velocity. This allows the particle ejection velocity to be constrained, giving us a deeper insight into the particle ejection mechanism and the broader physical interpretation of these enigmatic objects. |
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Name: Rivero Gonzalez, Jorge
Talk/Poster: Talk
Title: Astronomy Pre-tertiary Education at Leiden Observatory: Beyond Universe Awareness
Abstract:
During the last decade, Leiden Observatory’s Astronomy & Society Group has built up tremendous experience in managing and disseminating European and global astronomy education programmes.
Its most well-known initiative is the educational programme Universe Awareness (UNAWE), founded in 2006. Until the advent of UNAWE, there were no large-scale attempts to use astronomy as a tool for inspiring and educating young children. UNAWE, aimed at children aged 4 to 10 years, has established a consolidated network in 61 countries that has reached 400,000 children so far and produced over 10,000 inquiry-based learning educational resources including the Universe in a Box or the Earthball.
However, the activities of the Group expand beyond the UNAWE programme. For instance, the Space Awareness project, which uses the excitement of space missions to engage children and teenagers with science and technology, has developed hundreds of educational resources based on a study to identify entry points for space in the curricula of 10 countries in Europe and South Africa.
Other initiatives include the open-access platform for peer-reviewed astronomy education activities IAU astroEDU, citizen science projects as well as the development of open learning spaces for STEAM education to foster sustainable development of local communities.
The talk will provide an overview of the astronomy educational projects carried out by the Astronomy & Society Group at Leiden Observatory, discussing details about implementation, impact, evaluation, lessons learnt and sustainability. |
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Name: Roelfsema, Peter
Talk/Poster: Talk
Title: SPICA - a cryogenic infrared space telescope proposed for ESA/M5
Abstract:
The infrared wavelength domain allows measurements to directly assess the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern formation evolution of planets, stars and galaxies over cosmic time. Infrared space missions to date were hampered by either having a warm or a relatively small size telescope, limiting the practically achievable sensitivity, limiting the research to only the brighter objects in the nearby universe.
SPICA has been proposed as an ESA/M5 candidate to take the next step in mid- and far-infrared research, by combining a large -2.5 meter- cold - < 8K - telescope with instruments employing modern ultra-sensitive detectors. Rather than using liquid cryogen, a combination of ‘V-grooves’ to provide passive cooling and mechanical coolers will be used to cool both the telescope as well as the instruments and thus the mission lifetime can extend significantly beyond the required 3 years.
SPICA will provide spectroscopic capabilities at a uniquely high sensitivity of ~3 10^-20 W/m^2. The instruments offer resolutions ranging from R~50 through 3000 in the 17-230 micron domain as well as R~30.000 spectroscopy between 12 and 18 micron. Additionally, efficient 17-35 micron broad band mapping, and small field spectroscopic and polarimetric imaging in the far infrared will be supported.
The extreme spectroscopic sensitivity will give at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance entirely new domains in infrared astronomy become accessible. |
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Name: Roelofs, Freek
Talk/Poster: Talk
Title: Expanding the Event Horizon Telescope into Africa and space
Abstract:
In April 2017, the Event Horizon Telescope (EHT), consisting of 8 stations across the globe observing at 1.3 mm, performed the first observations that could lead to an image of supermassive black holes Sgr A* or M87 on event horizon scales. Detecting and measuring the black hole ``shadow'' imprinted on the accretion flow by gravitational lensing will provide a unique opportunity to test general relativity and various accretion models. However, in order to produce razor-sharp images and put strong constraints on these models, the current EHT array should be expanded. We have performed simulated observations showing that adding the future Africa Millimetre Telescope (AMT) in Namibia will significantly increase the image quality. In particular, as we average our data over multiple epochs in order to filter out temporal variability caused by accretion flow dynamics and interstellar scattering, the image quality will be primarily determined by the uv-coverage of the array rather than the signal-to-noise ratio at the individual stations. This causes the added value of the AMT and its long east-west baselines to be comparable to key high-sensitivity EHT stations such as ALMA and the LMT. For the longer term, in collaboration with ESA we have explored the idea of performing VLBI in space, allowing us to observe at even shorter wavelengths and significantly increase the maximum baseline length. Our simulations show that in combination with the dense uv-coverage generated by two satellites in slightly different orbits, this could lead to an even sharper image of the black hole shadow. |
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Name: Rouco Escorial, Alicia
Talk/Poster: Talk
Title: The ambiguous low luminosity plateau phase in the Be/X-ray transient 4U 0115+63
Abstract:
I will present our Swift and XMM-Newton observations of the Be/X-ray transient 4U 0115+63, which harbors a magnetized (B~1.3x10^12G) neutron star. Swift and XMM-Newton monitored this source during its last 2015 type-II outburst and its consequence decay. Surprisingly, this source did not decay all the way back to quiescence but it entered an enigmatic low-luminosity plateau phase (Wijnands & Degenaar 2016), during which its luminosity was about a factor of 10 higher than its quiescent luminosity. We have reduced and analyzed all the available Swift data and a new XMM-Newton observation during this plateau phase, looking for a specific explanation in the context of the three proposed scenarios for this state. We found pulsations in the XMM-Newton data, therefore the magnetospheric accretion model (in which accretion only occurs down to the magnetospheric boundary and not to the neutron star surface) can be excluded because no pulsations are expected in this scenario. An unexpected plateau phase Swift observation during which the temperature was higher and the emitting radius smaller with a significantly higher luminosity makes it difficult to clarify if the mechanism behind this phase is due to the cooling of the heated neutron star crust (heated due to the accretion of matter) or caused by the direct accretion onto the neutron star magnetic poles. I will discuss our results in the context of both models and introduce one model, the so-called “Transition Phase model”, that would explain this unusual behavior within the framework of the heating/cooling properties of a strongly magnetized neutron star. |
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Name: Rudakov, Kirill
Talk/Poster: Poster
Title: A 211-275 GHz heterodyne receiver prototype
Abstract:
We have made a preliminary design of a sideband separating (2SB) receiver for frequency range 211-275 GHz, which can be implemented for LLAMA observatory in Argentina [1]. This frequency band is expected to be a work horse of mm VLBI system for the Event Horizon Telescope[2], and for the Millimetron space mission. We expect more teclescopes will be built as part of this activity in the near future. The receiver is conceptually similar to the ALMA Band 9 2SB receiver [3,4], it will be based on single ended superconductor-insulator-superconductor (SIS) mixers connected to a waveguide RF hybrid block. The design of the single ended SIS mixer was developed using electromagnetic modeling in CST microwave studio. We use a waveguide orthogonal probe and have found optimal waveguide sizes and quarts substrate width. The mixer is based on Nb/AlN/NbN SIS junctions embedded in a Nb/SiO2/Nb microstrip line. In order to improve design stability with respect to manufacturing tolerances we will investigate extension of the 64GHz bandwidth utilizing high current density AlN barrier SIS junctions. The detailed receiver description will be presented at the conference.
[1] Large Latin American Millimeter Array, http://www.iar.unlp.edu.ar/llama-web/
[2] K. Akiyama, at al.,230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy γ-ray state in 2012.arXiv:1505.03545
[3] Hesper R., Baryshev A.M.,at al., A sideband-separating
mixer upgrade for alma band 9, in [20 ISSTT].
[4] A. Khudchenko, A.М. Baryshev, et al., Modular 2SB SIS Receiver for 600-720 GHz: Performance and Characterization Methods,TST,v7,N1,2017 |
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Name: Russell, Thomas
Talk/Poster: Talk
Title: The reproducible radio outbursts of the dwarf nova SS Cygni
Abstract:
Jets are powerful, collimated outflows that are a ubiquitous phenomenon in accreting compact objects, from black holes, to neutron stars and white dwarfs. While jet production appears to be fundamentally related to the process of accretion, at present, how relativistic jets are produced is not well understood. Radio wavelengths provide key insights into the mechanisms responsible for accelerating electrons, including jets and outflows. In this talk, I will present the results from an intensive radio observing campaign of the dwarf nova SS Cygni, spanning multiple outbursts these observations imply synchrotron emission from a transient radio jet. By comparing the radio light curves from multiple outbursts, we can see that this system exhibits reproducible radio outbursts that do not vary significantly between outbursts. Contemporaneous optical and X-ray observations also show that the jet emission appears to switch on at the same time as disc material first reaches the boundary layer around the white dwarf, raising the possibility that the vertically-extended boundary region is necessary for the production of radio jets in accreting white dwarf systems. |
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Name: RUTTEN, Rob
Talk/Poster: Poster
Title: The Sun with ALMA
Abstract:
ALMA started solar observing in December after earlier feasibility tests. ALMA is expected to become a game changer in solar chromosphere physics because the main opacity sources are free-free hydrogen continua which obey LTE strictly in their source function and so make ALMA a direct solar thermometer, whereas all other chromospheric diagnostics are strongly scattering NLTE lines. Extensive numerical simulation studies have predicted what ALMA will
see.
However, I pose that reality will be much more interesting: instead of the predicted well-known acoustic shocks below the chromospheric fibril canopy observed in Balmer-alpha, ALMA will sample this canopy as an opaque blanket and is likely to diagnose the yet unidentified small momentary propagating heating events that produce it.
I will explain the non-equilibrium formation of hydrogen diagnostics underlying this prediction. The culprit is Lyman-alpha. It is the most scattering line in the solar atmosphere but yet reaches LTE in hot instances, followed by gigantic (10^15) non-equilibrium hydrogen-top overpopulations in subsequent cooling. These define
Balmer-alpha and the mm continua observed with ALMA.
References: 2017A&A...597A.138R, 2017A&A...598A..89R, 2016arXiv161105308R. |
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Name: Saikia, Payaswini
Talk/Poster: Talk
Title: 1.4 GHz FIRST Radio flux on the Optical Fundamental Plane of Black Hole Activity
Abstract:
Black hole accretion disc and its associated jets form a coupled system, which is thought to scale globally across the entire black hole mass range - from the stellar mass X-ray Binaries to the supermassive Active Galactic Nuclei. Using a sample of 39 low-luminosity AGN selected from the Palomar Spectroscopic Survey and the 4 best-studied stellar mass X-ray binaries in the low/hard state, we report the discovery of a fundamental plane of black hole activity in the optical band, with the nuclear [OIII] emission line luminosity as a tracer of accretion rate. We study a large sample of 10149 AGN on the optical fundamental plane, obtained by cross-correlating the AGN samples in SDSS survey and 1.4 GHz VLA FIRST catalogue. We show that 1.4 GHz FIRST fluxes do not trace pure AGN nuclear activities, and is rather heavily contaminated by environmental and other non-nuclear factors. We conclude that 1.4 GHz VLA FIRST fluxes do not trace the instantaneous nuclear radio emission and should not be used on the fundamental plane and other studies of AGN nuclear activity. |
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Name: Saladino, Martha Irene
Talk/Poster: Talk
Title: Wind mass transfer in binaries and its effect on orbital evolution
Abstract:
Wind mass transfer is a common phenomenon in low-mass binaries containing asymptotic giant branch (AGB) stars, as a result of the slow (5-30 km/s) and dense stellar winds in this phase of evolution. In binary evolution theory these winds are usually treated as isotropic, predicting a gap in the orbital period distribution of post-AGB binaries between 1-10 yr. However, observations show that most post-AGB binaries in fact have periods in this range. This indicates that strong interaction between the wind and the orbit must have occurred. We perform hydrodynamical simulations to model wind mass transfer in binary systems where one of the stars is an AGB star. We investigate the amount of material gravitationally accreted by the companion star and the amount of material lost from the system as a function of the terminal velocity of the wind. We also determine the specific angular momentum of the material lost from the system, and use this to predict its orbital evolution. Preliminary results show that the interaction with the companion star is strongest at low terminal velocities. For terminal velocities larger than the orbital velocity of the system we find a Bondi-Hoyle-Lyttleton flow and we reproduce the isotropic wind mode, which leads to an increase of the orbit. On the other hand, for low wind velocities an accretion disk is formed around the companion and the angular momentum transferred to the outflowing material implies that the orbit will shrink. |
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Name: Santoro, Francesco
Talk/Poster: Talk
Title: Probing the efficiency of the AGN feedback in young radio-loud sources: the case of PKS1934-63
Abstract:
Compact, peaked spectrum radio sources are thought to represent the first stages of the evolution of radio Active Galactic Nuclei (AGN). In these objects, strong interaction between the radio jets and the host galaxy Inter Stellar Medium is usually observed in the form of fast outflows. Due to the lack of knowledge of the physical conditions in the outflows their impact on the host galaxies have not been properly quantified until now.
I will present the results obtained from X-Shooter observations of PKS1934-63, a compact GigaHertz Peaked Source where the ionised gas shows a complex and disturbed kinematics. Interestingly, the emission lines show multiple components including a broad (FWHM~850 km/s) component centred close to the systemic velocity and a very broad (FWHM~2500 km/s) blueshifted (v~-400km/s) component. Both the components can be related to the interaction between the central young radio source and its surroundings.
I will show how the use of new density diagnostic diagrams, sensitive to the high density regimes, allows us to accurately derive the densities of these extreme components and the key properties of the AGN-driven outflow (e.g. the mass outflow rate and the outflow efficiency).
Thanks to the extremely broad wavelength coverage and the good spectral resolution of X-Shooter we have also found evidence of shocks contributing to the gas ionization and we have traced the rotation of the gas close to the central Black Hole.
To conclude I will present our plan to extend this study to a bigger sample of young radio sources. |
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Name: Saxena, Aayush
Talk/Poster: Talk
Title: Modelling the luminosities and sizes of radio sources: radio luminosity function at redshift 6
Abstract:
We present a model to predict the luminosity function for radio galaxies and their linear size distribution at any redshift. The model takes a black hole mass function and Eddington ratio distribution as input and tracks the evolution of radio sources, taking into account synchrotron, adiabatic and inverse Compton energy losses. We test the model at z=2 where plenty of radio data is available and show that the radio luminosity function (RLF) is consistent with observations. We are able to reproduce the break that separates locally the FRI and FRII-type sources. Our predicted linear size distribution at z=2 matches the observations too. We then implement our model at z=6 and predict a RLF and linear size distribution, as this is the epoch when radio galaxies can be used as probes of reionisation. We demonstrate that higher inverse Compton losses lead to shorter source lifetimes and smaller sizes at high redshifts. The predicted sizes are consistent with the generally observed trend with redshift. The predicted RLF at z=6 is consistent with the observed decline in space densities of optical quasars. Finally, we predict the detection of 0.23, 0.022 and 0.002 z>6 sources per sq. degree at flux density limits of 0.1, 0.5 and 3.5 mJy. The paper highlighting these findings has been submitted after addressing referee comments to MNRAS and would be published soon. |
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Name: Schulz, Robert
Talk/Poster: Talk
Title: The parsec-scale outflow of neutral hydrogen gas in the radio galaxy 3C236
Abstract:
The jets of powerful radio galaxies are known to play a vital role in regulating the gas distribution of the host galaxy. Evidence for this includes observations of fast outflows of neutral hydrogen gas detected in absorption in a number of radio galaxies, though these observations mostly lacked the resolution to pinpoint the location of the outflow with respect to the jet system. However, this can be achieved by Very Long Baseline Interferometry (VLBI) and it was demonstrated for the first time in 4C12.50. Based on this, we have been conducting a study to locate and characterise the outflow of neutral gas on parsec scales in a small sample of young and recently restarted radio galaxies. Here, we will present results from a global VLBI observation of the restarted giant radio galaxy 3C236 revealing a complex gas distribution and kinematic. The improved sensitivity and bandwidth compared to previous observations enable us to recover at least part of the outflowing gas over a broad velocity range of about 600km/s and to pinpoint its location to be within 40pc of the nuclear region. We also detect diffuse gas in the region of the counter-jet lobe that is not just related to the regular rotating disk. These clouds seem to trace the gas through which the jet is travelling, thus providing constrains on the physical conditions that could be important for theoretical models. |
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Name: Shulevski, Aleksandar
Talk/Poster: Talk
Title: Giant radio galaxies in the LOFAR two meter sky survey
Abstract:
The LOFAR two meter sky survey (LoTSS) imagery is a unique data set to mine for diffuse, low surface brightness objects in the radio sky. I will showcase its potential for discovering giant radio galaxy (GRG) candidates by presenting novel GRGs in several LoTSS pointings and elaborate on the future impact on GRG science as LoTSS nears completion. |
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Name: Snik, Frans
Talk/Poster: Talk
Title: Looking up to the skies with our feet firm on the ground; societal applications of astronomy
Abstract:
Astronomy is a fundamental science that studies literally everything except for Earth-bound phenomena. Its purpose is essentially to satisfy mankind's curiosity, and to answer big questions about how the universe works, where the Earth and everything on it comes from, and if we are alone. The public interest in astronomy is therefore huge, and astronomers tend to talk enthusiastically about their research to anyone who will listen and even to those who will at first not listen. Within NOVA, we are actively exploring and creating novel ways of engaging with the public that go way beyond the one-way traffic of traditional science communication. I will give an overview of recent projects and experiments, including interactive guest lectures, projects dedicated to disadvantaged children (Universe Awareness) citizen science projects, and art+science collaborations. Furthermore, I will list a few examples from our group of how instrumentation developments for astronomy can also lead to applications here on Earth, e.g. for measuring air pollution and for biomedical diagnostics. |
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Name: Spingola, Cristiana
Talk/Poster: Poster
Title: Merger or jet-induced star-formation? A panchromatic analysis of a lensed radio-loud galaxy at z=3.2
Abstract:
I will present a detailed multi-band study of MG J0751+2716, a gravitationally-lensed radio-loud active galaxy at the cosmologically-interesting redshift of 3.2. This object consists of extended gravitational arcs, which are clearly detected in high-resolution optical (HST), near-infrared (Keck AO), mm (JVLA) and radio wavelengths (global-VLBI) at milliarcsecond-scales. By carrying out a pixellated reconstruction of the background source using a Bayesian grid-based gravitational lens modelling technique, we spatially locate the different emitting regions in the source-plane for the first time, the stellar population of the host galaxy and the radio core and jets. Also, from our JVLA CO(1-0) observations we found evidence for potential inflow of the molecular gas. The overall mm-to-radio SED is consistent with a dust bump associated with high levels of dust obscured star-formation.
The reconstructed source consists of two distinct optical components, separated by a projected distance of 200 pc, that differ strongly in colour. The reddest component hosting the AGN is found to be extremely compact, while the blue star-forming object is more diffuse and shows multiple brightness components. The spatial distribution of the cold molecular gas suggests a position close to the quasar component, and sheds light on the ignition mechanism of quasar activity. |
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Name: Stacey, Hannah
Talk/Poster: Poster
Title: Gravitational lensing reveals extreme dust-obscured star formation in quasar host galaxies
Abstract:
The physical connection between star formation and AGN growth is a fundamental aspect in the study of galaxy formation and evolution. However, investigating these processes in the high redshift Universe is challenging due to limitations in sensitivity and resolution of observational data. While there are previous studies revealing high levels of star formation in quasar host galaxies, these studies have inevitably focused on a few bright sources. By targeting sources that are gravitationally-lensed, intrinsic flux densities below the confusion limit of field sources can be observed. Thus, we probe lower luminosity sources, allowing us to construct a more complete sample of the quasar population. We have derived dust temperatures, dust masses, SFRs and FIR luminosities for 104 gravitationally-lensed quasars observed with Herschel/SPIRE, the largest such sample ever studied. We detect 87 (84%) of the sample with SPIRE: 82 (79%) quasars have spectra characteristic of dust emission, and we find evidence for dust-obscured star formation in at least 72 (69%). We find a median magnification-corrected SFR of 200 $M_{odot}~yr^{-1}$ and $L_{rm FIR}$ of $6.5 times 10^{11} L_{odot}$. This result is in line with current models of quasar evolution, but suggests that {it most} quasars exist in a transitional phase between a dusty star-forming galaxy and an AGN dominated system. This further indicates that AGN feedback does not quickly quench star formation in these sources. Additionally, we find no significant difference in dust luminosities between radio-loud and radio-quiet quasars, implying radio mode does not have a significant effect on host galaxy properties. |
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Name: Storm, Emma
Talk/Poster: Talk
Title: Building better models of the gamma-ray sky with SkyFACT
Abstract:
Template fitting of the gamma-ray sky has been quite successful in both understanding existing sources of emission and discovering new sources, such as the Fermi Bubbles and the GeV excess towards the center of the Milky Way. However, existing models still yield formally poor fits to the data with significant remaining residuals, which makes quantitative comparisons between different models difficult. We therefore introduce a new tool to fit gamma-ray data called SkyFACT, or Sky Factorization with Adaptive Constrained Templates. Rather than starting from fixed predictions from cosmic-ray propagation codes and examining the residuals to understand the quality of fits and the presence of excesses, we introduce additional fine-grained variations in the templates that account for uncertainties in gas tracers and the small scale variations in the density of cosmic rays. This yields high-dimensional models with approximately 100,000 parameters. We combine techniques from image reconstruction and adaptive template fitting, and use a penalized Poisson likelihood with maximum entropy regularization, along with the BFGS fitting algorithm, to efficiently handle this large number of parameters. We present results of fits to the inner Galaxy, including robust characterizations of the Galactic bulge emission and various excesses along the Galactic disk. We also highlight the potential of this tool to study puzzling aspects of the gamma-ray sky, such as the nature of the GeV excess. |
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Name: Todorov, Kamen
Talk/Poster: Talk
Title: Spectroscopy of Exoplanet Atmospheres
Abstract:
Spectroscopic characterization of exoplanet atmospheres in the past several years has achieved immense developments, especially with the onset of inverse spectral modelling, or retrieval. Transiting exoplanet spectroscopy from space and the ground has increased the amount of available data and spectral retrieval has proven to be a powerful tool for constraining the physical properties of exoplanet atmospheres as well as measuring their chemical compositions. Obtaining high signal-to-noise, and hence information-rich, spectra of transiting exoplanets is currently observationally challenging. I will present recent new results in the characterization of exoplanet atmospheres using retrieval and spectroscopic data obtained with the GMOS instrument on Gemini, as well as preparation of the launch of JWST. |
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Name: Torres, Santiago
Talk/Poster: Talk
Title: Dynamics of the Oort Cloud in the Gaia Era i: Close Encounters
Abstract:
Comets in the Oort cloud evolve under the influence of internal and external perturbations from giant planets to stellar passages, the Galactic tide, and the interstellar medium. The external perturbations are difficult to describe because the past (and future) orbit of the Sun in the Galaxy is not known. However, it is possible to identify some stellar encounters the Sun has had in the recent past or will have in near future, from observations of stars in the solar neighbourhood. Using the positions, parallaxes and proper motions from TGAS in Gaia DR1 and combining with the radial velocities from XHIP, RAVE-DR5, Geneva-Copenhagen and Pulkovo catalogues, we computed the 6D elements for the stars in the immediate solar neighborhood ( |
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Name: Trcka, Ana
Talk/Poster: Poster
Title: High redshift galaxies in the EAGLE suite of simulations
Abstract:
In previous work (Camps+ 2016, Trayford+ submitted) we developed a procedure to calculate dust-attenuated and dust emission fluxes for galaxies in the EAGLE suite of cosmological simulations (Schaye+ 2015), using the radiative transfer code SKIRT (Baes+ 2011, Camps+ 2015). We compared the results for a selection of simulated galaxies with observations in the Local Universe, finding good agreement in many areas. Employing the same post-processing procedure, we now have calculated dust-attenuated and dust emission fluxes in a wavelength range from UV to sub-mm for about 140 000 sufficiently resolved EAGLE galaxies at various redshifts up to z=6. We plan to compare these synthetic observations of high-redshift EAGLE galaxies to observed galaxies. This study will include the properties of and the relevant scaling relations for star-forming galaxies at high redshifts. By the time of the conference, we should have preliminary results available. While the ultimate aim is to improve our understanding of galaxy evolution, we hope at least to map the successes and limitations of our numerical models and to inform the design of future cosmological simulation projects. |
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Name: van Bemmel, Ilse
Talk/Poster: Talk
Title: Communicating from JIVE: a unique case for a broad audience
Abstract:
This year marks the 50th anniversary of VLBI, and the Joint Institute for VLBI ERIC (JIVE) has been a prominent member in this field for over two decades. In 2015 JIVE made the transition to become one of the first European Research Infrastructure Consortia (ERIC). As a European institute, the needs for outreach and advocacy in JIVE are notably different from most universities and NWO institutes. While still a relatively young ERIC, we are involved in efforts to expand the ERIC membership base. This does not detract from our position as the main support institute for the European VLBI network (EVN), and we are constantly seeking opportunities to add new telescopes to the network, while maintaining our leading role in technological development. The range of responsibilities that JIVE has requires a balanced outreach approach, which accommodates for the general public in the EU, peers around the world (astronomers), and policy makers. In this presentation we will discuss how we are trying to strike such a balance by shaping an outreach policy that reflects the core values and varied roles of JIVE. |
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Name: Van de Sande, Marie
Talk/Poster: Talk
Title: Determining the effect of a non-uniform AGB outflow on its chemistry
Abstract:
The chemistry in the outflow of an AGB star is dominated by its C/O abundance ratio. For C-rich stars, no O-rich species are expected in the inner wind since oxygen is locked up in CO, and vice versa for O-rich stars. However, several of these unexpected molecules have been detected. Non-equilibrium chemistry in the inner wind, caused by shocks due to the pulsating AGB star, can in most cases explain their existence and abundance. An alternative mechanism is the penetration of harsh UV photons in a non-uniform outflow.
In a non-uniform or “clumpy” outflow, which can be caused by e.g. binary interaction, interstellar UV photons can reach the formerly shielded inner wind and break up CO. Using the porosity description, we take a clumpy density distribution into account by modifying the optical depth of the outflow. The porosity description provides us with a solid mathematical framework. We explore the parameter space characterising clumpiness in our chemical model and describe its effect on the chemistry throughout the outflow. We find that our results can explain the existence of certain species in the inner wind and add to the results of the non-equilibrium models. |
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Name: van den Eijnden, Jakob
Talk/Poster: Poster
Title: What about the magnetic field? Measuring a truncated disk in the Rapid Burster
Abstract:
MXB 1730-335, more commonly known as the Rapid Burster, is an enigmatic accreting neutron star with peculiar bursting properties: it uniquely shows both the common Type-I X-ray bursts, originating from the runaway burning of accreted material on the neutron star surface, and the rare Type-II X-ray bursts. The latter originate from spasmodic accretion events, where suddenly large amounts of gas are accreted on the neutron star resulting in a burst of X-rays. Over 40 years after the discovery of Type-II bursts, it remains poorly understood what mechanism drives this erratic behaviour. However, a promising explanation was provided by the trapped-disk model, in which the neutron star's magnetic field traps the disk and the accreted gas piles up, only to swiftly accrete at once when its pressure exceeds the magnetic field strength. We test this model by analysing simultaneous NuSTAR, XMM-Newton and Swift observations of the Rapid Burster, obtained in an ambitious target-of-opportunity observing campaign in 2015. By fitting the reflection spectrum, i.e. emission from close to the neutron star that reflects off the accretion disk, we infer that the disk is truncated far away from the neutron star surface inbetween Type-II bursts. This result provides strong evidence for the trapped disk model and implies that the Rapid Burster possesses a relatively strong magnetic field for an accreting neutron star. |
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Name: Van Eylen, Vincent
Talk/Poster: Talk
Title: Dynamics of small Kepler planets
Abstract:
Eccentricity is a fundamental orbital parameter which holds information about planet formation and evolution as well as habitability. Surprisingly, many massive gas giant planets travel on highly elliptical orbits, in contrast to the orbits of solar system planets which are nearly circular. So far, the orbital shape of smaller, more terrestrial, exoplanets remained largely elusive, because the stellar radial velocity caused by these small planets is extremely challenging to measure. I sidestepped this problem by using photometry from the Kepler satellite and utilizing a method relying on Kepler's second law, which relates the duration of a planetary transit to its orbital eccentricity, if the stellar density is known. I focused on systems where the stellar density is known from asteroseismology. This approach enabled me to measure the eccentricity of planets even smaller than Earth, much smaller than what was previously possible.
I present eccentricity measurements for 74 planets in multi-planet systems, and 50 systems with a single transiting planet. The multi-planet systems are nearly circular, in full agreement with solar system eccentricities, but in contrast to the eccentricity distributions previously derived for exoplanets from radial velocity studies. The systems with a single transiting planet have significantly higher eccentricities. I relate this findings to obliquity measurements for multi- and single-planet systems. Finally, I link these findings to planet formation and evolution theory and argue that the eccentricity of systems with a single transiting planet may be related to the presence of non-transiting planets on inclined orbits. |
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Name: van Rossem, Walter
Talk/Poster: Poster
Title: Can Asteroseismology identify Merger Products?
Abstract:
Around a third of massive interacting binaries will merge during their lifetime. Identifying these merger products is difficult as they appear like blue supergiant stars. Using asteroseismology, I will see whether it is possible to identify these merger products. This is done using MESA and GYRE and by looking at their asteroseismic profiles and identifying features therein. |
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Name: van Terwisga, Sierk
Talk/Poster: Talk
Title: The ALMA Lupus disks survey: CN rings in two disks
Abstract:
The cyanide radical CN is an abundant molecule in protoplanetary disks, with line fluxes often comparable to those of 13CO.
We present 0.4'' resolution images of the CN N=3-2 transition and the 345 GHz continuum in disks around two low-mass stars in Lupus, Sz 71 (M1.5) and Sz 98 (K7), observed as part of the ALMA Lupus disk survey. In both disks, CN is distributed in a ring around the source center; they also both show evidence of continuum substructure. By combining results from the recently updated disk modelling code DALI with analysis of the dust continuum of the disks, we can conclude that the presence of CN rings is independent of the continuum substructure. Instead, they naturally arise from the competition between UV flux and gas density in the upper disk atmosphere. The CN fluxes in the Lupus disks population as a whole are also used to test our DALI models' predictions, and we discuss their implications. |
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Name: van Vliet, Arjen
Talk/Poster: Talk
Title: Cosmogenic gamma-rays and neutrinos constrain UHECR source models
Abstract:
When ultra-high-energy cosmic rays (UHECRs) travel through the universe they produce secondary neutrinos as well as photons, electrons and positrons (initiating electromagnetic cascades) in different kinds of interactions. These neutrinos and electromagnetic cascades are detected at Earth as isotropic extragalactic fluxes. The level of these fluxes can be directly predicted for any kind of UHECR model.
We developed a public astrophysical simulation framework for propagating extraterrestrial ultra-high energy particles, CRPropa 3, which is ideally suited for this purpose. CRPropa includes all relevant UHECR interactions as well as secondary neutrino and electromagnetic cascade production and propagation.
Our results show that the expected cosmogenic neutrino and gamma-ray spectra depend strongly on the evolution with redshift of the UHECR sources and on the chemical composition of UHECRs at injection. Pure-proton models with a source evolution corresponding to possible UHECR sources are already strongly constrained by both the neutrino flux measured by IceCube and the extragalactic gamma-ray background measured by Fermi/LAT. On the other hand a model optimised to provide the best fit to the UHECR spectrum and composition measured by the Pierre Auger Collaboration gives significantly less cosmogenic neutrinos and gamma-rays.
We conclude that neutrino and gamma-ray measurements are starting to constrain realistic UHECR models. With a few more years of data these measurements might be able to rule out all realistic pure-proton models. Furthermore, future neutrino experiments with sensitivities of ~10^{-8}–10^{-10} GeV cm^{-2} s^{-1} sr^{-1} in the EeV range will be able to constrain the fraction of protons present in UHECRs. |
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Name: Verbeke, Robbert
Talk/Poster: Poster
Title: Too Big To Fail is in the Eye of the Beholder
Abstract:
We test whether advanced galaxy models and analysis techniques of simulations can alleviate the Too Big To Fail problem (TBTF) for late-type galaxies, which states that isolated dwarf galaxy kinematics imply that dwarfs live in lower-mass halos than is expected in a ΛCDM universe. Furthermore, we want to explain this apparent tension between theory and observations.
To do this, we use the MoRIA suite of dwarf galaxy simulations to investigate whether observational effects are
involved in TBTF for late-type field dwarf galaxies. To this end, we create synthetic radio data cubes of the simulated
MoRIA galaxies and analyse their HI kinematics as if they were real, observed galaxies.
We find that for low-mass galaxies, the circular velocity profile inferred from the HI kinematics often under-
estimates the true circular velocity profile, as derived directly from the enclosed mass. Fitting the HI kinematics of MoRIA dwarfs with a theoretical halo profile results in a systematic underestimate of the mass of their host halos. We
attribute this effect to the fact that the interstellar medium of a low-mass late-type dwarf is continuously stirred by supernova explosions into a vertically puffed-up, turbulent state to the extent that the rotation velocity of the gas is simply no longer a good tracer of the underlying gravitational force field. If this holds true for real dwarf galaxies as well, it implies that they inhabit more massive dark matter halos than would be inferred from their kinematics, solving TBTF for late-type field dwarf galaxies. |
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Name: Verheijen, Marc
Talk/Poster: Talk
Title: Apertif - commissioning and survey science
Abstract:
Apertif is an innovative, wide-field radio 'camera', transforming the Westerbork telescope into an efficient survey facility. Operating at 21cm, it will image the distribution and kinematics of atomic hydrogen in 10^5 galaxies and produce nearly confusion-limited radio continuum maps over vast areas of the northern sky. A special-purpose backend will enable highly efficient searches for pulsars and transients. All hardware components are installed and the commissioning is in full swing. In this talk I will show some 'First Light' results, present the current state of commissioning and outline the planned surveys that will start in early 2018. |
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Name: Wang, Yanan
Talk/Poster: Talk
Title: The reflection spectrum of the low-mass X-ray binary 4U 1636−53
Abstract:
We present 3−79 keV NuSTAR observations of the neutron star low-mass X-ray binary 4U 1636−53 in the soft, transitional and hard state. The spectra display a broad emission line at 5−10 keV. We applied several models to fit this line: A gaussian line, a relativistically broadened emission line model, kyrline, and two models including relativistically smeared and ionized reflection off the accretion disc with different coronal heights, relxill and relxilllp. All models fit the spectra well, however, the kyrline and relxill models yield an inclination the accretion disc of ∼ 88◦ with respect to the line of sight, which is at odds with the fact that this source shows no dips or eclipses. The relxilllp model, on the other hand, gives a reasonable inclination of ∼ 56◦. We discuss our results for these models in this source and the possible primary source of the hard X-rays. |
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Name: Wevers, Thomas
Talk/Poster: Talk
Title: Black hole mass measurements of tidal disruption event host galaxies
Abstract:
When a star passes too close to a supermassive black hole, lurking in the centre of a galaxy, it gets ripped apart. This produces a luminous panchromatic flare, visible from gamma-rays all the way to radio wavelengths. The emission mechanism is currently unknown - but many theories exist. The mass of the central black hole in the galaxy that hosted such a tidal disruption event (TDE) is an important parameter in understanding its energetics and dynamics. We present the first homogeneously measured black hole masses of a magnitude-limited sample (down to g = 20.7 mag) of 11 optically selected TDE host galaxies in the Northern sky. The mass estimates are based on velocity dispersion measurements, performed on late time optical spectroscopic observations. The implications for the standard TDE picture, TDE rates, the emission mechanism and the potential of TDEs as tracers for low-mass dormant SMBH in future synoptic surveys are discussed. |
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Name: Wijers, Nastasha
Talk/Poster: Talk
Title: UV line absorption around galaxy groups and clusters using the EAGLE simulations
Abstract:
In the circumgalactic medium, about as much gas mass is thought to exist as in galaxies themselves. Gas also resides further out, beyond the virial radius. This gas interacts with galaxies: gas accretes onto galaxies, sometimes eventually fuelling star formation, and feedback from stars and AGN ejects gas into the circumgalactic medium and can prevent accretion from further out. Therefore, studying this gas can tell us about accretion and feedback, which is important to galaxy formation.
In order to study the warm-hot gas around galaxies, I have been predicting column densities and line emission from this gas using the EAGLE (Evolution and Assembly of GaLaxies and their Environments) state-of-the-art hydrodynamical simulations. I have found column density and covering fraction profiles around groups and clusters in the simulations. For this I have focussed on UV lines (O VI and Ne VIII) and some lower-energy ions (Si II and III). I will also look into X-ray lines, such as O VII and O VIII, as well as larger clusters in the C-EAGLE simulations (cosmological zooms around massive clusters using the EAGLE code). I will show the column density and covering fraction profiles for various ions. I hope to compare this data to observations. |
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Name: Wijngaarden, Marcella
Talk/Poster: Poster
Title: Modelling accretion heated neutron star crust cooling: The peculiar case of Terzan 5 X-2
Abstract:
The crusts of neutron stars in accreting X-ray transients can be substantially heated out of equilibrium with the core during an accretion outburst. When the accretion stops and the source returns to a quiescent state, the subsequent cooling of the crust can offer unique insights in the structure and thermal properties of the crust. The first crust cooling studies focussed on transient X-ray binaries with relatively long accretion outbursts (> 1 year) such that the crust would be significantly heated for the cooling to be detectable. Later it was shown that crust cooling can also be observed and studied in sources with more common shorter accretion outbursts. Here we present the results of applying a theoretical model to the observed cooling curve after a short accretion outburst of only ~10 weeks. In this study we use the 2010 outburst of the 11 Hz X-ray pulsar IGR J17480-2446 in the globular cluster Terzan 5 (the source is therefore also known as Terzan 5 X-2). Observationally it was found that the crust in this source was still hot more than 4 years after the end of the short accretion outburst. From our modelling we found that such a long-lived hot crust implies some unusual crust properties such as a very low thermal conductivity (>10 times lower than determined for other crust cooling sources). Alternatively, we find that the hot observed temperatures can be explained by a changing envelope composition during the short accretion outburst. We present predictions from both scenarios which can be further constrained with future observations. |
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Name: Wilby, Michael
Talk/Poster: Talk
Title: Developing the vAPP-cMWS: A hybrid optic for high-contrast imaging of circumstellar environments
Abstract:
In order to directly image rocky earth-like exoplanets in the habitable zones of the nearest stars, including Proxima Centauri b, the next generation of high-contrast imaging instruments must be able to reach planet-star contrast ratios of greater than 10^7 at angular separations smaller than 40 milli-arcseconds. However, current instruments are limited to detecting super-Jovian companions with orbital radii of typically tens of AU, more than an order of magnitude short of both requirements. This discrepancy is now motivating significant developments in the areas of coronagraph design, wavefront control, data reduction techniques and high-dispersion spectroscopy applications for high-contrast imaging.
The vector Apodizing Phase Plate (vAPP) coronagraph is a single phase-only optic capable of broadband starlight suppression and polarimetry in the optical and near-infrared, which has been shown to reach a 5-sigma contrast of 10^5 from 2.5-7 lambda/D in MagAO/Clio on the Magellan Clay telescope (Otten et al., 2017). Major advances in direct-write liquid crystal technologies (Miskiewicz et al., 2014) now make it possible to manufacture extreme phase patterns which combine the vAPP with complementary focal-plane wavefront sensing techniques such as the coronagraphic Modal Wavefront Sensor (cMWS, Wilby et al. 2017), which will enable the real-time elimination of contrast-limiting quasi-static speckles.
We will present recent developments towards the on-sky implementation of the vAPP-cMWS, including recent first-light results from the Leiden EXoplanet Instrument (LEXI) at the William Herschel Telescope, and the current status of designing a vAPP-cMWS optic for the upcoming MagAO-X instrument upgrade. |
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Name: Zari, Eleonora
Talk/Poster: Talk
Title: Mapping young stellar populations towards Orion with Gaia DR1
Abstract:
OB associations are prime sites for the study of star formation
processes and of the interaction between young massive stars with
the interstellar medium. Furthermore, the kinematics and structure of
the nearest OB associations provide detailed insight into the properties
and origin of the Gould Belt.
In this context, the Orion complex has been extensively studied.
However, the spatial distribution of the stellar population is still
uncertain: in particular, the distances and ages of the various
sub-groups composing the Orion OB association, and their connection to
the surrounding interstellar medium, are not well determined.
We used the first Gaia data release to characterize the stellar
population in Orion, with the goal to obtain new distance and age
estimates of the numerous stellar groups composing the Orion OB
association. We found evidence of the existence of a young and rich
population spread over the entire region, loosely clustered around some
known groups. This newly discovered population of young stars provides a
fresh view of the star formation history of the Orion region. |
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