Abstracts for the 71st Netherlands Astronomy Conference

There are 131 participants who submitted an abstract.

Name: Adebahr, Björn
Talk/Poster: Talk
Title: Absorption and depolarisation effects in starburst galaxies
Starburst galaxies are an important part of the overall galaxy population especially in the early Universe where gas densities where higher and starbursts more common. The prototypical galaxy M82 is the most nearby starburst and therefore an optimal laboratory for the examination of such complex environments. We detected strong thermal absorption in the starbursting central region of this galaxy, which is suspected to originate from the dense star-forming regions.
With our polarisation information we detected a magnetised bar in the star-bursting centre of the galaxy. Due to the setup of our observations we could follow the polarisation spectrum over frequency and analayse the dominant depolarisation effects. In how far these results are applicable to galaxies in the mid and early Universe is the subject of further studies combining observations from APERTIF, LOFAR, and other instruments.
Name: Allen, Bruce
Talk/Poster: Talk
Title: Direct observation of gravitational waves from the merger and inspiral of two black holes
This talk follows the annoucement made on February 11th by the LIGO and Virgo Scientific Collaborations. On September 14, 2015, we detected the gravitational waves emitted by the final few orbits and merger of two black holes. In this talk, I present the main results, as well as some of the "behind the scenes" details of the discovery and subsequent analysis. Reference: B. P. Abbott et al., Phys. Rev. Lett. 116, 061102, 2016.
Name: Arcangeli, Jacob
Talk/Poster: Poster
Title: Observations of exoplanet atmospheres
Exoplanet atmospheres are important from a planetary physics standpoint, but also from planet formation standpoint.
We can use atmosphere of exoplanets to study their nature, composition, structure and dynamics. With the current generation of instruments, chief amongst which is the Hubble Space Telescope (HST), we intend to constrain the origins of Hot Jupiters by using their metallicity as a tracer for planet formation. The metallicity trend as function of planet mass seen in the solar system is a signature of core-accretion, with increasing mass we see a decreasing metallicity, but does this hold for other planets?

The first spectroscopic phase curve of a hot jupiter, WASP-43b, has recently been obtained. These breakthrough observations led to measurements of the water abundance, metallicity and longitudinally dependent temperature pressure structure. The metallicity measurement then allows us to constrain the formation scenario of this planet. I introduce the significance of such observations and present results from new phase-curves observations obtain with HST/WFC3.
Name: Arends, Erik
Talk/Poster: Poster
Title: Rotation and accretion of young forming stars in Chamaeleon I
Young stars are inherently variable, due to processes like accretion events, disk emission, cool/hot spots and extinction events. By monitoring these stars in different wavelengths, we can disentangle the different sources of variability, giving us clues towards the ongoing events and ultimately the star formation process as a whole. For this purpose, we observe and analyse young stars (~3 Myr) in the star forming region Chamaeleon I. This cluster is located high in the Southern sky at a distance of 160 pc—making it one of the closest and best observable star forming regions—and contains mostly K and M stars. With the Wide Field Imager on ESO’s 2.2-meter telescope in La Silla, Chile we took images in the R, I, Hα and V-bands during 7 nights. We study the light curves of the 8 Chamaeleon I stars that show variability, and compare them in different bands. The period of the light curve defines the star’s rotation rate—for young stars typically a few days—and we distinguish specific signatures in the curve for each process in the star. Strictly periodic variations point to the presence of spots, whereas additional features hint towards shorter term events like accretion bursts. Other light curves show no periodicity, indicating mixed processes and long rotation periods.
Name: Arentsen, Anke
Talk/Poster: Poster
Title: Determining stellar parameters for the X-shooter spectral library
The X-shooter Spectral Library (XSL) collaboration is building a new, moderate-resolution stellar spectral library for use in stellar population models. XSL contains ~700 stars covering the entire HR diagram, each with spectra covering the large wavelength range 300-2500 nm at a spectral resolution of 7000-11000. To be useful for stellar population models, we need to derive accurate stellar parameters (e.g., effective temperature, gravity, metallicity) for the stars.

Our preference lies with using theoretical models to do this, because they are covering a much larger part of the spectrum than empirical models. A recent set of theoretical models has been developed by Husser et al. (2013). Using these PHOENIX models, we would like to find the stellar parameters by comparing model spectra to observed spectra. I investigated the possibility of using a software package called Starfish (Czekala et al. 2015) to do this comparison. Starfish is a sophisticated Bayesian code that takes into account both uncertainties in the data and the models to infer the best parameters for stellar spectra. Because some difficulties emerged, I also use a second package called ULySS (Koleva et al. 2009), which applies a more simple chi square minimization. In ULySS, different model interpolators can be used in the derivation of stellar parameters. We have tested a new interpolator for the PHOENIX models, but it seems to have some problems. Therefore, we are also using existing empirical interpolators (like for example the one derived from the MILES library) to find the stellar parameters.
Name: Barber, Christopher
Talk/Poster: Poster
Title: The origin of compact galaxies with anomalously high black hole masses
Observations of local galaxies harbouring supermassive black holes (BH) of anomalously high mass, M_BH, relative to their stellar mass, M_star, appear to be at odds with simple models of the co-evolution between galaxies and their central BHs. Theories of how such galaxies acquire such overmassive black holes include the tidal stripping of massive progenitor galaxies, or formation at very early times, when the M_BH-Mstar relation was higher, with little subsequent evolution. I will discuss how I use the EAGLE simulations to investigate first whether such galaxies are expected to form in a LCDM context at all, and if so, which formation mechanism, if either, or both, is responsible for their existence.
Name: Bartels, Richard
Talk/Poster: Talk
Title: The GeV excess: A case for millisecond pulsars
There is a clear excess in the Fermi-LAT data at energies around a few GeV. This so-called GeV-excess has attracted a lot of attention over the past years due to its remarkable similarity with the expected annihilation signal from WIMP dark matter, both in terms of spectrum and morphology. On the other hand, a large population millisecond pulsars (MSPs) living below the Fermi-LAT detection threshold are an interesting astrophysical alternative, since their prompt gamma-ray emission resembles well the spectrum of the excess. In a recent work we performed a wavelet transform of the Fermi-LAT gamma-ray data to distinguish between diffuse emission and sub-threshold point sources. The wavelet signal is significantly enhanced in the Inner-Galaxy providing corroborative evidence for the point source interpretation of the GeV-excess. In this talk I will introduce the GeV excess and make the case for MSPs based on the wavelet results. Finally, I will elaborate on the prospects of confirming the existence of a bulge population of MSPs in the near future.
Name: Bilicki, Maciej
Talk/Poster: Poster
Title: The largest all-sky galaxy catalogues and their applications
Various aspects of cosmology require comprehensive all-sky mapping of the cosmic web to considerable depths. In order to probe the whole extragalactic sky beyond 100 megaparsecs, one must draw on multiwavelength datasets and state-of-the‐art photometric redshift techniques. I will summarise our dedicated programme that employs the largest photometric all-sky surveys – 2MASS, WISE and SuperCOSMOS – to obtain accurate redshift estimates of millions of galaxies. Two catalogues have been constructed so far, and are being used for various cosmological applications. The first one – 2MASS Photometric Redshift catalogue (2MPZ) – was publicly released in 2013 and includes almost 1 million galaxies with a median depth over 300 Mpc. The second dataset, soon to be released, combines the WISE mid-infrared survey with SuperCOSMOS optical data and reaches depths over 1 gigaparsec on unprecedented angular scales. These photometric redshift samples, with about 20 million sources in total, provide access to volumes large enough to study observationally the Copernican Principle of universal homogeneity and isotropy, as well as to probe the properties of dark energy and dark matter through cross-correlations with other data such as the cosmic microwave or gamma-ray backgrounds. Last but not least, they constitute a test-bed for forthcoming wide-angle multi-million galaxy samples expected from such instruments as the SKA, Euclid or LSST.
Name: Bilous, Anna
Talk/Poster: Talk
Title: Drifting subpulses in the Bright mode of PSR B0943+10
PSR B0943+10 is one of the best examples of the rare class of mode-switching pulsars. Unlike most of the pulsar population, PSR B0943+10 has two stable modes of radio emission, each with its own distinct radio profile morphology and single-pulse behaviour. The pulsar switches between "Bright" and "Quiet" modes once every few hours and the transition takes less than a few stellar rotations. The switch in the radio modes is also accompanied by changes in the X-ray emission mode (Hermsen et al. 2013) indicating that mode switching is a rapid and global transformation of the magnetosphere and its broadband emission. The exact nature of this transformation, however, is still far from being well understood. In this talk I present results from the single-pulse analysis of the sensitive, multi-hour LOFAR observations below 100 MHz, where the frequency-dependent changes in the pulse-profile morphology are the largest, and effects too subtle to see at higher frequencies become readily evident. I report the discovery of frequency-dependent phase delay of the drifting subpulses in B0943+10's Bright mode. This effect is similar to the one reported previously for PSR B0823+26 (Hassall et al. 2013). I discuss the properties of the observed phase delay and, for the case of B0943+10, give a quantitative geometrical explanation to it within the frame of radius-to-frequency mapping theory. Finally, I will summarize the observed features of B0943+10's radio emission (both average and single-pulse) and review them in the context of polar gap conditions.
Name: Bisigello, Laura
Talk/Poster: Talk
Title: The impact of JWST filter choice on photometric redshift estimates
Choosing the right filter combination for JWST imaging observations is crucial to maximize the quality of the derived photometric redshifts in blank field surveys.
For this reason, we investigated the obtention of photometric redshift with different combination of NIRcam and MIRI (F560W, F770W) broad-band filters for three different samples of observed and simulated galaxies at z=0-10.
We found that ancillary data at ?<0.6 ?m, such as HST observations, are necessary to properly identify galaxies at z<5.5, but the MIRI F560W and F770W filters can partially mitigate the lack of short-wavelength data for the correct redshift identification. At z>5.5 the redshift estimation obtained with NIRcam alone is better than the one obtained at low-redshift because the Lyman break moves into the NIRcam wavelength range. The two MIRI bands generally improve the redshift estimation at all redshifts, particularly when used together. Due to the presence of main emission lines, the F560W filter makes a significant difference at z=7-8 while the F770W filter makes a difference at z=10. Our results constitute an important reference for the planning of all future JWST imaging surveys.
Name: Blanchard, Jay
Talk/Poster: Talk
Title: Radio-gamma ray flaring in blazar PKS 0208-512
The Fermi detected radio blazar PKS 0208-512 has shown repeated flaring behaviour at frequencies ranging from radio all the way through to the gamma-ray part of the spectrum. The physical link between such flaring is still poorly understood.
Several years of monitoring data from the TANAMI program, and supporting projects at radio, infrared/optical/UV and X-ray frequencies, as well as Fermi data have been used to investigate how large a role optical depth plays in the time delay that is commonly observed between flaring in these sources at different frequencies. Broadband spectral energy distribution modeling and jet speed calculations have also been undertaken in an endeavour to further understand the physical processes occuring in this object.
Name: Bos, Steven
Talk/Poster: Poster
Title: Determining the dynamical masses and disk sizes of the youngest protostars and proto-binary stars
We present the results of a molecular line analysis that examines the kinematics on scales < 1000 AU to characterize the disks of three single and binary young star systems (L1165, L1527 and V883 Ori). The class 0/1 object L1165 is a proto-binary and is analysed using C18O (J = 2-1), 13CO (J = 2-1) and continuum (1.4 mm) CARMA data. The class 0 object L1527 is analysed using C18O (J = 2-1) and continuum (1.4 mm) cycle 1 archival ALMA data. The class 0 FU Ori object V883 is analysed using C18O (J = 2-1) and continuum (1.4 mm) cycle 2 ALMA data. We use moments maps, PV-diagrams, Peak-PV-diagrams and a simple geometrically thin disk model in the analysis. We find for L1165 a dynamical mass of $sim$1.4 M$_{odot}$ and hints of a $sim$220 AU sized Keplerian disk. For L1527 we find the dynamical mass to be $sim$0.3 M$_{odot}$ with a Keplerian disk of $sim$60 AU, which is in agreement with the results found by Ohashi et al. (2014). Finally for V883 Ori we find a $sim$1.3 M$_{odot}$ dynamical mass and a $sim$360 AU sized Keplerian disk. These last results suggests that V883 Ori is a close analog to our Sun, and that the protostar undergoes a period of intense disk accretion, makes it a very interesting object for future studies.
Name: Bosman, Arthur
Talk/Poster: Poster
Title: Probing the inner regions of protoplanetary disks with infrared CO2 emission
Organic molecules in proto-planetary disks can be important diagnostics tools. Ro-vibrational transitions of these molecules, which are visible in the near- and mid-infrared, can probe the hot inner few AU of protoplanetary disks. They can thus trace the chemistry and physical conditions of the regions of terrestrial planet formation. These lines have been observed but have mostly been interpreted with local thermal equilibrium (LTE) models. The LTE assumption may not be valid due to the high gas densities needed to collisionally thermalise the vibrational levels.

The non-LTE excitation effects of carbon dioxide CO2 are studied to evaluate
(i) what the emitting regions of the different CO2 ro-vibrational bands are,
(ii) if and how the CO2 abundance and gas density can be traced using CO2 ro-vibrational lines.
Starting from experimental and theoretical data of level energies, Einstein coefficients and the collisional rate coefficients of CO2 a molecule model is built. The behaviour of this model is tested using non-LTE slab models. Using a 2 dimensional disk model and a radiative transfer code the CO2 line formation is modelled. This allows us to study line ratios and the 15 micron Q branch line profile. The model was tailored to the T Tauri disk AS 205(N) where CO2 is detected in the mid-infrared by the Spitzer Space Telescope.

The protoplanetary disk models suggest that the CO2 emission from protoplanetary disks comes from regions that are further out and cooler than one would infer from a LTE model.
Name: Bouma, Sietske
Talk/Poster: Poster
Title: Probing the early star formation in ultra-faint dwarf galaxy Boötes I: Zinc and yttrium
The Boötes I dwarf galaxy is one of the faintest galaxies known. The resolved stars in these small systems can help us in understanding more about galaxy evolution. For this project, I looked at high-resolution spectra from UVES for 8 red giant branch stars in Boötes I with [Fe/H] ranging from -3.7 to -2.1. Previous work has measured many elements in these spectra, but not zinc or yttrium. Using spectral synthesis, I obtained abundances and in some cases upper limits for these chemical elements. These abundances are particularly important to determine the detailed properties of the earliest stars to have formed in Boötes I. These are compared to similar stars in the Milky Way halo and in the more luminous dwarf galaxy Sculptor. From this comparison, it can be seen if there is a difference in early chemical evolution between dwarf galaxies with different mass and the Milky Way halo. The results are also compared to theoretical yields of supernovae of different mass and explosion energy to estimate the properties of supernovae that have occurred in Boötes I at various times to create the observed abundance patterns in the individual stars. Results from Y follow those in Sculptor and suggest a constant [Y/Fe] at low metallicity. Zn results follow the trend that is seen at higher metallicities in Sculptor: [Zn/Fe] increases as [Fe/H] decreases. Boötes I stars appear to show more similarity to Milky Way halo stars than those in Sculptor.
Name: Brandl, Bernhard
Talk/Poster: Talk
Title: E-ELT science with METIS
METIS is one the first three instruments on the E-ELT, expected to see first light in 2025. Apart from diffraction limited imaging, METIS will provide coronagraphy and medium resolution slit spectroscopy over the 3 - 19um range, as well as high resolution (R ~ 100,000) integral field spectroscopy from 2.9-5.3um, including a mode with extended instantaneous wavelength coverage. The unique combination of these observing capabilities, makes METIS the ideal instrument for the study of circumstellar disks and exoplanets, but also for many other areas, from our Solar system to luminous infrared galaxies at intermediate redshifts. In this presentation I will provide a brief summary of the instrument and present an overview of the exciting science that METIS will uniquely provide.
Name: Brienza, Marisa
Talk/Poster: Talk
Title: Remnant radio galaxies in the LOFAR Lockman Hole
I will present recent 150-MHz deep observations performed with the Low-frequency Array (LOFAR) of the well-known extragalactic region of the Lockman Hole. Thanks to its high sensitivity and resolution this data allows us to perform new studies of the radio loud AGN population at low radio frequencies. In particular, we conducted a systematic search of remnant radio galaxies, which represent the final “dying” phase of the radio galaxy evolution, when the jets have switched off. This class of sources is best to investigate the life-cycle of radio loud AGN as well as to quantify the role of radio AGN feedback. Indeed, the modelling of their radio spectrum provides constraints on the time-scales of activity and quiescence of the radio source and on its energy output. For a long time there have been claims that deep low-frequency surveys would have enhanced the detection of this class of sources, which are usually rare in flux limited samples.

With our search, we thus intend to provide good statistics on the detection and properties of remnant radio galaxies. To avoid selection biases towards any specific class of objects we used both morphological and spectral selection criteria. To do this we combined the LOFAR data with publicly available surveys at other frequencies as well as dedicated deep observations. We find that the fraction of candidate remnant sources is < 6-8% of the entire radio source population and is dominated by steep spectrum sources. To better understand the observed fraction we developed mock catalogues of the radio sky population based on radio galaxy evolution models. These models are used to constrain the main mechanisms contributing to the source luminosity evolution i.e. adiabatic expansion, radiative losses, as well as to make predictions on their fraction in flux limited samples.
Name: Bryan, Mark
Talk/Poster: Poster
Title: Supernova remnant RX J1713.7-3946 with the H.E.S.S. array
The shell-type supernova remnant RXJ1713.7-3946 is an exceptional observation target for the High Energy Stereoscopic System (H.E.S.S.) being bright (~0.7 crab at 1TeV) and spatially extended (0.65 degree radius). This object has been seen and measured in gamma rays, x-rays and at lower energies. The mechanism behind the gamma ray emission from this object is still debated and could prove to be key in determining the source of very high energy (VHE) cosmic rays in our galaxy.
I present results from over 10 years of H.E.S.S. observing RX J1713 with 150 hours of observation time and new analysis techniques that give unparalleled precision measurements of spectral features from 100GeV to 10TeV and morphological features on a scale smaller that 0.05 degrees.
Name: Buitink, Stijn
Talk/Poster: Talk
Title: Cosmic Ray observations with LOFAR
The detection of the radio emission from extended air showers is a fastly developing technique that complements more traditional methods. Over the last decade several experiments have measured the radio pulse properties and developed methods to reconstruct shower parameters. The extremely high antenna density of LOFAR makes it an ideal observatory for detailed studies of the emission mechanisms in air showers and the physics of cosmic rays at an energy around 10^17 electronvolt.

LOFAR has demonstrated that state-of-the-art radio simulation codes now correctly predict pulse characteristics like the power, polarization, and the complicated geometry of the radiation pattern. Therefore, the measurements can be used to reconstruct Xmax, the atmopsheric depth at which the air shower reaches its maximum. The distribution of Xmax holds information on the mass composition of cosmic rays and helps to solve urgent question about their origin, like at what energy the transition from galactic to extragalactic sources takes place.

At even higher energies, LOFAR can search for cosmic rays and neutrinos interacting in the Moon. Above 10^22 eV, these interaction produce radio pulses that are strong enough to be detected on Earth. The observational challenges resemble those of pulsar astronomy and we are now implementing a detection pipeline on DRAGNET, a GPU cluster designed for pulsar searches.

Finally, LOFAR is also exploring the interaction between cosmic rays and thunderstorms. The strong electric fields in thunderstorms leave characteristic imprints in the emission pattern that allow remote sensing of the electric field properties. We are also planning to use LOFAR to map lightning discharges and study the physics of lightning inception.
Name: Bus, Sander
Talk/Poster: Talk
Title: Interpreting the LOFAR epoch of reionization signal
In the near future a number of experiments are expected to statistically measure the redshifted 21 cm radiation emitted from neutral hydrogen during the Epoch of Reionisation (EoR). The interpretation of these measurements is probably complicated, because a number of astrophysical and cosmological components affect the EoR signal. We use a very simple Ansatz in which the power spectrum of the 21 cm emission is given as a weighted sum of the density and neutral fraction power spectra. This approximation is based on the assumption that the ionization sources are seeded at the high density regions of the intergalactic medium. Comparing the Ansatz to several (semi-)numerical simulations shows that the Ansatz works. Its use is in disentangling astrophysical and cosmological information in the EoR signal.
Name: Carbone, Dario
Talk/Poster: Talk
Title: Exploring the transient sky: From surveys to simulations
The transient sky is very important to study the dynamics of the Universe on human timescales. Transient sources are seen in every band of the electromagnetic spectrum, from low radio frequencies to gamma-ray energies, and produced by nearby flare stars to cosmological gamma-ray bursts.
We have performed a transient survey of four different fields with the LOw Frequency Array (LOFAR) at 150 MHz. LOFAR is a new generation radio interferometer which is observing at very low radio frequencies, a so far relatively unexplored frequency domain for transient searches. No credible transients were detected in our survey, but we were able to set stringent upper limits on the transient surface density using three new statistical methods. We also calculated the transient surface density as a function of the timescale of the transients, and established that the upper limits we can set vary up to two orders of magnitude for different timescales.
We have explored the complex relation between flux density, timescale and transient surface density, and developed a simulation method to calculate the transient rate as a function of both the flux and the duration of transients for different shapes of their lightcurves and for a given observing strategy. This method is independent of the nature of transient sources, and the instrument or the frequency of the observations. Therefore, this provides a tool for transient surveys carried out by current and future observatories across the electromagnetic spectrum.
Name: Carton, David
Talk/Poster: Talk
Title: Resolving metallicity gradients of intermediate redshift galaxies with MUSE
I will present results from a systematic study on the metallicity properties of (~50) intermediate redshift galaxies (0.1 < z < 1) using data from the MUSE Guaranteed Time Observing programme. With the MUSE GTO programme we are targeting galaxies across the field and group environments, observing more than 10 fields each with a minimum 10h depth. In particular I shall present results on the gas-phase metallicity gradients of galaxies in these fields. Metallicity has proven to be an especially interesting probe of galaxy evolution because it traces the effects of gas accretion and wind-driven outflows. Taking advantage of MUSE's 1'x1' FoV we are able to explore connections between the metallicity of galaxy and its local (<200kpc) environment. Owing to the limitations of seeing, little is known to date about the resolved metallicity properties of 0.1 < z < 1 galaxies. To investigate these barely resolved objects we have developed a forward modelling technique that allows us to correct for the effects of seeing upon the observed metallicity gradient. In turn this analysis has highlighted that clumpy star-formation in galaxies can produce significant scatter in the measured metallicity gradient
Name: Cendes, Yvette
Talk/Poster: Talk
Title: Tuning in the transient sky with AARTFAAC
Transient radio signals are mysterious and rare bursts of radiation from the sky, the properties of which are still largely unknown. The Amsterdam-ASTRON Radio Transient Facility And Analysis Center (AARTFAAC) is an all-sky radio monitor designed to detect these transients by taking a radio image of the sky every second. In this talk, I will present the results from the first AARTFAAC radio transient survey. This will cover describing our methods in processing the AARTFAAC data, our findings thus far including detections of meteor scatter and solar flares, and our transient rate limit from this survey. Finally, I will show a live stream of AARTFAAC-TV for a real-time demo the radio sky, and outline AARTFAAC's plans for the future.
Name: Chatterjee, Saikat
Talk/Poster: Talk
Title: Power-spectrum analysis of early-type galaxies using strong lensing
In strong gravitational lensing, by analysing the relative angular positions of the lensed images, distortions and surface brightness, we can place constraints on the mass power spectra of the foreground lens galaxy. To determine the mass power spectra of their dark matter halo, we will present a new mathematical formalism to relate lens surface brightness anomalies to the mass power-spectrum of lens galaxies. This formalism goes beyond the current linear theory. As a test we apply the theory to simulated mock lenses perturbed by a Gaussian random field potential with a prescribed power-spectrum, and subsequently we apply it to deep HST images to set limits on the power spectrum of the CDM halo around massive early-type galaxies. If time permits, I will present some preliminary results of using mock lenses as training set for Convolutional Neural Networks for the morphological classification of early-type galaxies and selecting lens candidates from the KIDS survey (or EUCLID in future).
Name: Cheng, Zheng
Talk/Poster: Talk
Title: The mass, radius, distance and cooling of the NS in EXO 0748-676 in quiescence with XMM-Newton
We present the spectral analysis of four XMM-Newton observations of the neutron-star LMXB EXO 0748-676 in quiescence, taken between 2009 and 2013. We fit the spectra with an absorbed neutron-star atmosphere model, without the need for a high-energy (power-law) component, with a 95% confidence upper-limit of 1% to the contribution of the power-law to the total flux in the 0.2-10.0 keV band. We find a significant emission line at around 0.5 keV in the spectra of the three CCD cameras on board XMM-Newton of all four observations; the line, which we tentatively identify as Lyα emission from NVII, is moderately broad, σ≈0.17 keV, and contributes 10%-14% of the total flux in the 0.2-10 keV band. The temperature of the neutron star in EXO 0748-676 has decreased significantly compared to the previous XMM-Newton observation, with the cooling curve being consistent with either an exponential decay plus a constant, a power-law or a broken power-law. We fitted the spectra with a neutron-star atmosphere model that takes into account the observed peak flux of PRE bursts to constrain the neutron-star mass, radius and distance self-consistently. Using this model we carried out MCMC simulations assuming a uniform prior for the inclination angle of the system (which accounts for anisotropy in the emission at the bursts) and for the hydrogen fraction of the fuel during the PRE bursts. We find that M=1.87+0.69/-0.32 Msun, R=8.5+3.2/-1.3 km and D=5.4+2.4 kpc (99% confidence level), which is inconsistent with quark-bearing EOS for this neutron-star.
Name: Connors, Riley
Talk/Poster: Talk
Title: Using joint spectral fitting to explore the outflow geometry of GX 339-4
The recent discovery in galactic X-ray binary (XRB) GX 339-4 of a quasi-periodic oscillation (QPO) in the infrared (IR) band as well as strongly correlated variability (with the IR lagging the X-rays by over 100 ms) suggests that variability is propagated from the accretion flow into the jets. The simultaneous, broadband (radio through X-ray) spectrum of GX 339-4 potentially provides an independent con firmation of this interpretation, because the IR is likely associated with synchrotron emission originating from scales of 1000 Rg, which is consistent with the lag. Combining spectral and timing analysis within a single study is the next step to test these correspondences. To that end we model multiple simultaneous broadband spectra of GX 339-4. We use an outflow-dominated model that can reproduce the broadband spectrum via synchrotron and synchrotron self-Compton processes (as well as a multi temperature disc blackbody component). We combine new joint- fitting techniques, adopting the use of a frequently used Markov Chain Monte Carlo (MCMC) routine, to simultaneously fit the broadband GX 339-4 datasets that are classfi ed with the same power-spectral hue - a simple one-parameter classifi er of the power-spectral state of an XRB. In this way we can reduce free parameters and see if the physical attributes driving the power-spectral state can be extracted from the fi ts, and whether this is related to other properties such as the jet break or outflow power.
Name: Croiset, Bavo
Talk/Poster: Talk
Title: Mapping PAH sizes in NGC 7023 with SOFIA
NGC 7023 is a well-known reflection nebula which shows strong emission from Polycyclic Aromatic Hydrocarbon (PAH) molecules in the form of Aromatic Infrared Bands (e.g. Berne at al., 2007; Boersma, Bregman and Allamandola, 2013). The spectral variations of the AIBs in this region are connected to the chemical evolution of the PAH molecules which, in turn, depends on the local physical conditions.
We exploited the unique capabilities of The Stratospheric Observatory for Infrared Astronomy (SOFIA) to image a 3.2' x 3.4' region of this nebula in the PAH bands with high spatial resolution (2.7"). Specifically, we look at the 3.3 um and 11.2 um emission in the north and south PDR using the PAH filter (lambda=3.3 um, bandwidth=0.09 um) of FLITECAM and the LWC filter (lambda=11.1 um, bandwidth =0.95 um) of FORCAST (PI Berne).
We compare the SOFIA images with existing images of other PAH bands (Spitzer 8.0 um), the Extended Red Emission (Hubble and Canadian French Hawaiian Telescope) and H_2 (2.12 um). We create maps of the 11.2/3.3 ratio to probe the PAH size distribution and of the 8.0/11.2 to probe the PAH ionization.
We analyze our maps with an emission model based of spectra from the NASA Ames PAH database (Boersma et al, 2014) to determine the physical conditions in the emitting regions and to understand the chemical evolution of PAH molecules in region.
Name: Crumley, Patrick
Talk/Poster: Talk
Title: Particle acceleration in mildly relativistic shocks
Shocks waves are ubiquitous in astrophysical plasmas, occuring whenever a pressure-driven disturbance travels through a fluid faster than the signal speed of the fluid. In astrophysical plasmas, nearly all shocks have widths far smaller than the mean free paths of the constituent particles of the plasma, meaning that the shock is collisionless. Collisionless shocks are capable of accelerating particles to high energies, although the acceleration mechanism is not yet understood from first principles. The main candidate for accelerating particles in shocks is diffusive shock acceleration (DSA), where particles gyrate around the shock front, diffusively scattering off turbulent fields, and gaining energy from the converging flows. I will discuss the physics of particle acceleration in shocks in a regime largely ignored in the literature, the transition between relativistic and Newtonian shocks. There many astrophysical sources that are thought to have shocks with mildly relativistic velocities: AGN, X-ray binaries, and late-time GRB afterglows. In addition, the mildly relativistic regime is a place where we expect the microphysics of collisionless shocks to be changing. Studying these shocks self-consistently requires a methodology that is capable of allowing the particles in the plasma to generate and interact with electromagnetic fields. Particle-in-cell (PIC) simulations are an ideal tool study how collisionless shocks change as they transition between relativistic and Newtonian regime. I will present preliminary results of PIC simulations of mildly relativistic shocks that show non-thermal acceleration in both electrons and ions.
Name: Daprà, M. D.
Talk/Poster: Talk
Title: First combined constraint on a varying proton-to-electron mass ratio from CO and H2 absorption
The absorption system in the line-of-sight towards quasar J1237.60+064759.5 is a unique test-case showing absorption features of both molecular hydrogen, H2, and carbon monoxide, CO, which are molecules sensitive to a variation of the proton-to-electron mass ratio, mu. The absorbing system was observed using the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph (VLT/UVES), and the wavelength calibration distortion afflicting the UVES spectrograph were addressed using the novel ‘supercalibration’ technique. More than 100 H2 transitions were used to derive a constraint on a variation of mu of the level of ~5 ppm. Some 13 vibrational CO bands are detected in the spectrum of J1237.60+064759.5: the A-X (v’= 0-8,0), B-X (0,0), C-X (0,0), and E-X (0,0) singlet-singlet bands and the d-X (5,0) singlet-triplet band. For the first time, electronic CO absorption was investigated in order to derive a constraint on a varying proton-to-electron mass ratio, mu, of ~10 ppm. This represents the first case of two independent constraint on a varying mu obtained from the same absorbing system. A combined analysis using both the molecules was performed to derive a final constraint of dmu/mu=(−0.6±5.6±3.1)×10^(−6), which is consistent with no variation over a look-back time of ∼11.4 Gyrs.
Name: Davelaar, Jordy
Talk/Poster: Poster
Title: Modeling M81* with a tilted accretion disk
The center of the galaxy M81 harbours a bright radio source, M81*. Martí-Vidal et al. 2013 found that there is a periodic trend visible in the core shift angle, possibly caused by a precessing jet. This type of precessing jet has not yet been fully described by theory.
In this work, I investigate a tilted accretion disk model that is capable of producing a precessing jet. I use a GRMHD code to evolve a tilted-disk accretion flow. From the GRMHD data I compute radio images using radiative transfer codes. These images allow for calculation of the core shift of the source between two observing frequencies. The precessing jet manifests as a periodic core shift angle in the radio images. This model may also be useful in characterising quasi periodic oscillations found in x-ray binaries.
While this model shows promise in explaining the periodicity of M81*, it still has some shortcomings due to the setup of the numerical GRMHD simulation. These issues may have an effect on the observables. I characterise these shortcomings and describe the future efforts to deal with them.
Name: de Bruyn, Ger
Talk/Poster: Talk
Title: Very wide field VLBI in the LOFAR EoR windows
The angular resolution of LOFAR using its (currently) 12 international stations is about 0.3", better than that of ground based optical telescopes. It can create such sharp images over a field of view of at least 5 degrees diameter or more (i.e. 30 Gipapixels) in a single multi-beam synthesis depending only on the 'quality' of the ionosphere. This allows accurate studies of the sub-arcsecond morphology of bright radio sources, polarized radio galaxies and starburst galaxies. I will illustrate this potenatial with some results for the LOFAR EoR 3C196 and NCP windows.
Name: de Vries, Martijn
Talk/Poster: Poster
Title: A deep Chandra view of AGN feedback in the merging cluster Cygnus A
Cygnus A is a famous bright X-ray and radio galaxy, housing a powerful AGN. Its proximity and brightness makes it the perfect target to study the interaction between an AGN and its environment. This interaction has created a wealth of features, such as jets, lobes and hot spots, that are observable in multiple wavelengths. Cygnus A is also undergoing a merger within the larger cluster environment, possibly contributing to the strong AGN activity in the core.

A new, multi-wavelength observation campaign on Cygnus A is ongoing. The campaign includes a 2MS deep exposure with the ACIS instrument on NASA’s Chandra X-ray observatory. We present a preliminary analysis of the first 600ks of this data. The deep exposure combined with the excellent spatial resolution of ACIS allows us to make detailed maps of the temperature and abundance distribution throughout the core. We observe features not previously detected in Cygnus A, such as a cold filamentary structure extending beyond the shockfront, likely to be cold gas from the core dragged outwards by the X-ray cavities expanding through the ICM. We also observe a power law spectrum in the lobes and the jets, indicating Inverse Compton or synchrotron processes.

Looking beyond the core on a larger scale, we have also studied the temperature profile along the merger axis. We see multiple temperature jumps between the core of Cygnus A and the subcluster to the northwest. These temperature jumps are strong evidence of shocks, generated by the infalling motion of the subcluster.
Name: Decleir, Marjorie
Talk/Poster: Poster
Title: The variation of the dust attenuation curve in the nearby Universe
Interstellar dust absorbs and scatters nearly half of the starlight in the Universe, heavily influencing our view on galaxies. Furthermore, it plays a crucial role in several astrophysical processes. A full understanding of the dust properties and the interplay between dust and starlight is essential to recover the stellar light obscured by dust, and to determine the energy balance between gas heating and cooling processes. It is hence fundamental to probe the current and past star formation activity and to constrain the cosmic star formation history.

In extragalactic studies, the dust attenuation law is usually assumed to be similar to the Milky Way for normal galaxies, while the so-called Calzetti relation is used for starbursting galaxies. However, there is growing evidence for strong deviations from a universal dust attenuation law.

We have initiated an ambitious program to study the variation of the dust attenuation curve and the dust properties in the nearby Universe. It is based on the SINGS/KINGFISH sample, a unique local galaxy sample spanning a wide range of morphological galaxy types, metal abundances and star formation activity. We are gathering multi-wavelength imaging data for this sample, covering the UV to the submillimeter wavelength range. Particularly important for our goal are UV data, which we are gathering from the GALEX and SWIFT missions.

In this poster, we will present the first results of our analysis of the variation of the dust attenuation curve on spatially resolved scales of about 200 pc in the spiral galaxy NGC 628.
Name: Dominik, Carsten
Talk/Poster: Talk
Title: Year one of SPHERE disk observations
A bit more than a year ago, SPHERE started observations with open time, and with guaranteed time observations focused on the detection of planets around young stars, and on protoplanetary disks and debris disks. In my talk I will summarize the results of the first year of observations and introduce you a gallery of pictures of disks observed during this time. I will discuss what we have learned,and how these results connect to ALMA data.
Name: Drozdovskaya, Maria
Talk/Poster: Talk
Title: Cometary ices in forming protoplanetary disc midplanes
In my talk I would like to present the results of my PhD research project that I have been carrying out in the group of Prof. Dr. Ewine van Dishoeck for the past 3.5 years on the topic of cometary ices in the midplanes of protoplanetary disks in the embedded phase of star formation. The midplanes harbor the dominating reservoir of icy dust grains that will be used to build protoplanets and comets [Drozdovskaya+ 2014, 2016]. My approach is a combination of a physical model [such as that of Visser+ 2009, 2011; Harsono+ 2013], wavelength-dependent radiative transfer (RADMC-3D) and a large gas-grain chemical network [McElroy+ 2013; Garrod & Herbst 2006; Walsh+ 2014a, b] to study the effects of dynamics and kinetic chemistry on the content of midplanes. It is found that the dominant ice constituent in midplanes is water, however carbon dioxide may dominate in the outer disk for pure infall. Complex organic molecules are most abundant at large (R>30 AU) disk radii and may become as abundant as methanol ice. Dynamic infall is crucial for facilitating complex organic molecule formation thanks to elevated temperatures and additional FUV photons. The results also show that the prestellar fingerprint of volatiles is modified by chemistry during the extra time taken to form the disk. These models set the scene for rigorous comparisons with the chemical content of our Solar System, which is currently being quantified for 67P with the Rosetta mission [Le Roy+ 2015].
Name: Dvornik, Andrej
Talk/Poster: Poster
Title: Detecting assembly bias using galaxy-galaxy lensing with the KiDS and GAMA survey.
We investigate the signatures of galaxy halo assembly bias for spectroscopically selected galaxies from the GAMA survey using weak lensing measurements performed with the spatially overlapping regions (240 square degrees) of the deeper, high imaging quality photometric KiDS survey. We interpret the measured signal armed with a highly flexible halo model. Selecting central galaxies in rich GAMA groups (with richness between 5 and 20), we identify samples with comparable mean host halo masses but with significantly different halo properties, such as the radial distribution of satellite galaxies and the average color of the satellite population. As those are proxies for the formation time of the haloes, we interpret those differences as imprints of assembly bias. To guide our interpretation, we show preliminary comparisons with mock group catalogues and with the predictions from the state-of-the-art hydro-cosmological simulation EAGLE. Our measurements refer to galaxy groups with typical masses of 10^13 Msun/h, naturally complementing the study of Miyatake et al.[1], who reported the first direct detection of assembly bias on galaxy cluster scales (masses ~ 2*10^14 Msun/h). As in their case, our findings undermine the main ansatz behind the standard halo model paradigm, thus reinforcing the message that in the era of precision cosmology assembly bias effects must be included in the modeling of the gravitational lensing signal from galaxies.

[1] Phys. Rev. Lett. 116, 041301 (2016)
Name: Engbersen, Ton
Talk/Poster: Talk
Title: The long shadow of Big Data, Cloud and cognitive computing....
Our ability to create and collect data is rapidly increasing, much more rapid then our ability to process, store and digest it. In particular in some areas of astronomy, new instruments are coming on-line or area already on-line which challenge the traditional way we have been processing this data. But astronomy is no lone ranger here! DNA sequencers and many healthcare solutions keep pace with astronomy. In this forward looking presentation we will argue that the way we work will change significantly. This so-called "Big Data" era can also be seen as a "Big Change" era. IT as we know it will be complemented with cognitive capabilities, because without these we will never be able to reap the benefits of the opportunities ahead. Until now we have used IT to automate the world, from now on we will use IT to understand -and control?- the world. What will be the implications on astronomy? Where do we store our data? Where do we compute on our data? How will IT future IT systems deal with "IoT"? These and many more questions will be visited.

Ton Engbersen has been with the IBM Research Laboratory since 1980. His career spanned such diverse areas as Image processing, chip design, communications technology, server technology, legacy management and Innovation in Outsourcing. Throughout the years he has held a range of management positions in Research and Development in Switzerland and in the US. A member of the IBM Academy of Technology he led the European branch from 2009-2011. Currently he is the Scientific Director for the ASTRON-IBM Center of Exascale Technology, and leading the DOME Project (http://www-03.ibm.com/press/us/en/pressrelease/37361.wss) Since Jan. 2016 he is honorary professor Data Science Engineering at Groningen University. Ton holds an EE Master from Eindhoven University, Netherlands and a PhD from the Swiss Federal Institute of Technology, Zurich.
Name: Fraga-Encinas, Raquel
Talk/Poster: Talk
Title: Probing spacetime around Sagittarius A* using modeled VLBI closure phases
The emission region and black hole shadow of Sagittarius A*, the supermassive black hole at the Galactic Center, can be probed with millimeter Very Long Baseline Interferometry. Our goal is to constrain the geometry of the emitting plasma around Sgr A* by using modeled mm-VLBI closure phase calculations at 1.3 mm. We have simulated images for different models of the emission of Sgr A*: an orbiting spot, a disk model, and a jet model. The orbiting spot model was used as a test case scenario, while the disk and jet models are physically driven scenarios based on standard three-dimensional general relativistic magnetohydrodynamic simulations of hot accretion flows. We present our results, compare them to currently available closure phase observational limits and discuss the implications on the geometry of the plasma.
Name: Götberg, Ylva
Talk/Poster: Talk
Title: Stripped stars emit ionising radiation
Authors: Ylva Götberg, Selma de Mink & José Groh

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 photon 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 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.
Name: Gardenier, David
Talk/Poster: Poster
Title: A model-independent comparison of accreting black hole and neutron star variability
Changes in the emission of X-ray binaries allow a distinction to be made between various spectral energy states. These states are thought to originate from differing physical structures of the accretion flow. While commonly the spectral state is determined by fitting spectra, a variability based technique presented in Heil, Uttley & Klein-Wolt (2015) enables rapid classification of these states. Using ratios of integrated power over equally spaced frequency bands, they show binaries follow distinct paths corresponding to their state. I have extended this method to cover neutron star systems, allowing binary systems with a similar geometry to be compared. I am also looking at the influence of various system parameters on the spectral energy states, and the physical implications of varying spectral state evolution between binary systems.
Name: Guo, Difeng
Talk/Poster: Poster
Title: The Sco-Cen OB association and the Gould Belt
Difeng Guo1, Lex Kaper1, Anthony Brown2, Jos de Bruijne3
1Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands
2Leiden Observatory, The Netherlands
3ESA ESTEC, Noordwijk, The Netherlands

The Gould Belt is a ring-like molecular gas structure hosting newly formed stars, with the Sun located approximately at the center of the ring. All massive OB-type stars visible by naked eye are located in the Gould Belt. The plane of the ring has an inclination angle of about 20 degrees relative to the Galactic plane; the physical origin of the Gould Belt is not known. The Sco-Cen region is one of the embedded OB associations, still actively forming stars in the associated rho Oph molecular cloud complex; membership, stellar kinematics, mass function, age (gradient) and star-formation history are addressed by analyzing parallax, proper motion, radial velocity and extinction of the individual stars. We are re-evaluating the stellar population of the Sco-Cen region based on new and archival data, in preparation for the release of Gaia observations. Our ultimate goal is to reconstruct the star-formation history of the Gould Belt, and to determine its physical origin. Recently we further substantiate the division in subgroups based on kinematical properties of the low- and high-mass stellar population.
Name: Haffert, Sebastiaan
Talk/Poster: Poster
Title: The Leiden EXoplanet Instrument (LEXI): A high-contrast high-dispersion spectrograph
The Leiden EXoplanet Instrument (LEXI) will be the first instrument designed for high contrast high dispersion integral field spectroscopy at optical wavelengths. High contrast imaging (HCI) and high dispersion spectroscopy (HDS) techniques are used to reach contrasts of ~10^-7. LEXI will be a bench-mounted, high dispersion integral field spectrograph that will record spectra on a small area around the star with high spatial resolution and high dynamic range. A prototype is being setup to test the combination of HCI+HDS and its first light is expected in 2016.
Name: Hakim, Kaustubh
Talk/Poster: Talk
Title: High pressure-temperature laboratory experiments to probe the interior of rocky exoplanets
Recent discoveries of small rocky exoplanets in chemically diverse planetary systems suggest that these planets may contain significantly higher amounts of lighter elements, specifically carbon, than the terrestrial planets in our solar system. This poses a challenge for the construction of interior structure models of such exoplanets since those models are often based on the extrapolation of knowledge about the relatively carbon-poor terrestrial planets.

We perform high-pressure, high-temperature laboratory experiments to probe the interior of carbon-poor and carbon-rich rocky exoplanets. We study the physical and chemical properties of minerals and melts that could be present in the mantle and core of these planets. We analyse and quantify the effects of addition of carbon on the interior structure and phase compositions of rocky exoplanets with the help of compositional analyses of our experimental run products.

For our carbon-poor experiments, we find sulfur-poor iron blebs surrounded by sulfur-rich iron melt and olivine crystals surrounded by silicate melt. For our carbon-rich experiments, we find sulfur-rich carbon-poor iron melt, olivine crystals surrounded by silicate melt and carbon in the form of graphite. This suggests that the carbon-rich planets may have interiors made up of thick layers of graphite or diamond.
Name: Halbesma, Timo
Talk/Poster: Poster
Title: Numerical simulations of the merging cluster of galaxies Cygnus A
The Cygnus A galaxy (z = 0.056) hosts an AGN that is a thousand times brighter than any other AGN at the same distance. Moreover, it is located in a cluster of galaxies that is currently undergoing a merger between two sub-clusters. Ultimately we want to understand whether the extreme bright AGN could be triggered by the ongoing merger at a larger scale. In this Master's project we will set up idealised (isolated, binary) galaxy cluster mergers of different mass ratios, initial velocities and impact parameters. We assume the initial conditions for an individual cluster are governed by an ideal gas in hydrostatic equilibrium (a beta model), which resides in a dark matter potential (a Hernquist model). The numerical simulations will be performed within the AMUSE framework using the publicly available cosmological TreeSPH code Gadget-2. We will investigate the contribution of the merger to the total energy budget of the intra cluster medium (ICM) by inferring the shock properties from the radial temperature, density and pressure profiles to obtain where and how much of the kinetic energy is deposited into the ICM. In this poster presentation the latest results of the project will be shown.
Name: Hernandez, Svea
Talk/Poster: Talk
Title: Chemical abundances of extragalactic young massive clusters
The identification of Young Massive Clusters in external galaxies
allow us to take the study of star clusters to extragalactic
distances, beyond the Local Group. Luminous star clusters as massive
as ~10^5 Msun provide high S/N spectra suited for detailed abundance
analysis even at distances of several Mpc. Using the X-Shooter
Spectrograph on VLT and through the interpretation of their
intermediate resolution spectra we estimate abundances of alpha and
Fe-peak elements using stellar atmospheric models.
Name: Hoeijmakers, Jens
Talk/Poster: Talk
Title: Search for reflected light of hot-Jupiter Tau Boo b at high spectral resolution
Only a handful of the exoplanet hosting stars discovered to date are bright enough so that their planets can be studied with realistic amounts of telescope time. Important contributions have come from transit transmission spectroscopy (when the planet passes in front of the star, often using the HST and large ground-based telescopes), and infra-red secondary eclipse measurements in the infra-red (because the planet-to-star contrast is higher at infrared wavelengths, and mainly done using the Spitzer space telescope). Studying exoplanets outside of transit at visible wavelengths, has proven to be a formidable challenge.

Tau Boo b is a non-transiting hot-Jupiter orbiting a bright main-sequence F7 star with a visible magnitude of 4.5. Because the system is so bright, searches for its reflection spectrum at visible wavelengths started immediately after it was discovered in 1997. There have been at least four major searches for light reflected from this hot-Jupiter. This was done using high-resolution echelle spectra, and by searching for the reflected stellar spectrum, that is Doppler shifted to the orbital velocity of the exoplanet upon reflection. The planet was not detected in any of these searches.

We have re-analyzed existing Echelle spectra obtained by the Espadons, Narval and UVES spectrographs, and are able to rule out a planet-to-star contrast ratio greater than 1.5E-5. This is equivalent to a geometric albedo less than 12%, making this hot gas giant darker than the Moon at the 3-sigma confidence level. This albedo is at the low end for what is expected for hot-Jupiters, and means that its atmosphere is likely cloud-free.
Name: Hoekstra, Henk
Talk/Poster: Talk
Title: Results from the KiloDegree Survey
The KiloDegree Survey (KiDS) is an ongoing Dutch-led imaging survey using the VST. Thanks to the combination of excellent image quality and overlap with spectroscopic surveys it is possible to study in great detail the distribution of dark matter in different cosmic enviroments. In this talk I will present several highlights of this project, based on the first half of the data.
Name: Igoshev, Andrei
Talk/Poster: Poster
Title: Natura evanesca/elusive nature: high order multipole structure of magnetic field survives the fall back episode
A.P. Igoshev, J. Elfritz and S. Popov

It has long been thought that small-scale magnetic structures on the neutron star (NS) surface should suffer fast decay during the fallback episode. Our new 2D magneto-thermal simulations suggest the opposite. For the first ~10 yrs after the fall back episode, the observed NS magnetic field appears? dipolar, which is insensitive to the initial magnetic topology. During this interval, non-thermal radiation is strongly suppressed. As the initial (i.e. multipolar ) structure begins to reemerge through the NS crust, this can significantly affect the curvature of the magnetospheric field lines in the emission zone. We distinguish three evolutionary epochs for the re-emergence process: the growth of internal toroidal field, the advection of buried poloidal field, and slow Ohmic diffusion. The efficiency of the first two stages can be enhanced when small-scale magnetic structure is present, and thus pulsed radio emission can be activated if such structure was present in the initial conditions. We have found two candidates, J1107-5907 and J1154-6250, which based on our simulations could be young pulsars currently experiencing magnetic reemergence.
Name: Kamp, Inga
Talk/Poster: Talk
Title: DIANA: Multi-wavelength disk models for the community
In this EU FP7 project, we modeled a well studied sample of protoplanetary disks by combining multi-wavelength continuum and line data taken with space telescopes (HERSCHEL, XMM, HST, SPITZER) and with ground-based observatories (VLT, JCMT, APEX, ALMA, eMERLIN). Large amounts of survey data exist, but are seriously under-utilised. Within DIANA, we collected, analysed and interpreted these data and made it available through a database. Using a homogeneous modeling approach across all objects, we provide best fitting Spectral Energy Distributions and radiation thermo-chemical models to the community. I will summarize here a few applications for these models: (1) revisit diagnostics based on single observational quantities such as CO line fluxes or mm continuum, (2) provide new robust diagnostics, (3) investigate the conditions for planet formation over the disks full radial extent and (4) provide predictions for future observing programs/facilities such as JWST and SPICA.

(on behalf of the DIANA team)
Name: Kaper, Lex
Talk/Poster: Talk
Title: MOSAIC, the multi-object spectrograph for the E-ELT
With its 39m primary mirror, the ESO Extremely Large Telescope (E-ELT) will be the largest optical/near-infrared telescope ever built. MOSAIC is expected to become the E-ELT’s workhorse instrument for astrophysics, intergalactic medium studies and cosmology in the coming decades. MOSAIC will fully explore the large aperture and superb spatial resolution of the biggest eye on the sky. Key science cases involve searching for extra-galactic planets, resolving stellar populations in thousands of nearby galaxies, and studying high-redshift galaxies at the edge of the visible universe. MOSAIC is a fiber-fed spectrograph, covering the telescope’s full field of view with several hundred fibers and a dozen integral field units with adaptive optics capability delivering milli-arcsec spatial resolution, providing spectra ranging from the ultraviolet to the near infrared (380 – 2500 nm) at intermediate spectral resolution. The MOSAIC consortium includes scientists from Brazil, France, Germany, The Netherlands, and the United Kingdom, as main partners. Another 5 European countries are associated with the consortium at different levels.
Name: Keller, Christoph
Talk/Poster: Talk
Title: Exoplanet Characterization with EPICS at the E-ELT
Characterizing exoplanets to answer the question “are we alone?” is a prime science goal for the E-ELT. The ExoPlanets Imaging Camera and Spectrograph (EPICS) will answer questions such as: Are planetary systems like our Solar System common? How frequently do rocky planets settle in habitable zones where liquid water can be present? Do the atmospheres of exoplanets resemble those of the planets in our Solar System? How is pre-biotic material distributed in protoplanetary discs? Is there liquid water on an exoplanet? Are there signs of life on any exoplanets?

EPICS will push the limits of current technologies to achieve the required contrast between the star and the planet of 10-9 and beyond. New optical components and data processing approaches being developed for EPICS already enable the very best exoplanet observations with current telescopes and had a major impact in other fields such as air pollution measurements and biomedical imaging.
Name: Kenworthy, Matthew
Talk/Poster: Talk
Title: The bRing project: Looking for exomoons and rings around the exoplanet beta Pictoris b
The young bright star beta Pictoris has a disk and a gas giant exoplanet in orbit around it, both nearly edge-on to our line of sight. Direct imaging of the exoplanet suggests that the region of gravitational influence of the planet, the Hill sphere, will move in front of the star in 2017, and previous photometric data implies that the planet itself may transit.

We are building the "beta Pic b ring" (bRing) camera in Leiden as part of a campaign to monitor beta Pictoris for the next 18 months and look for circumplanetary material moving in front of the star. The camera will be deployed in South Africa and join other telescopes in providing continuous monitoring of the star. Our simulations suggest that we can detect rings and these can indirectly imply the existence of moons around the planet.

We will present the design and expected performance of the bRing cameras along with initial simulations of ring systems and their resultant photometry.
Name: Klarmann, Lucia
Talk/Poster: Talk
Title: Interferometric evidence for quantum heated particles - tracing carbon in PPDs around Herbig stars
The chemical composition of the inner part of protoplanetary disks is the basis for the atmosphere and bulk composition of rocky planets. Not least because of its biological importance, carbon is one of the key elements to be traced on the path to planet formation.
The PIONIER VLTI Herbig Ae/Be survey provides resolved observations of these inner parts. For some sources, these observations reveal a large amount of extended near-IR flux, more than expected from scattered light. The same sources also show a larger amount flux in the mid-IR polycyclic aromatic hydrocarbon (PAH) features, indicating that quantum heated particles might also contribute to the NIR flux.
Detailed radiative transfer models of HD100453 make it possible to constrain the position, size, amount and scale-height of these quantum heated particles. While adding PAHs does not provide enough near-IR flux, adding 10^{-7} solar masses of very small carbonaceous particles (r=0.006 micron) with a scale-height of 1 AU does. Since these particles have only very weak features, they also lead to a realistic overall spectral energy distribution.
It also means that compared to other solids like silicates, it is very difficult to identify such particles via their features. But interferometric observations in the NIR can not only identify them, but also constrain their size and abundance in the zone of terrestrial planet formation.
Name: Kondratiev, Vlad
Talk/Poster: Talk
Title: Radio spectra of millisecond pulsars
Both physics of the pulsar emission mechanism and free-free absorption in the intervening interstellar medium can be tested with the pulsar radio spectra. Here, we build on our previous work on describing LOFAR population of millisecond pulsars (MSPs, Kondratiev al. 2016, A&A, 585, 128) and HBA census of slow pulsars (Bilous et al. 2016, A&A, accepted, arXiv:1511.01767) and present the study of radio spectra of the MSPs with a special attention on the low-frequency turnover. We present flux density variations in the LOFAR's frequency range 110-188 MHz for more than 40 MSPs in our sample on the time scales of up to three years. Together with published data at other radio frequencies we construct spectra of the MSPs, discuss their broadband spectral behaviour, and compare with the spectra of slow pulsars.
Name: Kooistra, Robin
Talk/Poster: Talk
Title: Going beyond the SDSS cosmic web: HI filamentary emission as a direct probe of large scale structure
The most prominent features in the cosmic web are the large scale filaments, tens of Mpc in size.
However, they have so far only been observed indirectly in large galaxy surveys through the
positions of galaxies. In our work, we instead focus on the observability of the gas in the filaments.
We use high resolution simulations to predict the intensity of HI emission from IGM filaments and
make predictions for the direct detectability of specific filaments previously inferred from SDSS
data. Our study will show that HI emission from large filaments with relatively small inclinations to
the line of sight can be observed by current and next generation radio telescopes.
Name: Korol, Valeriya
Talk/Poster: Talk
Title: A bright future for double white dwarf binaries
Ultra-compact double white dwarf binaries (DWD) represent an interesting systems for a number of reasons.
First, DWDs are binaries that experienced at least two phases of mass transfer, and thus provide a good test for binary evolution theories.
Second, double CO WDs have been proposed as progenitor systems of SN Ia events, used as cosmological distance indicators.
Third, DWDs represent guaranteed sources for the eLISA mission, and will dominate low frequency gravitational wave band from mHz to few Hz.
Finally, detached DWD binaries with orbital periods of 20-40 min represent ideal systems to study the reaction of their internal structure to tidal forces.
This reaction may give us important information on some internal properties of white dwarfs.

I will present an estimation of a sample of ultra-compact detached DWD binaries that could be obtained with Gaia and LSST through EM radiation, and with eLISA in GWs, in two next decades.
I will talk about future synergy between GW and EM data for these sources.
I will show my preliminary results on the role of tidal interaction in the last stages of ultra-compact binaries evolution.
Name: Lopez, Kristhell
Talk/Poster: Poster
Title: NIR counterparts of ULXs
The X-ray luminosities of 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. We have confirmed spectroscopically several M-type
RSG donors. We observed 16 ULXs last April 2015, of which we found 8 candidate counterparts. We will provide an update of our most recent observing campaigns and discuss the impact of our findings.
Name: Lucero, Danielle
Talk/Poster: Talk
Title: Neutral hydrogen in M83 observed with the SKA Pathfinder KAT-7
We present KAT-7 observations of the neutral hydrogen (HI) line and polarized radio continuum emission in the grand design spiral M83. These observations provide a sensitive probe of the outer disk structure and kinematics, revealing a vast and massive neutral gas distribution that appears to be tightly coupled to the interaction of the galaxy with the environment. We present a rotation curve extending out to a radius of 50 kpc, developed using a detailed three-dimensional model of the gas distribution and kinematics. Based on our new HI dataset and comparison with multiwavelength
data from the literature we consider the impact of mergers on the outer disk and draw conclusions about the evolution of M83. We also study the periphery of the HI distribution and reveal a sharp edge to the gaseous disk that is consistent with photoionization from the IGM.
Name: Lyubenova, Mariya
Talk/Poster: Talk
Title: XSL: The X-shooter spectral library
The XSL project aims to build a new, moderate-resolution stellar spectral library for use in stellar population modelling. Once completed, XSL will represent a significant improvement of current empirical stellar spectral libraries in terms of stellar parameters and wavelength coverage. I will review the main characteristics of the library, the data release plans, and will describe how the community will be best able to use XSL.
Name: Mandal, Soumyajit
Talk/Poster: Poster
Title: Lockman Hole and Abell 1914 through the eye of LOFAR
The Low Frequency Array (LOFAR) is a new generation radio telescope operating at low frequencies (10 - 240 MHz). Digital beam-forming techniques make the LOFAR system agile, and allows for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. This makes LOFAR an ideal instrument to perform large area surveys. Along with this, due to its higher resolution & higher sensitivity, it can be a pioneer telescope to look for large-scale diffuse emission generated by the merging galaxy clusters, which are really hard to study due to their steep spectrum nature and complex geometry. The ionosphere is a serious issue of concern for LOFAR data calibration, as its corrupting effects on radio interferometry vary with time and space, and are increasingly worse at low frequencies.

In this poster, I will present our ongoing work on the ~110 hour observation of the "Lockman hole" field, where we aim to make the deepest image ever at 150 MHz. Further, I present the preliminary results of a LOFAR observation of the merging galaxy cluster Abell 1914, in which we will study the (possibly ultra-steep spectrum) radio halo emission at 150 MHz. Finally, I will elaborate on our future plans to develop better ionospheric calibration strategies for LOFAR and future SKA-LOW.
Name: Marchetti, Tommaso
Talk/Poster: Talk
Title: Constraints on the Galactic dark matter halo from hypervelocity stars
A Hypervelocity star (HVS), according to the Hills mechanism, is a star ejected in a
three body interaction between a binary system and the massive black hole in the
center of our Galaxy. These stars, traveling with velocities of the order of thousands of
km/s on almost radial trajectories, are characterized by their galactocentric origin and by
a velocity greater than the escape velocity from the Galaxy. HVSs are a powerful tool to
probe both the binary population and the star formation history in the Galactic Center,
and they also provide essential information on the shape and mass distribution of the
whole Milky Way, all properties on which tight constraints are currently missing.

In this talk I will present the first constraints on the Milky Way dark matter halo mass from HVSs,
focusing on the consequences for the binary population in the Galactic Center.
To do this we’re comparing the current sample of observed HVSs to their velocity distribution as predicted from the Hills mechainsm.
I will discuss the implication of these results on a cosmological point of view.
Finally, having showed the potential of our method, I will highlight how the future data release from the GAIA satellite will be essential to get tighter and more accurate constraints on these quantities.
Name: Maseda, Michael
Talk/Poster: Talk
Title: JWST science is just around the corner
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 in less than a year. We present the current status of the mission, and discuss the schedule for proposal submission and selection, and the relevant policies.
Name: Massari, Davide
Talk/Poster: Talk
Title: Astrometry towards Extremely Large Telescopes: First results from real and simulated data
The Multi-AO Imaging Camera for Deep Observations (MICADO) camera that will be installed at the European-Extremely Large Telescope has the ambitious goal of reaching a relative astrometric accuracy of only 50 microarcsec. To reach this goal, both predicted and real Adaptive Optics astrometric performances need to be carefully tested. In this talk, I address both the issues. The former is investigated by analysing simulated images built with the instrumental PSF of the MICADO Single Conjugate module. On the other hand, the latter issue is addressed by analysing real Adaptive Optics observations taken with the only currently operating MCAO instrument, GeMS at the Gemini-South Telescope.
Name: Mastroserio, Guglielmo
Talk/Poster: Poster
Title: The effects of spectral hardness changes on reverberation lags
Accreting black holes show characteristic reflection features in their X-ray spectrum, including an iron K alpha line, which result from hard X-ray continuum photons illuminating the accretion disk. Measuring the reverberation lag resulting from the difference in path length between direct and reflected emission, and the spectral distortions to the iron line caused by rapid orbital motion and gravitational redshift, provides a powerful tool to probe the innermost regions around the black hole. Previous reverberation studies, both for supermassive and stellar-mass black holes, have largely ignored spectral variability of the continuum. However, this is a potentially important effect, since a hardening of the continuum spectrum causes non-linear changes in the shape of the reflection spectrum as different transitions in the disk are excited and the ionisation balance is changed. We have studied the effect of a pivoting continuum power-law on the reverberation lag spectrum, assuming a simplified lamp post geometry, and developed an analytic description. Since our model accounts self-consistently for both continuum and reverberation lags, it enables fitting of the cross-spectrum (amplitudes and phases) at all frequencies, and thereby to predict the precise spectral variation as a function of luminosity.
Name: Matthee, Jorryt
Talk/Poster: Talk
Title: The mysterious nature of the COSMOS Redshift 7 galaxy: Have we found a primordial object?
I will present recent results from our search for high-redshift (z>5) galaxies through their Lyman-alpha emission line. Thanks to a very wide field approach with ground-based telescopes, we have found a number of surprisingly luminous galaxies that were previously thought to not exist in the early Universe. This already has important implications for re-ionisation and future wide-field surveys such as Euclid. Even more spectacular is the nature of our brightest galaxy, COSMOS REDSHIFT 7 (CR7), which shows spectroscopic evidence for a very hot source (10^5 K) in an extremely low metallicity gas (Z<3x10^-3 Zsun). CR7 has sparked a lot of theoretical investigations into its nature and is thought to consists either of PopIII-like stars or a Direct Collapse Black Hole. I will review the current observational and theoretical constraints and present how we will use HST and ALMA to reveal the nature of CR7.
Name: Mernier, Francois
Talk/Poster: Poster
Title: Chemical enrichment in the hot intra-cluster medium
The hot intra-cluster medium (ICM), permeating the large gravitational potential well of galaxy clusters and groups, is rich in metals, which can be detected via their emission lines in the soft X-ray band. These heavy elements (typically from O to Ni) have been synthesized by Type Ia (SNIa) and core-collapse (SNcc) supernovae within the galaxy members, and continuously enrich the ICM since the cosmic star formation peak (z ~ 2-3). Because the predicted chemical yields of supernovae depend on either their explosion mechanisms (SNIa) or the initial mass and metallicity of their progenitors (SNcc), measuring the abundances in the ICM can help to constrain supernovae models.
In this study, we use XMM-Newton/EPIC to measure the abundances of 9 elements (Mg, Si, S, Ar, Ca, Cr, Mn, Fe and Ni) in a sample of 44 cool-core galaxy clusters, groups and ellipticals (the CHEERS catalog). Combining these results with the O and Ne abundances measured using RGS, we establish an average X/Fe abundance pattern in the ICM, and we determine the best-fit SNIa and SNcc models, as well as the relative fraction of SNIa/SNcc responsible for the enrichment.
Name: Michilli, Daniele
Talk/Poster: Talk
Title: Emission and rotation evolution of pulsar PSR B2217+47
Pulsars are used as precise clocks in different experiments, for example to detect gravitational waves and to test the Theory of Relativity.
Two properties make pulsars such good clocks: a stable rotation, which can be modelled with high accuracy, and a stable emission profile, obtained by averaging star emission over hundreds of rotations.
However, most of the pulsars show fluctuations of different intensities in their rotational periods which are not modelled at present, an effect known as timing noise.
More rarely, changes in the pulse profiles have been observed.
These have the potential to shed light on the internal structure and on the emission mechanism of pulsars, which are still unclear.
Therefore, we conducted a detailed study of the evolution of rotation and of pulse profile for pulsar PSR B2217+47.
The high luminosity, strong timing noise and long baseline make this pulsar a great source for such a study.
We used almost 50 years of data in order to characterize the strong timing noise found in this source.
Our timing residuals show a quasi-periodic modulation over decades.
Furthermore, at LOFAR frequencies we find pulse profile components that appear, evolve and disappear over timescales of months.
In current literature, both effects seem to be related to changes in star's magnetosphere, internal structure and/or orientation.
We are analyzing the relation between these two effects, searching for a common possible explanation.
Our study has the potential to constrain pulsar structure and emission mechanism, as well as to improve pulsar timing models.
Name: Mikhailov, Klim
Talk/Poster: Poster
Title: An Arecibo search for the radio millisecond pulsar nature of the soft X-ray transient 1H 1905+000
Three neutron star binaries are now discovered to undergo transitions between an accretion-powered state *without* radio pulsations and a rotation-powered state *with* radio pulsations: PSRs J1023+0038, J1824-2452I, and J1227-4853. One more binary, 3FGL J1544.6-1125, resembles similar behaviour in optical and X-ray and is thus very likely to transit as well. All four show a relatively low X-ray luminosity (~10^33 ergs/s) in quiescence.

With 300 ks of Chandra data, we have found soft X-ray transient 1H1905+000 to be much dimmer still, less than 2.4 x 10^30 erg/s. This corresponds to the coldest counterpart of the "recycled" radio MSPs. I will review our deep multi-epoch Arecibo observations at 1.4 GHz (2008/2015, due to pulsars steep spectra) and 2.8 GHz (2015, to avoid much scattering along the Galactic plane) in search for radio pulses from the transient.
Name: Molenaar, Gijs
Talk/Poster: Talk
Title: The modern scientists: A contributing software engineer
Practicing modern science is no longer a solitary task; scientists are ever more required to collaborate on larger and larger projects. Data rates in science are exploding, not least in the field of Radio Astronomy. These huge datasets require the aid of software to automate data processing.

The previous two statements require that the modern astronomer is able not only to write software, but also to collaborate in software projects by writing sustainable code. Writing good software is hard and it becomes exponentially harder when the number of developers increases without proper software engineering techniques being used. This talk will be about basic techniques when contributing to, or starting, a scientific software project. The talk will also briefly cover state-of-the-art techniques used to deploy scientific software in a production environment.

Bio: Gijs Molenaar is a software engineer working on data reduction pipelines for MeerKAT (South Africa) and AARTFAAC (Netherlands).
Name: Moravveji, Ehsan
Talk/Poster: Talk
Title: Quantifying the core overshooting and extra mixing with asteroseismology of Kepler B8 stars
Thanks to the high-precision space photometry with Kepler and CoRoT, our knowledge about the internal physical processes in stars is steeply boosting. Specifically with Kepler, we easily reach relative pulsation frequency precision of 1 to 100 parts-per-million. This poses a challenge when modelling the observed frequencies of such stars using our 1D stellar structure, evolution and pulsation theory.

I argue that using our 1D models, we can exploit the rich g-mode frequencies of late B-type stars at a level better than 1%. For two slowly rotating (KIC 10526294) and moderately rotating (KIC 7760680) Kepler B8 stars, the g-modes get efficiently trapped in the overshooting region on top of the receding convective core. This gives us a powerful handle to test the physics of convective overshoot mixing in the radiatively stable interior of massive stars.
Name: Morganti, Raffaella
Talk/Poster: Talk
Title: Massive and fast HI outflows: The case of Mrk231
Massive AGN-driven gas outflows are considered a key component in galaxy evolution. We know now that they have a multi-phase structure and, despite the hostile environment, they include a component of cold gas, atomic (traced by the HI-21 cm) and molecular (traced by CO in the mm). Even more surprising, the cold component appears to be also the most massive one.
I will present a newly discover fast (more than 1000 km/s) HI 21cm outflow in the ultraluminous infrared galaxy Mrk231. Unlike other cases where the radio jet is the main driver, this outflow may be driven by a wide-angle wind and the HI traces the outflow in the very central regions. I will discuss the implications of this result and the future prospects of getting a complete census of these outflows using the surveys planned with Apertif.
Name: Mueller, Cornelia
Talk/Poster: Talk
Title: VLBA+LMT+GBT observations indicate asymmetry in 3mm emission of Sgr A*
Located at the dynamical center of our Galaxy, the black hole candidate Sagittarius A* (Sgr A*) is an ideal target for studying the structure, emission, and dynamics close to an event horizon with high-resolution VLBI. We present the results of our 3mm observations of Sgr A* performed with the VLBA, GBT and LMT on May 23rd, 2015, at unprecedented sensitivity. Imaging and the analysis of closure quantities hint at an asymmetry in the 3mm emission. Comparing with
recent results from VLBI observations at other wavelengths, we discuss this asymmetry in context of possible source intrinsic structure as well as results of interstellar scattering.
Name: Mukherjee, Sampath
Talk/Poster: Talk
Title: Constraining galaxy evolution scenarios from Strong lens simulations with EAGLE
Within the ΛCDM paradigm, dark matter dominates galaxy formation processes. In addition, the complexity of many interacting physical processes such as possible outflows induced by feedback make galaxy formation hard to study. Limited by purely analytic approaches in solving these complex problems we turn to numerical simulations to study some of these open questions. We are addressing these above mentioned and/or similar questions regarding the study of galaxy formation through strong gravitational lensing studies with Evolution and Assembly of GaLaxies and their Environments (EAGLE), a suit of high resolution hydrodynamic simulations. We identify and extract an ensemble of twin lens galaxies and use the GLAMER lensing code to create realistic mock lenses similar to those observed in the SLACS survey. We perform lens-modeling of these mock lenses treating them on equal footing as observed. The comparison between these mock and observed lens galaxies allows us to obtain new constraints on different mechanisms involved in massive early-type galaxy formation. We present the first set of results from our lensing analysis of early-type EAGLE galaxies and discuss different galaxy-formation scenarios on the morphology and configuration of strong lenses thereby providing a statistical framework for constraining galaxy-formation by mock simulations of strong lens systems.
Name: Mulrey, Katharine
Talk/Poster: Talk
Title: Detecting ultra-high energy neutrinos and cosmic rays with the ANITA long-duration balloon
The Antarctic Impulsive Transient Antenna (ANITA) is a long duration balloon-borne observatory designed to detect radio signals from ultra-high energy neutrinos interacting in the Antarctic ice. Ultra-high energy cosmic rays are also seen via geomagnetic radiation produced in the Earth's atmosphere. ANITA uses a 360° array of antennas to scan the ice sheet for radio signals within the 200 -1200 MHz band. The first two ANITA flights set limits on the expected neutrino flux above 10^18 eV and yielded a flux of ultra-high energy cosmic rays. The third ANITA flight took place in the austral summer of 2014-2015 and flew for 23 days. We present the ANITA-III instrument performance and show preliminary data results.
Name: Neijssel, Coenraad
Talk/Poster: Poster
Title: The evolution of the period distribution of massive stellar binaries
Massive stars, at least eight times as massive as our sun, play an important role in astrophysics. Their evolution significantly affects fields such as gravitational waves, enrichment of the interstellar medium and the ionization of the universe. Recent observations show that 90% of the massive stars are in a binary system out of which 70% will interact with their companion. These binary interactions alter the evolution of the stars involved and their predictions for fields in astrophysics. To this day the exact mechanism of binary interactions is not fully understood.
The aim of this research is to study the effects of binary interactions on the orbital period distribution of massive stellar binaries for several observed period distributions of very young regions.
A rapid population synthesis code is used to create and evolve a large sample of massive stellar binaries to see the effects of binarity and the sensitivity to different assumptions.
Results show that the period distribution significantly changes in shape. After millions of years of constant star formation there is an accumulation of systems around an orbital period of 100 days regardless
of the observed initial period distributions. This accumulation is due to mass transfer in binary systems and would naturally explain the period distribution of Be-systems. These results might aid future campaigns for post-interaction products and test the universality of binary interaction mechanism for different clusters.
Name: Nielsen, Ann-Sofie
Talk/Poster: Talk
Title: Long-term spin evolution of X-ray pulsar X1822-371
The LMXB pulsar X1822-371 is a slow x-ray pulsator in an accretion disc corona system, which show properties that are inconsistent with standard theories on how these systems should behave. I will address these inconsistencies. The pulsar is shown to spin up continuously over the 13 years with a spin frequency derivative that gives a spin up timescale of about 7000 years, much shorter than expected for this type of system. The spin up is seen in both long-term evolution, and in shorter timescales of days. This spin up is poorly explained and it is not known whether the system is just showing a spin up with a length of a decade or more, and will then show torque reversal such as, e.g. 4U 1626-67, or if it is really spinning up exceptionally fast. I will talk about this spin up and other aspects of the binary system evolution where it is not clear what the cause is, e.g. the orbital period evolution. The orbital period is expanding on a timescale much smaller than expected. This evolution of the orbital period is not rare for binary systems with a compact star. The theories of why these compact binaries behave like this are as varied as the number of systems showing strange orbital period evolution. I will present a self-consistent scenario where I will try to address all system anomalies with a minimum number of assumptions and show that the current behavior of the system is not reflecting its secular evolution.
Name: Okkuscu, Okan
Talk/Poster: Poster
Title: Mass-flow diagnostics in Herbig Ae/Be stars
HAEBEs are intermediate mass (2-10 M_sun) pre-main-sequence stars contracting to the main sequence and are surrounded by an accretion disk; some are associated with Herbig Haro outflows (jets). Herbig stars, which are the more massive counterparts of classical T Tauri stars (CTTSs) were first identified by George Herbig in 1960 as stars of spectral type A or B with emission lines and which illuminate a bright nebula in their surroundings. Their spectral energy distribution is characterized by an infrared excess due to the dust in the circumstellar environment. We studied the spectral mass loss diagnostics of the following HAEBEs: ESHC1, ESHC7, HD313571/MWC595, HD323771/Hen 3 1425, Hen 3 - 1121N, Hen 3 - 1121S and MWC 953. The optical Hbeta and He I 5876 A lines and the near-infrared He I 10830 A line of these HEABEs are compared with the results of a recent study in a large sample of HAEBEs (Cauley & Johns-Krull 2014, ApJ 797, 112; 2015, arXiv:1506.07546). We extended these diagnostics into the near-infrared spectral range. We also compared HAEBEs with CTTSs to know more details about the physical mechanisms involved in mass accretion and mass outflow.
Name: Oonk, J. B. Raymond
Talk/Poster: Talk
Title: Observing the cold interstellar medium with LOFAR
The interstellar medium (ISM) is the repository of stellar ejecta and the birthsite of new stars and, hence, a key factor in the evolution of galaxies over cosmic time. Cold, atomic clouds are a key component of the ISM, but so far this phase has been difficult to study, because its main tracer, the HI 21 cm line, does not constrain the basic physical information of the gas (e.g., temperature, density) well. New low frequency telescopes open up the opportunity to study this component of the ISM through a complementary tracer in the form of low-frequency carbon radio recombination lines (CRRL). These CRRLs provide a sensitive probe of the physical conditions in cold, diffuse clouds.

In this talk I will focus on three aspects. First of all I will focus on a new suite of low frequency CRRL optical depth models that we have completed this year. These new models differ significantly from previous investigations done in the 1980s. Our new models include the lates rates and cross-sections, a full treatment of the carbon atom, as well as amplification and radiative transfer effects. Secondly, I will show our new LOFAR measurements of CRRLs towards the archetypical CRRL source, Cassiopeia A, and how these in combination with our new models lead to a change in our understanding of the CRRLs at the lowest frequencies. Finally, I will provide an update on our ongoing LOFAR CRRL survey of the Galactic plane and look forward to observing CRRLs with the Square Kilometer Array.
Name: Oostrum, Leon
Talk/Poster: Talk
Title: Millisecond pulsar companions of subdwarf B stars
Subdwarf B (sdB) stars are light (∼0.45 Msun) core helium burning stars near the blue edge of the horizontal branch of the Hertzsprung-Russell Diagram. Recent surveys have shown that a significant fraction is in a short-period binary.

Different formation channels for these systems have been suggested. We focus on the channel predicting a binary with a neutron star (NS) companion. In this case, the system undergoes a phase of common envelope (CE) evolution, causing the orbit to shrink, followed by a short X-ray binary phase. During the latter, the neutron star is recycled. Another CE phase follows, further shrinking the orbit and ejecting the envelope of the secondary. The system then consists of an sdB star and a millisecond pulsar.

We are performing the most sensitive search in the world for these putative radio pulsars. I will present the results of our search and discuss the implications for sdB-MSP systems, providing details on their properties and occurrence rate, which helps constrain binary evolution models.
Name: Ootes, Laura
Talk/Poster: Poster
Title: Neutron star crust cooling in KS 1731-260
Accretion onto the surface of a neutron star in a low mass X-ray binary causes heating of the neutron star crust. Once the system returns to the quiescence state, the crust will cool down. Various theoretical models have been developed that track the thermal evolution of the crust based on energy balance and heat transport equations. By comparison of these models with the observational data the crust parameters can be constrained. However, current models generally assume an (adapted) step function for the accretion rate during the outburst while the light curves of monitoring telescopes show that the outburst profile is in most cases not constant.

I will present our research on the influence of variations in the outburst profile of low mass X-ray binary KS 1731-260 on the predicted cooling curve. This source was in outburst for ~12 years during which it was observed to undergo variations on both long (years) and short timescales (weeks). We modelled the temperature profile of the crust throughout the whole outburst and the subsequent cooling phase using our crust cooling code in which we implemented a module that accurately takes into account the details of the outburst behaviour of the source. Based on the input model we determined how outburst variations on different timescales and in different phases of the outburst influence the predicted cooling curve.

Our results show that variations in the final months of the outburst strongly influence the first ~100 days of the cooling curve. I will discuss the consequences for estimates of the neutron star crust parameters, and I will argue that detailed modelling of the final phase of the outburst is key to constraining the origin of the shallow heat source.
Name: Papastergis, Manolis
Talk/Poster: Talk
Title: The too-big-to-fail problem is too-persistent-to-die: New constraints from nearby field dwarfs
The “too big to fail” (TBTF) problem is a pressing observational challenge to the standard cosmological model at small scales. Put simply, it refers to the fact that it is very challenging to explain both the internal kinematics and the observed number density of dwarfs in the LCDM context. Even though the problem was first identified in the context of the Milky Way satellites, it has now become clear that it concerns dwarf galaxies in general. In this talk, I first plan to give an overview of the observational evidence that supports the statements above. I will then give a brief overview of the most promising solution to the problem, which is a “baryonic” solution within LCDM. I will conclude by showing how present and future observations of HI in nearby field dwarfs can help us distinguish between a cosmological and an astrophysical solution for TBTF.
Name: Peest, Christian
Talk/Poster: Poster
Title: Simulating dust scattering polarization in spiral galaxies
Radiative transfer simulations that describe the propagation of light from and through astronomical objects are gaining more and more importance when interpreting observational data. One observational signature that has not been fully exploited is polarization, which is mainly due to scattering off electrons and dust grains. Recently, this potential is being realized, and a growing number of radiative transfer codes are capable of calculating and predicting polarimetry from astronomical objects.

We have developed an elegant reference-frame-free description of scattering polarization and implemented it into the Monte Carlo radiative transfer code SKIRT. We have validated the accuracy of our implementation using simple test cases and a detailed comparison to other codes. Using our new implementation, we simulate imaging and polarization maps of a realistic spiral galaxy model, with the aim to investigate the possibility to use polarimetry to detect spiral arms in edge-on galaxies. We find that we can easily identify the signatures of spiral structure using polarization information at 1 micron, complementing the information obtainable from regular imaging data.
Name: Petroff, Emily
Talk/Poster: Talk
Title: Fast radio bursts in the era of wide-field interferometers
Fast radio bursts (FRBs) are quickly becoming a subject of intense interest in time-domain astronomy. FRBs have the exciting potential to be used as cosmological probes of both matter and fundamental parameters, but such studies require large populations and currently only 17 FRBs have been published. New telescopes and observing systems in the Netherlands (Apertif/ALERT), Canada (CHIME), and Australia (UTMOST) will detect between 1 and 10 FRBs *per week* when fully operational. More than doubling the population in their first years of operation. I will discuss the developing strategies for maximising real-time science with FRBs from these telescopes and managing the growing population, particularly focusing on the Apertif upgrade to the Westerbork telescope. I will also discuss how our response to these events can inform next generation surveys and pave the way for the enormous number of FRB discoveries expected in the SKA era.
Name: Pietrow, Alexander
Talk/Poster: Poster
Title: IR Background calibration strategies for the E-ELT
METIS is the mid-infrared imager and spectrograph that is currently being developed for the European ELT. Covering the L, M and N bands, it will offer imaging, coronagraphy and spectroscopy. METIS is one of the three first instruments for the European Extremely Large Telescope (E-ELT), and the only instrument to cover wavelengths beyond 3 microns. For this reason and because of the size of the E-ELT, it is necessary to take an in-depth look at the mid-IR background and the data reduction strategies.

We present a first outlook into this matter, based on specialised observations taken with the VLT's VISIR and the GRANTECANs CANARICAM. With steps taken to understand the origins of residuals and quantify them as a function of, amongst other things, angle, throw, frequency and segmentation.
Name: Pleunis, Ziggy
Talk/Poster: Talk
Title: First LOFAR millisecond pulsar discovery
The Fermi telescope has radically changed our view on the gamma-ray sky. However, the inability to identify one-third of its point sources, based on the Fermi data alone, calls for multi-wavelength follow-up surveys. The catalog of unidentified gamma-ray sources acts as a treasure map for finding young and millisecond pulsars (MSPs), as recent surveys have shown. We have performed the first low frequency radio survey towards Fermi sources, which benefits from LOFAR’s sensitivity to ultra-steep spectrum MSPs, along with its excellent field of view for matching the Fermi error regions. The distribution of spectral indices of pulsars is important for understanding the pulsar emission mechanism and the total Galactic population, but surveys for MSPs have been biased towards discoveries at frequencies > 350 MHz. In order to be sensitive to the fastest spinning pulsars, we have used coherent dedispersion in a large-scale search pipeline for the first time. In this survey we have discovered the first MSP with LOFAR (or any digital aperture array) in an observation of Fermi unidentified source 3FGL J1553.1+5437. The discovery of this MSP, PSR J1552+5436, is an important step in probing the full population of MSPs and showing the power that both LOFAR and SKA-low will have for deep MSP surveys.
Name: Ponomareva, Anastasia
Talk/Poster: Talk
Title: The multi-wavelength Tully-Fisher relation: Hunting for the intrinsic scatter
The statistical properties of the Tully-Fisher relation provide important constraints for semi-analytical models and numerical simulations of galaxy formation and evolution. Over the past decades, the scatter in the Tully-Fisher relation has been decreased significantly by accurate photometric measures in the NIR bands. However, the small measurement errors on total luminosity can no longer explain the observed scatter. Therefore, we abandon the classical concept of the Tully-Fisher relation as a correlation using the width of global HI profile and consider instead the internal kinematics of gas in galaxies.
As it is still not clear at which wavelengths the smallest scatter in the relation can be achieved, we assemble the Tully-Fisher relation for a calibrator sample of galaxies with measured TRGB/Cepheid distances over the broad wavelength range from FUV to 22 mm. We implement an improved kinematic measure by deriving high quality rotation curves, taking into account warps and streaming motions in the disk due to spiral arms or a bar.
As a result, our studies show that besides the wavelength dependence, statistical properties of the Tully-Fisher relation are highly sensitive to the internal kinematics of gas. This work is a part of my PhD thesis, which will be complete this autumn.
Name: Por, Emiel
Talk/Poster: Poster
Title: Focal-plane electric field sensing with pupil-plane holograms
For direct detection and spectral characterization of exoplanets, a coronagraph is used to suppress the star light. Amplitude and phase aberrations in the optical train fill the dark zone of the coronagraph with quasi-static speckles, limiting the achievable contrast. Focal plane electric field sensing, such as phase diversity introduced by a deformable mirror (DM), provides a powerful tool for correcting this residual star light. Phase probes applied sequentially on the DM inject star light with a well-known amplitude and phase into the dark zone and the resulting intensity images are combined to estimate the residual electric field. The DM can then be used to add light with the same amplitude but opposite phase to destructively interfere with this residual star light.

Using a static phase-only pupil-plane element we create holographic copies of the point spread function (PSF), each superimposed with a certain pupil-plane phase probe. We therefore obtain all intensity images simultaneously, while still retaining a central, unaltered science PSF. The electric field sensing method only makes use of the holographic copies, allowing for correction of the residual electric field while retaining the central PSF for uninterrupted science data collection. In this paper we discuss the feasibility of this method through numerical simulations.
Name: Posti, Lorenzo
Talk/Poster: Talk
Title: Self-consistent dynamical models for early-type galaxies in the CALIFA Survey
A galaxy’s mass- and stellar velocity-distribution can be determined combining Integral
Field Spectroscopy together with state-of-the-art dynamical models. Here we present
the first application of self-consistent, continuous models with distribution functions (DFs)
depending on the action integrals, to nearby early-type galaxies. We selected two
ellipticals and one lenticular from the CALIFA survey and we fit their surface brightness
distribution and Integral Field-kinematics to our action-based models.
The spatially-resolved kinematics of the CALIFA Survey gives solid constraints
in the models’ parameter space. We reproduce the galaxies’ surface brightness and kinematics,
including line-of-sight velocity and dispersion, out to the CALIFA's spatial coverage (~2-3 Re).
With self-consistent galaxy models we derive dynamical masses, mass-to-light ratios and
orbital anisotropy profiles by fitting a small number of free parameters.
Our results are consistent with those from other popular dynamical models; they are obtained
with much less computational effort than Schwarzschild's and a wider flexibility than Jeans'.
One key advantage of our technique is that we can add multiple galaxy components such as bulge,
stellar disc and dark halo in a self-consistent fashion.
This ultimately enables the reconstruction of the total DF of the galaxy.
Name: Ramsay, Suzanne
Talk/Poster: Talk
Title: The European Extremely Large Telescope
This talk will give a broad introduction to the European Extremely Large Telescope and its Instrumentation. The presentation will cover the design and current status of the telescope as the programme enters an exciting a busy phase. The science case for the telescope will also be discussed. Emphasis will be given to the instruments that are being designed for this new facility.
Name: Redeker, David
Talk/Poster: Talk
Title: The end of the press release as we know it
The press release is dead. Or not? NOVA's press officers David Redeker and Marieke Baan are still sending out some 50 press releases a year to the Dutch media. But the times they are changing. In addition to sending press releases we help media to tell stories, we collaborate with Wikipedia and we make animations for Youtube. Jetlagged from the 'Communicate Astronomy to the Public'-Conference in Colombia we show you the latest tips and trics in this dazzling interactive presentation.
Name: Renzo, Mathieu
Talk/Poster: Talk
Title: Do we understand how stellar winds change stellar fireworks?
Mass loss either by episodic events, such as Roche-lobe overflow, or by steady winds, can have major impact on the final stellar structure and compactness. This can change the final fate (neutron star or black hole), and leave imprints on the resulting supernova lightcurve.

We carry out the first systematic study of mass loss algorithms on the pre-supernova structure and resulting lightcurve. We compute with the Cartesius super-Computer a set of very high resolution stellar models (10-100 times more mesh points than previously published models) with an extensive nuclear reaction network (~200 isotopes), to properly resolve the delayed effect of mass loss on the core structure.

While main sequence winds only remove a small fraction of the total mass, they have a significant effect on the final structure and core mass. Uncertainties in the wind parametrization are responsible a factor of ~2 uncertainty in the final total mass, and they can change the compactness at O depletion by as much as 30%.

We conclude that our current understanding of stellar mass loss constitutes a limiting factor in the study of supernova explosions.
Name: Ribeiro, Evandro
Talk/Poster: Talk
Title: A spectral-timing analysis of the kHz QPOs in 4U 1636-53: The frequency-energy resolved RMS spectrum
Our understanding of quasi-periodic oscillations (QPO) has been further advanced in the last few years by the use of combined spectral and timing techniques, and it is now clear that QPO properties are closely related to the spectral
state of the source in which they appear.

In this work we used all the available RXTE observations of the neutron-star low-mass X-ray binary 4U~1636-53 to study the properties of the kilohertz QPO as a function of energy and frequency.

By following the frequency evolution of the kHz QPOs we created frequency-resolved fractional RMS spectra.
We also studied the connection between the frequency of the kHz QPOs and the parameters of the model that fits the X-ray energy spectrum.

We show the dependence of the QPO properties in a multi-parameter space, and we discuss the implication of our results to the mechanism that produces the QPOs.

Our results provide input to the next generation of
spectral-timing models, which will help us understand the variability and the environment around the neutron star in these systems.
Name: Ribeiro, Nadili
Talk/Poster: Poster
Title: Interstellar magnetic field and dust in the Milky Way
The objective of this work is to improve existing models of the Galactic Magnetic Field, combining radio observations with polarimetric data on the V band. We have a catalogue of roughly 47000 stars with optical polarization measurements for 66 different lines of sight. These lines of sight include 28 open clusters, for which the distances are well known. For the other fields, we cross matched our data with the 2MASS catalogue in order to obtain the magnitudes values for the JKH bands of our stars, through which we are able to estimate the reddening, construct extinction maps, and therefore also make an estimative of distances. All this information will enable us to construct a model of how the dust is distributed throughout the Galaxy, and this model will give us information on the structure of the magnetic field. For this, we are assuming that the elongated dust particles are magnetized, and therefore, have their magnetic momentum aligned with the magnetic field direction, making our polarization measurements a direct measure of the magnetic field direction projected on the plane of the sky. Once this model is ready, it will be used to determine the best 3-D fit of dust distribution and magnetic field of the Galaxy, taking in consideration existing models developed using radio polarimetry.
Name: Ripperda, Bart
Talk/Poster: Poster
Title: Particle acceleration due to tilt and kink instabilities in a low-beta plasma
Magnetic reconnection is the mechanism behind many violent phenomena in the universe.
The energy released during reconnection can lead to non-thermally dominated particle distribution
functions and production of high-energy emission from charged particle acceleration. We
propose a novel route to a regime with multiple, violent reconnection sites in resistive magnetohydrodynamics
(MHD), triggered by a combination of ideal MHD instabilities. A numerical
study of two parallel, adjacent, oppositely directed current channels in an initially force free
equilibrium is presented. The two repelling current channels are liable to an ideal magnetohydrodynamic
stability. This tilt instability has been studied in planar settings, in which it involves
two magnetic islands, which undergo a rotation and a separation on Alfvénic timescales. A
(near) singular current sheet is formed in which particles are accelerated. Using our open-source
grid-adaptive MPI-AMRVAC software, we study the evolution of the tilt instability in twoand-
a-half-dimensional (2.5D) compressible MHD, as well as the evolution of test particles
using the relativistic guiding centre approximation, which we recently implemented. The extension
to full three-dimensional (3D) scenarios is also studied. In this case the tilt evolutions
are affected by out of plane magnetic field components. This makes both current channels liable
to an additional ideal kink instability on top of the tilt disruption, that can trigger tearing
behaviour in the current sheets. In both cases we demonstrate that (up to tearing unstable)
current sheets are formed in the nonlinear regime. The guiding centre approach reveals the role
of drift motions during the nonlinear evolution. We show that reconnection causes non-thermal
particle distributions on Alfvénic timescales in proton-electron plasmas in the low-b regime,
which may have strong implications for particle acceleration in solar flares and other astrophysical
Name: Rivera Sandoval, Liliana
Talk/Poster: Talk
Title: Hunting faint cataclysmic variables in the globular cluster 47 Tucanae
The dense stellar conditions in globular cluster cores dramatically affect the production and evolution of close binary systems. Because of the high interaction rates, these cores are ideal places for studying exotic binary stars such as cataclysmic variables (CVs), which are systems that harbor an accreting white dwarf from a low-mass companion. We have identified the faint CV population of the globular cluster 47 Tucanae by using near-ultraviolet images from the Hubble Space Telescope, in combination with data taken with the Chandra X-ray Observatory. In this work I will show the obtained (and deepest) measurements of the cluster CV luminosity function, and I will compare it to those of other globular clusters, like the core-collapsed globular cluster NGC 6397. I will also compare the number of CVs and their radial distribution with respect to the numbers predicted by evolutionary models.
Name: Saladino Rosas, Martha Irene
Talk/Poster: Poster
Title: AMUSEing winds in binary stars
Most stars are found in binary systems. During their evolution, especially during the AGB phase, stars lose material due to stellar winds; a fraction of this material can be gravitationally accreted by the companion, producing changes in the system. We investigate mass transfer in low-mass binaries to see how the mass accreted by the companion depends on the orbital parameters of the system and how it affects the evolution of the orbit. Using the AMUSE framework, we perform SPH simulations of the outflow from the primary star and by coupling it with a gravity code, we study the interaction of the matter with the secondary. We have studied the flow structure for a few simple cases: a constant wind velocity profile with isothermal and adiabatic equations of state, as well as more realistic simulations in which cooling of the gas has been included. Our preliminary results show a clear spiral structure in the outflow and evidence for an accretion disk forming around the secondary star.
Name: Schoonenberg, Djoeke
Talk/Poster: Poster
Title: Building planets through water condensation
Most models that describe how planets form in protoplanetary disks require an enhanced surface density in solids to form the first generation of planetesimals. However, the mechanism(s) that can lead to such an enhanced surface density in solids are not yet well-understood.

In this study, we investigate the possibility of forming a locally enhanced ‘bump’ in the water ice surface density close to the snowline — the radial distance from the star beyond which water can condense into ice, and within which water ice evaporates into vapour. Due to turbulence, vapour particles diffuse back across the snowline, condensing back onto icy pebbles that are drifting inward. It is precisely this effect that might lead to a local build-up of ice close to the snowline.

Our model takes into account radial drift of solid particles, gas accretion onto the host star, turbulent diffusion, and evaporation and condensation of water ice. We solve a coupled system of time-dependent equations following the surface density of water ice and of water vapour, and the number of solid particles, across the protoplanetary disk.

On this poster we show that under certain conditions, we indeed observe a bump in the surface density of water ice close to the snowline, which might trigger instabilities such as the streaming instability and therefore can lead to the formation of the first planetesimals in a protoplanetary disk.
Name: Schoonhoven, Harm
Talk/Poster: Poster
Title: Lockpicking competition at NAC2016
Lockpicking is the technical sport to open a ordinary lock without keys
and without damaging the lock with a set of specialized tools.
It requires patience and dexterity, but is rewarding in itself if you succeed.
On the poster you can sign up to the competition, sponsored by
Science Café Overvecht (http://www.sciencecafeovervecht.nl).
Place and time of the competition is at the discretion of the LOC.
Introductions to lockpicking can be found at https://www.youtube.com/watch?v=f6ml4USqWXc (in Dutch)
and https://ia801902.us.archive.org/26/items/MITLockGuide/MITLockGuide.pdf .
First price will be the paperback "Surely You're Joking, Mr. Feynman!",
2nd and 3rd price 500g Turkish Delight by Sebahat (Belgium).
The competition is open to all participants of NAC2016.
Name: Schulz, Robert
Talk/Poster: Talk
Title: A radio and X-ray view of the gamma-ray detected radio-loud narrow-line Seyfert 1 galaxy PKS2004-447
The detection of gamma-ray emission in a small sample of radio-loud narrow-line Seyfert 1 galaxies (gNLS1s) has significantly affected the common picture of gamma-ray emitting active galactic nuclei (AGNs) which is dominated by blazars and radio galaxies. Here, we present results from a detailed radio and X-ray study within the framework of the multiwavelength monitoring programme TANAMI. We focus on PKS 2004-447, the only gNLS1 in the southern hemisphere and the radio-loudest one. Consistent with other gNLS1s, it exhibits some properties which are typical for blazars. In contrast to this general picture, the compact-steep spectrum characteristics at radio wavelengths are unique among gNLS1s and very unusual among gamma-ray detected AGNs.
Name: Shariati, Hoda
Talk/Poster: Poster
Title: Global study of flaring stars and flare properties in the Kepler database
Flares are sudden magnetic energy release from the surface of stars which is a proxy of surface magnetic activity. The effects of flares from the central stars on other solar-system planets are important to study regarding the habitability. The stellar flares can potentially ionize the atmosphere of exoplanets, preventing the formation of life or destroying the existing life. In this study, the occurrence of this event on different stellar spectral types is studied to look for any correlation between stellar parameters and flare properties. Aim: By studying a large sample of stars with flaring events and their parameters such as duration, occurrence frequency rate, and amplitude, one can study and establish the correlation between the stellar parameters and flare properties of a significant sample of stars. Method: An automated flare detection algorithm is developed to analyze the long cadence data of Kepler mission. The method removes most long period variability and searches for sharp spikes in the resulting filtered light curves. To parametrize the identified flares, an exponential function is fitted to decay phase. Results: More than 90,000 stars are analyzed and 1800 stars show flaring activity. We do not detect flares in stars with temperatures higher than 10,000 K. Amongst A-type stars, we detect more than 30 candidate flare stars. . Moreover, low mass evolved stars show flares too. The occurrence frequency distribution over all spectral types show a clear exponential decay toward higher numbers.
Name: Shipman, Russell
Talk/Poster: Talk
Title: The HIFI legacy
Since the launch on 14 May 2009, the Herschel 4 year mission had been an enormous success. The operational phase of Herschel completed in Apri1 2013. Since then, the Herschel ground segment has been pouring over all observational results to prepare the data as the legacy of Herschel. This is the Herschel post-operations phase.

One of the three instruments on board, the Heterodyne Instrument for the Far Infrared (HIFI) successfully completed over 9000 science observations of many different types of astronomical sources.

Over the past three years, the HIFI Instrument Control Center (ICC) has endeavored to improve calibration, remove data artifacts, and provide enhanced data products. These HIFI legacy products are available to the entire astronomical community via the Herschel Science Archive.

The HIFI ICC has formally completed its part in post-operations phase of the Herschel mission. I will present an overview of the legacy data that the HIFI ICC has made possible.
Name: Silva, Marta
Talk/Poster: Talk
Title: Unveiling the cosmic web baryons with intensity mapping of IGM filaments
The filamentary large scale structure of the Universe is currently only indirectly probed by galaxy surveys. As a result we have a limited knowledge of the baryonic content and the thermal and ionization state of IGM filaments.
With the help of high resolution simulations we predict the intensity and spatial fluctuation of Ly-alpha and H-alpha emission from IGM filaments illuminated by the UV background. We discuss the prospects for the next generation of UV and optical instruments to detect these signals from the local universe to the epoch of peak star formation activity. By mapping emission from IGM filaments we will be able to directly map the cosmic web and probe the location of the ~30% of the cosmic baryons which have so far been missed by observations.
Name: Smits, Roy
Talk/Poster: Poster
Title: ARTS: An advanced radio transient system at the WSRT
The Westerbork Synthesis Radio Telescope (WSRT) is an array of 14 25-meter dishes spread over an East-West baseline of 2.7 kilometres. For the past 46 years it has been one of the most powerful radio telescopes, allowing astronomers to study a diverse range of astrophysical phenomena. A new upgrade of the receivers will allow the telescope to continue its outstanding performance.

The new receivers, called Apertif (APERture Tile In Focus), will extend the instantaneous field of view of the WSRT by a factor of 37. This will make the WSRT a powerful survey instrument. The wide field of view makes the telescope also sensitive to detecting rare radio bursts, such as RRATS (Rotating RAdio Transients) and FRBs (Fast Radio Bursts).

To allow for a deep search of pulsars and to optimize the detection of radio bursts, an advanced backend called ARTS (Apertif Radio Transient System) is being designed to handle the high data-rates and allow for different modes of observation, including real-time dedispersion.

ARTS will become operational later this year.
Name: Snik, Frans
Talk/Poster: Talk
Title: Liquid-crystal technology for high-contrast imaging with the E-ELT
The vector-APP coronagraph enables direct imaging of exoplanets by manipulating the PSF of a star, such that dark holes appear in the stellar halo right next to the PSF core. This coronagraphic functionality is accomplished with a phase pattern in the reimaged pupil-plane of the telescope. We apply patterned liquid-crystal technology to produce PSFs with extremely dark holes over very broad wavelength ranges. Currently, we attain an unprecedented on-sky contrast of ~1E-5 at 2.5 lambda/D in K-L-M bands. Supported by an ERC Starting Grant, we will enhance the performance of the vector-APP coronagraph, integrate it with other optical modalities like polarimetry, wavefront-sensing, and spectroscopy, and commission vector-APP coronagraphs at several large telescopes for direct exoplanet observations. We are developing high-contrast imaging capabilities based on the vector-APP coronagraph for the E-ELT instruments MICADO, METIS, and EPICS.
Name: Spingola, Cristiana
Talk/Poster: Talk
Title: A panchromatic study of the gravitational lens MG J0751+2716 at z=3.2
The interplay between AGN and their host galaxies, and how strong is the connection between the jets and star-forming episodes or the evolution of the AGN and the host galaxy is not well understood. I will present a detailed multi-band study of MG J0751+2716, a gravitationally lensed radio-loud active galaxy at the cosmological interesting epoch of redshift 3.2. This object consists of extended gravitational arcs, which are clearly detected in high-resolution optical, near-infrared, mm and radio wavelengths at mas-scales. By carrying out a sophisticated reconstruction of the background source using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source-plane for the first time, that includes the heated dust, the molecular gas (CO), the stellar population of the AGN host galaxy and the radio core and jets. The overall mm-to-radio SED is consisted with a significant dust bump associated with ongoing dust obscured star-formation. The object is found to consist of two distinct optical components, separated by a projected distance of 1.5 kpc, that differ strongly in colour. The reddest component is found to be extremely compact, while the blue star-forming object is more diffuse and shows multiple brightness components. The molecular gas distribution, as measured with the CO (1-0) emission is extended over the whole system. The radio-jets, which also extend over ~2 kpc do not appear to be interacting with the blue star-forming component. Further observations at high angular resolution at mm-wavelengths will determine the star-formation conditions within the system.
Name: Stevens, Abigail
Talk/Poster: Talk
Title: Comparing phase-resolved spectroscopy results from QPOs in low-mass X-ray binaries
X-ray spectral-timing is a burgeoning field that seeks to investigate how matter behaves in strong gravitational fields. Observations suggest that different types of quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g. disklike or jetlike) in the innermost part of the X-ray binary, close to the neutron star or black hole. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to a variety of low-frequency QPOs from low-mass X-ray binaries containing black holes or neutron stars. On the QPO time-scale, we find that the energy spectrum changes not only in normalization, but also in spectral shape. In analyzing a variety of signals we will quantify how the spectral shape changes as a function of QPO phase and look for systematic trends between different classes of sources. We can then use these trends to infer the origin of the QPOs and its relation to emitting-region geometry in the strong gravity regime.
Name: Storm, Emma
Talk/Poster: Talk
Title: Shocks in galaxy cluster outskirts: The case of A3667
The outskirt regions of galaxy clusters are rich environments to study structure formation and merger dynamics. The observation of diffuse radio emission in the form of radio relics indicates the existence of cosmic rays that are likely accelerated by shocks in these regions. X-ray observations of cluster outskirts have revealed such shocks, often spatially coincident with radio relics. The merging cluster A3667 hosts a double radio relic, and X-ray observations of the northern region of the cluster previously showed an X-ray shock associated with the northern relic. We use new XMM observations of the southern outskirt of the cluster to investigate the nature of the southern component of the radio relic and a potential second shock.
Name: Straal, Samayra
Talk/Poster: Talk
Title: Unravelling the nature of HESS J1943+213
HESS J1943+213 is an unidentified TeV source, close to the Galactic plane, whose properties are compatible with both a pulsar wind nebula (PWN) and a high-frequency-peaked BL Lac object nature. Some of its unusual observed characteristics are consistent with each of these enormously different astrophysical interpretations. In order to finally classify and understand this object we took a three-pronged approach: time-domain, high angular resolution, and multi-frequency radio studies.

In this talk I will present our paper on HESS J1943+213 (Straal et al., 2016). Our deep time-domain observations with the Arecibo telescope were unable to uncover the hypothesized pulsar powering the proposed PWN. We conclude with ∼70% confidence that HESS J1943+213 does not host a pulsar. In addition, radio observations sensitive to different angular scales reveal a two-component structure: a compact core and an extended structure. Both structures follow power laws. I will discuss why for HESS J1943+213 this is not compatible with a combined supernova remnant - PWN scenario and how this can be used to identify other unresolved HESS sources near the Galactic plane. Overall, we rule out the PWN hypothesis and conclude the source is a BL Lac object.
Name: Szary, Andrzej
Talk/Poster: Talk
Title: On the origin of bi-drifting subpulse phenomena in pulsars
The unusual drift feature was reported within four pulse components of PSR J0815+09, where the drift direction of the second component is opposite to the direction of the two trailing components.The two-direction drift is a great challenge to the pulsar theory.

We present a model which not only explains the observed bi-drifting subpulse phenomenon, but also breaks with the non-physical assumptions of the carousel model. The drift takes place in regions where the charge density is below the so-called co-rotational density, and as such is connected with movement around the rotation axis. We show that incorporating small-scale surface magnetic anomalies results in a change of location of the actual polar cap. The change of position of the polar cap with respect to the rotation axis can lead to the two-direction drift of subpulses.
Name: Talens, Geert Jan
Talk/Poster: Talk
Title: First results from MASCARA: Finding transiting exoplanets around bright (V<8) stars
The Multi-site All-Sky CAmeRA (MASCARA) is a new transit survey that will use two fully automated stations to search for transiting exoplanets around the brightest stars at 4 < V < 8. Planets transiting these bright stars are ideal candidates for follow-up studies of planetary atmospheres, however, current transit surveys are aimed at fainter stars. MASCARA aims to fill this gap and find new exoplanets suitable for atmospheric characterization studies.
The first MASCARA station has been operating on La Palma since late 2014; the second station, located in La Silla, is expected to start observing in Fall 2016. Each MASCARA station is equipped with 5 cameras which provide continuous observations at 6.4 second cadence and full coverage of all bright stars down to airmass 2. Aperture photometry is performed on-site and the resulting light curves are transferred to Leiden observatory for post-processing and transit detection.
To date, MASCARA has collected more than 200 Terabytes of raw data, producing light curves for over 50,000 stars. In this talk I will describe the MASCARA post-processing and transit detection algorithms, and present results from the first year of MASCARA operations.
Name: Torres, Santiago
Talk/Poster: Poster
Title: Dynamics of the Oort Cloud in the Gaia Era
Jan Hendrik Oort proposed in 1950 the existence of the cometary cloud that surrounds the Solar System, but its creation and evolution still remains a mystery today. Studies suggest that comets in the Oort cloud evolve dynamically under the influence of internal (giant planets) and external (random stellar passages and the influence of the galactic tide) disturbers. The aim of this work is to do a detailed study of the cloud’s external perturbation by simulating the Oort cloud in the galactic environment, including the effect of galactic tides and stellar encounters. Simultaneously, we aim to develop a realistic Oort cloud (to the extent possible). For this purpose we will use the Astrophysical Multi-purpose Software Environment (AMUSE) to combine the simulations of the Oort cloud with the effects of galactic tides and stellar encounters. Likewise, we will employ a model of the galaxy, in particular the non-axisymmetric components using the PERLAS code developed by Pichardo et al. (2003, 2004). Using the data, provided by the Gaia satellite, of the stars in the immediate solar neighborhood with high precision in phase space coordinate, we will compute the positions and velocities of the nearby stars, in order to determinate the distance and time (past or future) of their closest approach to the Solar System and its implications on the dynamics of the Oort cloud. We will present our first preliminary results of the effect of stellar encounters in the Oort cloud using the Hipparcos catalogue.
Name: Trager, Scott
Talk/Poster: Talk
Title: WEAVE: Status and surveys
I will discuss the status and survey plans for WEAVE, the next-generation wide-field spectroscopic survey facility for the WHT. WEAVE will provide the necessary spectroscopy to fully exploit the Gaia, LOFAR, and APERTIF surveys. I will particularly highlight the Dutch contributions to the spectrograph and IFU systems and leadership roles in the surveys.
Name: van den Eijnden, Jakob
Talk/Poster: Poster
Title: Differential precession in accretion flows onto stellar-mass black holes
Accreting stellar-mass black holes display quasi-periodic oscillations (QPOs) in their X-ray flux with a period that drifts from 0.05 to 10 seconds. Since this oscillatory signal originates from the close proximity of the black hole, these QPOs provide a powerful probe of the accretion flow in this region of extreme gravitational curvature. Although the exact origin of the QPO is still a subject of debate, the oscillation is expected to show the same frequency in all energy bands. However, the QPO frequency has unexpectedly been observed to depend on photon energy for several accreting black holes. Here I present a model-independent analysis of this energy dependence of the QPO frequency in archival RXTE observations. Using a novel spectral-timing approach, we show that the observed energy dependence is intrinsic to the underlying QPO mechanism. We find that this corresponds to a systematic increase in phase difference between lightcurves in different energy bands during so-called coherence timescales, where the oscillation repeatedly rises and falls in amplitude. We interpret this result within the model of general-relativistic Lense-Thirring precession of the inner accretion flow. As photons of different energies are expected to originate from different radii, our results indicate the presence of differential precession: different radii precess at different frequencies, possibly leading to the gradual decoherence of the QPO. Furthermore, the absence of energy-dependent QPO frequencies in other black hole binaries could shed light on the emission processes of the inner accretion flow.
Name: van der Helm, Edwin
Talk/Poster: Poster
Title: Creating Arches
The Arches cluster is a Young Massive Cluster near the center of the Galaxy. We use AMUSE to simulate the stellar and gas dynamics, stellar evolution and wind inside the galactic gravitational potential to investigate the origin of this cluster.
Name: van der Hulst, Thijs
Talk/Poster: Talk
Title: The WSRT Coma HI survey
An area of three square degrees in the Coma cluster was observed in the 21cm HI line with the WSRT. This is the deepest blind survey in HI of Coma to date and covers the cluster core and the region to the south-east along the large scale structure filament connecting Coma and Abell 1367. The HI mass detection limit is ~10^8 Msun. The observations delivered 47 detections, of which 25 are new. A first inventory of properties and HI morphologies in relation to the local environment will be presented.
Name: van Doesburgh, Marieke
Talk/Poster: Talk
Title: Lense-Thirring precession around neutron stars with known spin
Quasi periodic oscillations (QPOs) are observed in neutron star (NS) low mass X-ray binaries (LMXBs) at high (200-1200 Hz) and low (<100 Hz) frequency.
The relativistic precession model of Stella and Vietri (1998) explains QPOs of a few tens of Hz by the nodal precession of orbits at the inner disk edge due to frame dragging at precession frequency v_LT, identical to the Lense-Thirring precession of a test particle orbit. A quadratic relation between ?_LT and the Keplerian orbital frequency (identified with the observed high frequency QPOs), and a linear dependence on spin frequency are predicted.
In early work (van Straaten et al., 2003) this quadratic relation was confirmed in three objects of uncertain spin.
We compare predictions of the relativistic precession model to properties of QPOs measured in a sample of 14 LMXBs for which the NS spin frequency is now known.
We find we can distinguish two oscillations that occur simultaneously in the predicted precession frequency range. In previous works, these oscillations
have often been confused. For both frequencies, we find correlations with inferred Keplerian orbital frequencies characterized by power laws with indices that differ significantly from the prediction of 2.0.
Also, the required specific moment of inertia of the NS exceeds values predicted for realistic equations of state. We find
no evidence that the NS spin frequency affects the QPO frequencies. We discuss
the possibility that precession of a hot inner flow can happen at frequencies different from
test particle values and consistent with those observed.
Name: Van Eck, Cameron
Talk/Poster: Talk
Title: Faraday tomography with LOFAR
The new generation of low-frequency radio telescopes, including the Low Frequency Array (LOFAR), have opened up a whole new range of observing capabilities and scientific possibilities. These capabilities include high-resolution Faraday tomography (the decomposition of polarized emission by the degree of Faraday rotation), which allows us to probe magnetic fields in our Galaxy. The unique properties of low-frequency polarization give us a new method to probe the local interstellar medium and its magnetic field.

In my talk, I will show my results from applying Faraday tomography to LOFAR observations and demonstrate what this can tell us about the structure of magnetic fields in the local interstellar medium.
Name: van Haarlem, Michiel
Talk/Poster: Talk
Title: Latest news from the Square Kilometer Array
The Square Kilometre Array (SKA) is a large, distributed and highly innovative radio-telescope that will allow astronomers to probe the early phases of the Universe, and to gain a deeper understanding of the fundamental laws of physics. It will be the most powerful radio telescope operating at cm-m wavelengths. The Netherlands is one of the initiators of the SKA and has been leading R&D in aperture array technology, where many small antennas and smart computers replace large traditional dishes. The project will be realised in phases. The first phase, SKA1, is in the detailed design stage with construction due to start in 2018-2019. The SKA Science case is broad and contains a number of key projects in which radio astronomy can make a unique contribution to our understanding of the Universe.

SKA1_low in Australia will consist of nearly 130,000 antennas, distributed over ~500 stations. The operating frequency will be between 50 MHz and 350 MHz. SKA1_mid will be located in South Africa and consist of 200 dishes (including the 64 dishes of the MeerKAT Precursor which will be incorporated). An initial suite of three receivers will cover the 350 MHz - 14 GHz range of the spectrum. Signals from the telescopes and stations will be transported to a central processing facility on-site in each country. Further processing by science teams will take place in a federated and globally distributed network of Science Data Centres (SDC) capable of handling the big data streams coming from SKA.
Name: van Rest, Daan
Talk/Poster: Poster
Title: VLT/X-shooter observations of GRB 160203A in rapid response mode
Gamma-ray bursts (GRBs) are the brightest cosmic explosions, caused by the collapse of a massive star or the merger of a compact binary. Their optical afterglows fade very rapidly, but provide the opportunity to measure the redshift of the GRB and the properties of its host galaxy. For the first time, we managed to obtain an optical to near-infrared spectrum of a GRB afterglow with X-shooter on the ESO Very Large Telescope in rapid response mode, just 18 minutes after the detection of GRB 160203A (T90 = 20.2 sec) with the Swift satellite. The X-shooter spectrum includes a damped Lyman alpha line and various metal absorption lines at a common redshift of 3.52, corresponding to a look-back time of 11.9 Gyr. We report on the derived properties of the GRB host galaxy and the detection of intervening systems.
Name: Vandenbroucke, Bert
Talk/Poster: Poster
Title: A solution for Too Big To Fail
In the quest to falsify the LambdaCDM model of cosmology on small scales, Boylan-Kolchin et al. (2011) identified the so called Too Big To Fail (TBTF) problem when comparing the properties of Local Group dwarf galaxies with the properties of subhalos in a simulated Local Group analogue. Simply put, TBTF refers to the fact that observed dwarf galaxy kinematics point to dwarf galaxies being hosted by low-mass subhalos, while the abundance of dwarf galaxy satellites matches that of more massive subhalos.
As Papastergis & Shankar (2015) show, this issue can be resolved if the observed kinematics of dwarf galaxies somehow mismatches the underlying gravitational potential, i.e. if neutral gas rotation discs do not trace the maximal circular velocity of the halo.
In a large suite of isolated dwarf galaxy simulations (Vandenbroucke et al., 2016), we found a relation between the maximal circular velocity of a dwarf galaxy halo and the rotation velocity of its neutral gas that resembles the Papastergis & Shankar relation remarkably well. We hence argue that TBTF is caused by a mismatch in the way observations and simulations are compared and does not necessarily point to a fundamental problem with LambdaCDM on small scales.
Name: Vats, Smriti
Talk/Poster: Talk
Title: A Chandra X-ray census of the interacting binaries in old open clusters
We are carrying out an X-ray survey of old open clusters with the Chandra X-ray Observatory. Single old stars, being slow rotators, emit very faint X-rays (Lx < 1×10^27 erg s-1). Hence, X-rays produced by mass transfer in Cataclysmic Variables (CVs), or by rapid rotation of the stars in tidally-locked, detached binaries (Active Binaries-ABs), can be detected, without contamination from single stars. By comparing the properties of various types of interacting binaries in different environments (the Galactic field, old open clusters, globular clusters) we aim to study binary evolution and how it may be affected by dynamical encounters with other cluster stars. Stellar clusters are good targets to study binaries as age, distance, chemical composition, etc., are well constrained. I will present our results for two open clusters, Collinder 261 and NGC 188, detailing their low-luminosity X-ray population, in conjugation with other old open clusters (M67, NGC 6791), and in comparison with populations in globular clusters.
Name: Vazan, Allona
Talk/Poster: Talk
Title: Metallicity and the mass-radius relation of exoplanets
For many of the detected exoplanets measurements of both mass and radius are available. The relation between the mass and radius provides information about the metallicity of the planet. However, the radius-mass relation and its time dependency are affected substantially by the thermal evolution of the planet. Often giant planets are modeled under the assumption that they are adiabatic, convective and homogeneously mixed, but this assumption is made mainly for simplicity, and may not be the case. We simulated planetary evolution and focused on various influences of composition on the heat and material transports. We show that planetary evolution depends on initial composition and its distribution, discuss whether the internal structure changes with time, and how it affects evolution and the observed parameters. This study emphasizes the importance of coupling planet formation, evolution, and internal structure self consistently.
Name: Veljanoski, Jovan
Talk/Poster: Talk
Title: The kniematics of globular clusters systems in the outer halos of the aquarius simulations
Stellar halos and globular cluster (GC) systems contain valuable information regarding the assembly history of their host galaxies. Motivated by the detection of a significant rotation signal in the outer halo GC system of M31, in this contribution we investigate the likelihood of detecting such a rotation signal in projection, using cosmological simulations. To this end we select subsets of taggedparticles in the halos of the Aquarius simulations to represent mock GC systems, and analyse their kinematics. We find that GC systems can exhibit a non-negligible rotation signal provided the associated stellar halo also has a net angular momentum. The ability to detect this rotation signal is highly dependent on the viewing perspective, and the probability to see a signal larger than that measured in M31 ranges from 10% to 90% for the different halos in the Aquarius suite. High values are found from a perspective such that the projected angular momentum of the GC system is within
Name: Verbeke, Robbert
Talk/Poster: Talk
Title: Dwarf galaxy simulations with Pop III feedback, and how to “observe” them
Dwarf galaxies occupy the faint end of the galaxy mass function and their properties are often regarded as strong tests for cosmological and galaxy evolution models. Indeed, their shallow gravitational potential makes them very susceptible to both external and internal processes. Using computer simulations, the effects of such processes can be tested (e.g. Mayer et al. 2006, Governato et al. 2010). To do this, the properties of the simulated galaxies need to be closely compared to a broad range of observed galaxy properties and scaling relations.

We present the results of N-body/SPH simulations including radiative cooling, star formation, chemical enrichment, stellar feedback, heating by the cosmic UV background, and feedback from Population III stars (Verbeke et al. 2015) and show that these compare very well to observed galaxies over the entire dwarf galaxy regime, unlike simulations without Population III feedback. We therefore conclude that Population III stars played a crucial role in the evolution of (dwarf) galaxies.

Furthermore, we stress the importance of the way simulations are analyzed. The more in line these mock observations are with real observational techniques, the more reliable the comparison. Obtaining for example the rotational velocity from HI kinematics, metallicities from RGB stars (Kirby et al. 2013), and star formation histories from colour-magnitude diagrams (Monelli et al. 2008) are thus very important and can greatly affect the interpretation of the simulations.

Lastly, we use the insights obtained from our simulations to discuss how the scatter in observed scaling relations can be explained.
Name: Verdoes Kleijn, Gijs
Talk/Poster: Talk
Title: Quasar hosts and early growth of supermassive black holes in the epoch of reionisation
Luminous quasars at high redshift are powered by supermassive black holes. These massive black holes are thought to be located in the progenitors of the massive galaxies we see in the local Universe. We present the results from the sample of QSOs at 5.7
Name: Verheijen, Marc
Talk/Poster: Talk
Title: Science with Apertif - a wide-field 21cm survey camera for Westerbork
Taking advantage of innovative phased-array technology, the new Apertif wide-field radio 'camera' currently being installed on the Westerbork radio telescope, will be used in a 4-year observing campaign starting in 2017 to carry out a shallow imaging survey of ~3000 deg^2, a medium-deep imaging survey of ~300 deg^2, and a transients survey, searching for pulsars and Fast Radio Bursts. It will map the atomic hydrogen gas in a hundred thousand galaxies, produce confusion-limited radio continuum maps, measure magnetic fields in external galaxies and produce a high-density Rotation Measure grid for the Milky Way. In this presentation I will discuss the main scientific questions we intend to answer with Apertif, describe the Apertif Survey Plan and, hopefully, present some first commissioning results.
Name: Verstocken, Sam
Talk/Poster: Poster
Title: High-resolution, 3D radiative transfer modeling of nearby DustPedia galaxies
The DustPedia project aims at conducting a definitive study of interstellar dust in the Local Universe, by gathering multi-wavelength imaging data of nearby galaxies, and modelling them with state-of-the-art modeling tools. As part of the DustPedia project, we create 3D models for a representative set of nearby galaxies using the radiative transfer code SKIRT. We simultaneously derive the 3D distribution and spectral properties of the stellar populations and the interstellar dust in each galaxy, by fitting radiative transfer models directly to imaging data from UV to submm wavelengths. We fully take into account the effects of absorption, multiple scattering and thermal re-emission by the dust in our models.

We present preliminary modeling results on two well-known face-on spiral galaxies, M51 and M81, and focus on the dust heating mechanisms in these galaxies. By using radiative transfer, we take into account the effects of non-local heating, as opposed to for example pixel-by-pixel modeling techniques. We exploit our knowledge of the internal radiation field to investigate the contribution of the evolved and young stellar populations to the heating of the dust at every position in the galaxy. Our results indicate that young stellar populations are not always the dominant heating agent, and that the contribution of evolved population is important as well.
Name: Visser, Rico
Talk/Poster: Poster
Title: On the growth of pebble-accreting planetesimals
Pebble accretion is a new mechanism to quickly grow the cores of
planets. For large bodies, gravity and gas drag ensures large
collisional cross sections --on the order of the Hill sphere-- for
pebble-size particles in protoplanetary disks. However, aerodynamic
deflection may prevent planetesimals from becoming large, because
small particles tend to follow gas streamlines avoiding accretion.
The growth rate is therefore a competition between the (attractive)
gravity of the planetesimal and the (repulsive) drag force of the
gas. The question arises: do pebbles follow the gas around the
planetesimal or will the planetesimal gravity be strong enough to
accrete them?

We derive the planetesimal radius where pebble accretion starts and
determine the growth timescales of planetesimals by sweep-up of small
particles. Smaller pebbles (dust grains) coupled strongly to the gas
and, consequently, the collisional probability is low. For larger
pebbles gravity dominates and rapid growth of the planetesimal
follows. This is the stage in which planetary cores can form quickly,
making it a viable planet formation model. I will talk about the
conditions and time needed to initiate pebble accretion at 1, 3 and
10 AU orbital radius from the star and most importantly: will it be enough to grow a protoplanetary core?
Name: Wang, Lingyu
Talk/Poster: Talk
Title: A critical look at the most commonly used SFR indicators
Measurement of star-formation rate (SFR) is of crucial importance to our understanding of how galaxies build up their stellar content over cosmic time. Observationally, one can use many empirical SFR indicators relying on simple conversion from luminosity in practically every accessible waveband. Therefore inter-comparing these SFR indicators is extremely important if we were to have a reliable, robust and coherent picture of the cosmic star-formation history. Recently, we take advantage of the GAMA spectroscopic survey and the associated large multi-wavelength data to address this issue. We focus on three most commonly used SFR indicators, UV continuum luminosity corrected for dust attenuation using the observed UV colour (or spectral shape), Halpha recombination line luminosity corrected for dust using the observed Balmer decrement ratio, and the combination of the escaped SF traced by the observed UV luminosity and the dust reprocessed SF traced by the IR luminosity. We construct a galaxy sample with very high quality measurements to minimise random statistical errors. Our galaxy sample size is several times larger than previous samples in similar studies. In addition, our sample also covers more distant and less luminous (more quiescently star-forming) galaxies. We carefully analyse the influence of a number of important systematic effects on the SFR indicators. Moreover, we find that the popular dust attenuation correction in the UV highlighted in the recent review paper (Kennicutt & Evans 2012) is not suitable for our sample. We derive a new dust correction in the UV based on calibrating to the total IR to UV and the attenuation in the Halpha line. The three SFR indicators are successfully brought into reconciliation after incorporating the new dust correction and including a number of systematic effect which influences the derived IR luminosity and Halpha line luminosity.
Name: Wang, Yanan
Talk/Poster: Talk
Title: The XMM-Newton spectra of the 2012 outburst of the black-hole candidate 4U 1630􀀀47 revisited
Recent XMM-Newton observations of the black-hole candidate 4U 1630-􀀀47 during the 2012 outburst revealed three relativistically Doppler-shifted emission lines that were interpreted as arising from baryonic matter in the jet of this source. Here we reanalyse those data and find an alternative model that, with less free parameters than the model with Doppler-shifted emission lines, fits the data well. In our model we allow the abundance of S and Fe in the
interstellar material along the line of sight to the source to be non solar. Among other things, this significantly impacts the emission predicted by the model at around 7.1 keV, where the edge of neutral Fe appears, and renders the lines unnecessary. The fits to all the 2012 XMMNewton observations of this source require a moderately broad emission line at around 7 keV plus several absorption lines and edges due to highly ionised Fe and Ni, which reveal the
presence of a highly-ionised absorber close to the source. Finally, our model also fits well the observations in which the lines were detected when we apply the most recent calibration files, whereas the model with the three Doppler-shifted emission lines does not.
Name: Watts, Anna
Talk/Poster: Talk
Title: Thermonuclear burst oscillations - where flames meet fundamental physics
Neutron stars offer a unique environment in which to develop and test theories of the strong force. Densities in neutron star cores can reach up to ten times the density of a normal atomic nucleus, and the stabilising effect of gravitational confinement permits long-timescale weak interactions. This generates matter that is neutron-rich, and opens up the possibility of stable states of strange matter, something that can only exist in neutron stars. Strong force physics is encoded in the Equation of State (EOS), the pressure-density relation, which links to macroscopic observables such as mass M and radius R via the stellar structure equations. By measuring and inverting the M-R relation we can recover the EOS and diagnose the underlying dense matter physics.

One very promising technique for simultaneous measurement of M and R exploits hotspots (burst oscillations) that form on the neutron star surface when material accreted from a companion star undergoes a thermonuclear explosion (a Type I X-ray burst). As the star rotates, the hotspot gives rise to a pulsation. Relativistic effects then encode information about M and R into the pulse profile. However the mechanism that generates burst oscillations remains unknown, 20 years after their discovery. Ignition conditions, flame spread, and the magnetohydrodynamics of the star's ocean all play a role. I will review the progress that we are making towards cracking this long-standing problem, and establishing burst oscillations as a tool par excellence for measuring M and R. This is a major goal for future X-ray telescopes.
Name: Wilby, Michael
Talk/Poster: Poster
Title: A “fast and furious” solution to the low-wind effect for SPHERE at the VLT
The SPHERE high-contrast imager for the VLT has recently finished its commissioning phase and is already providing exceptional results in the field of direct exoplanet imaging and circumstellar disk science. However, one of the current performance-limiting factors of the instrument is the so-called Low-Wind Effect (LWE), where the un-occulted stellar PSF gains two or more sidelobes (aka. Mickey Mouse ears) on spatial scales of 1-3 lambda/D at contrasts of 10-1 or greater. This significantly degrades the final coronagraph performance and is thought to arise from the mis-representation of characteristic instrumental wavefront errors by the filtered Shack-Hartmann Wavefront Sensor included within the SAXO extreme adaptive optics system.
We present a potential non-invasive solution to independently sense and correct the characteristic LWE wavefront in real-time, based on the “Fast and Furious” (F&F) sequential phase diversity wavefront reconstruction algorithm (Korkiakoski 2014). This uses focal-plane images available from the near-infrared Differential Tip-Tilt Sensor and crucially removes the need for artificial phase probes required by other focal-plane wavefront sensing approaches, allowing the technique to run in real time as part of the normal AO correction loop. Preliminary simulations achieve accurate recovery of the LWE wavefront and effective removal of the associated PSF lobes within a small number of F&F iterations. This work will present the results of efforts to optimise this algorithm to the LWE on SPHERE, with the ultimate goal of integration within the SAXO closed-loop environment to detect and eliminate the Low-Wind Effect as it arises.