There are 91 participants who submitted an abstract.
Name: Adams, Betsey
Talk/Poster: Talk
Title: Searching for gas-bearing dark matter halos in the Local Group
Abstract:
A long standing problem in cosmology is the mismatch between the number of low mass dark matter halos predicted by simulations and the number of low mass galaxies observed in the Local Volume. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low-mass gas-bearing dark matter halos within the Local Group. At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of 10^7-10^8 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc.
We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. These systems have been observed with the Westerbork Synthesis Radio Telescope (WSRT) to enable higher spatial resolution studies of the HI distribution. The HI morphology revealed by the WSRT data offers clues to the environment and origin of the UCHVCs, the kinematics of the HI allow the underlying mass distribution to be constrained, and the combination of spatial and spectral resolution allow the detection of a cold neutral medium component to the HI. The WSRT HI observations discriminate among the selected galaxy candidates for those objects that are most likely gas-bearing dark matter halos.
One UCHVC, AGC198606, is of particular interest as it is located 16 km/s and 1.2 degrees from Leo T and has similar HI properties within the ALFALFA dataset. The WSRT HI observations reveal a smooth HI morphology and a velocity gradient along the HI major axis of the system consistent with rotation. These properties are consistent with the hypothesis that this object is a gas-bearing low-mass dark matter halo. |
| |
Name: Aghanim, Nabila
Talk/Poster: Talk
Title: Planck latest results
Abstract:
The Planck mission delivered its ntensity full dataset early 2015. With this new data, Planck has rovided even more stringent cosmological constraints derived from the MB and from the large scale structures. In combination with BICEP and ECK2 the tightest constraints on the B-mode polarisation were also btained. The presentation will review the status of these latest results.
|
| |
Name: Albert, Joshua G.
Talk/Poster: Poster
Title: Future Detectability of Hyper Velocity Stars with Gaia
Abstract:
Hyper Velocity Stars (HVSs) are gravitationally unbound stars travelling radially away from the Galactic center (GC). Their origin, and unique trajectory make them ideal candidates for studying both the GC stellar population, as well as the shape and depth of the Galactic potential.
Currently, only 23 HVSs have been observed, however Gaia may provide the opportunity for many more HVS discoveries. We carry out an strometric analysis of HVSs and predict how many HVSs Gaia is expected to find. Our preliminary results suggest Gaia will indeed discover at least an order of magnitude more HVSs than are currently known.
|
| |
Name: Allen, Veronica
Talk/Poster: Poster
Title: Small Scale Chemistry and Kinematics of G35.20N with ALMA
Abstract:
ALMA Cycle 0 observations of G35.20-0.74 reveal a complex chemistry, including multiple complex organic species, and rotational motion with a spatial resolution of ~900AU. Interferometric images of formamide are also shown for the first time and compared to those of HNCO supporting the conclusion that they are chemically linked. |
| |
Name: Antonellini, Stefano
Talk/Poster: Poster
Title: Understanding water in protoplanetary disks
Abstract:
Protoplanetary disks are generally assumed to consist of 99% gas and 1% dust. Water is one of the main gas component and thanks to its rich spectroscopy, it can be detected in a wide spectral range from near- to far-IR.
Observations towards TTauri stars disks shows mid-IR water lines in a limited percentage of case. The fundamental ortho water line then has been detected successfully only in TW Hya. Several continuum and other spectral lines observations suggest that disks properties are quite different between objects. In our study we found how several disk properties are able to affect the water line flux in mid- and far-IR regimes and its spatial distribution.
Water is also a ""volatile"", that means, a species that can freeze onto dust grains forming ice mantle once certain conditions of gas temperature and pressure are encountered. This produces huge reservoirs of ""hidden gas"", often not directly observable. However, these reservoirs play a fundamental role in the formation of planetesimals and planets. The chemical processes happening in the midplane have timescales of millions of years, and so the ice reservoirs will develop and evolve through the lifetime of the disk. The amount of material embedded in ices potentially will feed directly (during formation) or indirectly (through impact of minor bodies) the future planets lithosphere and atmosphere. The extension of the frozen reservoirs (position of the ice lines) will affect in which regions of the disk planet formation can be faster/enhanced. |
| |
Name: Aranzana, Ester
Talk/Poster: Talk
Title: The ubiquitous rms--flux relation: from CVs to AGNs
Abstract:
Accretion is a common phenomenon in compact objects, from the supermassive black holes in active galactic nuclei (AGNs) to the stellar-mass black holes and neutron stars in X-ray binaries (XRBs), and white dwarfs in cataclysmic variables (CVs). Despite the differences between them, these systems share many observational properties such as recurrent outbursts, spectral state transitions, outflowing jets and aperiodic variability. The latter is thought to originate in the disk, and therefore studying the short and long-term variability of these systems can give insight into the geometry and physical processes occurring in the accretion disks.
The variability properties of accretion disks in XRBs have been extensively studied in X-rays, due to dedicated X-ray timing missions. For CVs and AGNs the accretion disks primarily emit in the optical and the UV. The optical variability studies can be used to compare to XRBs. Here we investigate the optical variability of a sample of CVs, which are non-relativistic objects, using high-speed multicolour photometry performed with ULTRACAM. We present the optical rms-flux relation at high frequency for 12 CVs, including magnetic CVs. This result supports the fluctuating-accretion model as the best model to explain the rms-flux relation in all accreting compact systems. Furthermore, the high frequency breaks of the power spectral densities of these CVs can be associated to viscous timescales of a geometrically thick flow, similar to what has been reported for XRBs. In addition, we explore the same properties of a sample of AGNs with KEPLER/K2. We compare the variability properties of CVs with XRBs and AGNs to better understand the physical processes occurring in the accretion disks and build a unified accretion model.
|
| |
Name: Baan, Marieke
Talk/Poster: Talk
Title: 8 tips to make media and outreach persons happy
Abstract:
"Oh no, the press is at the phone. What do I do?" Press officers Marieke Baan and David Redeker (NOVA Information Center) present eight easy tricks for researchers to deal with the press. After the interactive presentation you are not afraid of the media anymore and you know how you can help your outreach officer. Before joining NOVA in 2005 Marieke Baan was a journalist for the NOS (national public broadcaster). David Redeker worked as a spokesperson for NWO and writes for the popular science magazine Quest. |
| |
Name: Baneke, David
Talk/Poster: Talk
Title: Astronomy in the Netherlands: a history
Abstract:
Astronomy may be the oldest science, the Dutch astronomical community is relatively young. The Nederlandse Astronomenclub is approaching its first centenary; the first Astronomenconferentie was 75 years ago. In my talk I will look at several crucial moments in the history of the Dutch astronomical community – the community that will gather in Nunspeet in May. I will analyze the what made a group of researchers into a ‘scientific community’, and why that was important for the development of astronomical research. In the process, I will shed light on some of the peculiar characteristics of Dutch astronomy in the last hundred years.
This talk is based on my book De ontdekkers van de hemel: de Nederlandse sterrenkunde in de twintigste eeuw.
|
| |
Name: Bilous, Anna
Talk/Poster: Talk
Title: LOFAR Census of Non-Millisecond Pulsars
Abstract:
The first results of LOFAR census of normal (non-millisecond) pulsars are presented. During January-May 2014, 194 normal pulsars (almost all known sources with |Gb|>3 deg and dec>10 deg) were observed with LOFAR high-band antennas in the frequency region of 110 – 188 MHz. Accumulated data set will allow us to study the characteristics of pulsars as a population, instead of on a source-by-source basis. Through these observations we will be able to probe the interstellar medium through measurements of dispersion, scintillation, scattering and Faraday rotation; and the enigmatic pulsar emission mechanism through measurements of broadband spectra, polarisation profiles, and analysis of single pulses. I will present the first results of data reduction, including dispersion measures, fluxes and average profiles of the detected pulsars. |
| |
Name: Bonnerot, Clément
Talk/Poster: Poster
Title: Disc formation from tidal disruptions of stars on eccentric orbits
Abstract:
The potential of tidal disruption of stars to probe otherwise quiescent supermassive black holes cannot be exploited if their dynamics is not fully understood. So far, the observational appearance of these events has been derived from analytical extrapolations of the debris dynamical properties just after the disruption. By means of hydrodynamical simulations, we investigate in this paper the subsequent fallback of the stream of debris towards the black hole for stars on eccentric orbits. We demonstrate that the debris form a disc due to relativistic apsidal precession which causes the stream to self-cross. The circularization timescale varies between 1 and 10 times the period of the star, being shorter for more eccentric and/or deeper encounters. The self-crossing of the stream leads to the formation of shocks which increases the thermal energy of the debris. If this thermal energy is efficiently radiated away, the debris settle in a narrow ring at the circularization radius. It then proceed to accrete viscously at a super-Eddington rate while puffing up due to radiation pressure. If instead cooling is impeded, the debris form an extended torus located outside the circularization radius. Viscous accretion occurs faster in this case which causes the torus to be accreted at a super-Eddington rate while forming. For stars on parabolic orbits, we expect circularization to occur in at most a few periods of the most bound debris with the same effect of the cooling efficiency on the structure of the disc. |
| |
Name: Borghese, Alice
Talk/Poster: Talk
Title: Discovery of a narrow phase-dependent spectral feature in the XDINS RX J0720.4-3125
Abstract:
In this talk I would like to report the discovery of a narrow phase-dependent absorption feature in the X-ray spectrum of the nearby X-ray Dim Isolated Neutron Star RX J0720.4-3125. This feature was discovered performing a detailed phase-resolved spectral analysis using XMM-Newton observations which cover 12 years. The line seems to
be stable in time over this timespan and is present in 20% of the pulsar rotation. Because of its narrow width and its strong dependency on the rotational phase, the spectral line is probably due to proton cyclotron absorption in a ~10^14 G confined magnetic structure (with a
field strength about 7 times the dipolar field of this pulsar).
|
| |
Name: Brentjens, Michiel
Talk/Poster: Talk
Title: The solar eclipse through radio eyes
Abstract:
At March 20 earlier this year, a partial solar eclipse was visible from the Netherlands. That is, for those that could actually see through clouds. Fortunately we have a major radio telescope that can! I'll show the LOFAR high band movie that we created and live-tweeted during the eclipse, present the best-calibrated images we made afterwards, and point out interesting features in the solar corona and the brightness distribution on the moon. |
| |
Name: Brinkerink, Christiaan
Talk/Poster: Talk
Title: What shape is Sgr A*? Constraining model predictions with VLBI closure phases
Abstract:
The radio source associated with the supermassive black hole at the center of our Galaxy (Sagittarius A*) has not been resolved so far, and the behaviour of the emitting gas has been a subject of debate for a long time. The spectrum of Sgr A* in radio strongly suggests the presence of some kind of outflow, motivating the choice for a compact jet model. Studying the intrinsic shape of Sgr A* requires measurements with extremely high resolution to be made, and imaging requires good UV coverage which is not often available. However, closure phase measurements done at 1.3mm and 3.5mm can already help us in constraining the source geometry. I will discuss the source geometry constraints we find from existing measurements, and present predictions for future measurements based on this. |
| |
Name: Burkert, Andreas
Talk/Poster: Talk
Title: Watching a Little Gas Cloud on its Way into the Galactic Supermassive Black Hole
Abstract:
The Galactic center is one of the most fascinating and extreme places in the Galaxy. Harboring a supermassive black hole with a mass of order 4 million solar masses it experiences cycles of activity and star formation, separated by periods of quiescence that last of order a million years. The Milky Way's SMBH currently is inactive. However a small, diffuse gas cloud (G2) has recently been detected on an orbit almost straight into the Galactic SMBH. In the middle of 2013 G2 started to pass the SMBH at a small distance of just 2000 Schwarzschild radii, corresponding to 20 light hours. Most of its emission at that time was still strongly redshifted. In 2014 part of it emerged on the opposite, strongly blue-shifted side, past pericenter. In agreement with numerical simulations the ionized gas of G2 had been stretched by the enormous tidal fields over more than 15,000 Schwarzschild radii around the pericenter. Depending on its nature G2 will now begin to break up and feed the SMBH, possibly triggering a phase of AGN activity. The next years will therefore provide a unique opportunity to investigate directly the processes that drive and regulate gas accretion onto the Galactic SMBH. In addition, G2 turns out to be a powerful probe of the structure and composition of the extreme interstellar environment in the Galactic center.
This talk will summarize the observations and various numerical simulations of G2's evolution. The existence of such a tiny, cold gas cloud in the hostile vicinity of the SMBH raises numerous fascinating questions related to its structure. Where did it come from and where will it go? Why is it on such a highly eccentric orbit? Which physical processes constrain its properties like its size, mass, density, temperature and geometrical shape? Is G2 a diffuse gas clump that originates from winds of high-mass stars in the surrounding stellar disk or is it the atmosphere of an evaporating, invisible protostellar disk, surrounding a young low-mass stars.? Is it a tidally disrupting star? Or is it something completely different? How many clouds like G2 are currently orbiting Sgr A* and how do they affect its activity and gas accretion rate?
It is rare in astronomy that theoretical models and numerical simulations can be validated directly by observations. G2 is such a unique case. Like comet Shoemaker Levy's 1994 collision with Jupiter, the big challenge has started for theoretical astrophysics to predict the outcome of G2's close encounter with the SMBH in the years beyond 2015, before it is actually seen. |
| |
Name: Cheng, Zheng
Talk/Poster: Poster
Title: The cooling of the neutron star in EXO 0748-676 in quiescence with XMM-Newton
Abstract:
The cooling of the neutron star in EXO 0748-676 in quiescence with XMM-Newton
We present the spectral analysis of four XMM-Newton observations of the neutron-star low-mass X-ray binary 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 per cent confidence upper limit of 1 per cent to the contribution of the power law to the total flux of the source in the 0.5-10.0 keV range.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.
|
| |
Name: Daprà , Mario
Talk/Poster: Talk
Title: Using molecular hydrogen to constrain a cosmological variation of the proton-to-electron mass ratio
Abstract:
A constraint on a variation of the proton-to-electron mass ratio (mu) is derived from the analysis of molecular hydrogen transitions toward the background quasar J1237+0647. The system is composed of three absorbing clouds where 114 H2 and HD absorption features are detected. A comprehensive fitting method was used to fit all the absorption features at once and it delivers a constraint on a variation of the proton-to-electron mass ratio of dmu/mu = (0.6 ± 7.1) × 10^(−6), which is consistent with a null variation of mu for a look-back time of 11.4 Gyrs. |
| |
Name: de Boer, Jozua
Talk/Poster: Talk
Title: SPHERE/ZIMPOL imaging of the circumstellar disk of BP Psc
Abstract:
BP Psc was classified as a Classical T Tauri Star (CTTS), but recent studies suggest that it is more likely to be an evolved star. This uncertainty in our knowledge of the evolutionary stage of BP Psc has led to diversity of interpretations of its circumstellar disk structure including suggestions of ongoing or recently completed planet formation. We observed BP Psc with VLT/SPHERE/ZIMPOL during the Science Verification period. The disk is clearly detected in polarized intensity as well as in total intensity, for the first time at visible wavelengths. A comparison of radiative transfer models and the observed polarized intensity image reveals a disk at an inclination where the direct starlight grazes the disk surface. This configuration is extremely sensitive to disk irregularities transiting the star, which might explain the observed variability of BP Psc and constrain its distance and evolutionary stage. |
| |
Name: de Koter, Alex
Talk/Poster: Talk
Title: Are all massive stars part of multiple systems?
Abstract:
Multiplicity is a fundamental observable property of massive O type stars and offers a promising way to discriminate between massive star formation theories. It has been known for some time that the majority of these stars, with initial masses larger than 15 Msun, have at least one companion detected either through spectroscopy or through imaging techniques. Unfortunately, the techniques mentioned fail to provide a comprehensive view of O star multiplicity over the full separation range, spectroscopy allowing to detect only the closest systems and imaging only the widest systems. Companions at intermediate separations, between 1 and 100 mas, remain mostly unknown due to intrinsic observational limitations. The Southern MAssive Stars at High angular resolution survey (SMASH+) of galactic O stars was designed to fill this gap, applying interferometric techniques. We find that the fraction of dwarf O stars — which one may think of as representing the youngest O star population — that have a bound companion reaches 100% at 30 mas while the average number of physically connected companions within 8 arc seconds exceeds two. This demonstrates that massive stars form nearly exclusively in multiple systems. I will discuss some of the implications of these results for our understanding of massive star formation. |
| |
Name: Deller, Adam
Talk/Poster: Talk
Title: PSRPI: 50+ new distances to radio pulsars
Abstract:
To investigate pulsar properties like luminosity and transverse velocity, one needs an accurate distance. A distance can be estimated for any radio pulsar based on the dispersion measure, but the result is hugely uncertain for any individual source: errors of a factor of 5 or more have been seen! The ideal solution is a model-independent distance, which is usually obtained by a measurement of annual geometric parallax. Very Long Baseline Interferometry can be used to make such measurements, with accuracies approaching 10 microarcseconds: equal to the best expected GAIA results, meaning a 10% distance error at 10 kpc. I will report on the largest VLBI parallax program ever undertaken (PSPRPI), which has measured over 50 new pulsar parallaxes, as well as several other recently concluded projects. Highlights include several binary millisecond pulsars for which the distance allows a thorough investigation of the white dwarf companion, and revised estimates of the Galactic electron density distribution and pulsar velocity distribution. |
| |
Name: Enriquez, J. Emilio
Talk/Poster: Talk
Title: Searching for Extraterrestrial Intelligence in the NL.
Abstract:
Although no evidence for life has yet been found in any environment outside the Earth, we now have ample evidence that the conditions we believe necessary for life to arise are ubiquitous in the Milky Way. Water and complex chemistry appear to be common, and the most recent results from exoplanet research indicate that planets in the habitable zone of their host star are common. The pressing question yet to be answered is whether or not life has indeed arisen elsewhere in the universe, and further whether that life may have evolved intelligence as occurred on Earth.
It is well established that certain types of radio emissions could be a superb probe of extraterrestrial technology, and by proxy, would reveal intelligent civilizations capable of producing technology. Radio emission narrower than 5 Hz is, as far as we know, generated only by arti cial sources. These types of emissions transit the interstellar medium readily, are energetically cheap to produce and are relatively easy to detect with current technology. Narrow-band radio emission is easily discriminable from background astrophysical sources of electromagnetic radiation, and thus possesses merit as a possible mechanism for an intentional signal from an advanced civilization as well.
The Search for Extraterrestrial Intelligence (SETI) in The Netherlands is an ongoing effort by different groups. LOFAR, Jive and the Dwingeloo radiotelescope are used for this effort. Here, I will describe the recent SETI research of our group, and give a review on other SETI efforts in The Netherlands. I will describe the different experimental methods, recent observational results and plans for future SETI observations. |
| |
Name: Franse, Jeroen
Talk/Poster: Poster
Title: Update on the 3.5 keV X-ray line from galaxies and cluster
Abstract:
I will present a review of the observation of the 3.5 keV X-ray line in galaxies and galaxy clusters, which is a good candidate dark matter decay signal, and give an update on recent and forthcoming work regarding the study of its origin. |
| |
Name: Frieswijk, Wilfred
Talk/Poster: Poster
Title: The LOFAR Long Term Archive
Abstract:
TBD |
| |
Name: Giese, Nadine
Talk/Poster: Talk
Title: 3D characterization of neutral hydrogen in galaxies
Abstract:
Asymmetries in the neutral hydrogen (HI) gas content of galaxies are thought to be indicators for gas accretion and gas removal processes that are of fundamental importance for galaxy formation and evolution. Upcoming large blind HI surveys (e.g. with Westerbork/APERTIF) will provide data for tens of thousands of galaxies for a study of these asymmetries in a proper statistical way. Due to the large number of expected sources it is not feasible anymore to manually find and characterize galaxies in 3D HI data cubes. Furthermore, a detailed modeling for every single object is too time consuming. We are working on non-parametric methods that can derive galaxy properties in a fast, automated and reliable way. Since studies so far have only used 2D maps generated from the data cubes, we are especially interested in developing 3D methods that use the full information along the third axis, the frequency or velocity axis. We will show what the limitations of 2D non-parametric methods are and how to correct the results for effects like noise in the data. Additionally, we will give an outlook on how the use of the full 3D information can improve the estimates that 2D methods deliver and help distinguish between different kinds of asymmetries (morphological vs. kinematic). |
| |
Name: Goddi, Ciriaco
Talk/Poster: Talk
Title: Imaging the event horizon of Sgr A* with BlackHoleCam
Abstract:
The center of the Galaxy hosts the closest and best-constrained supermassive black-hole candidate in the universe, Sgr A*. The theory of general relativity (GR) predicts the appearance of a black hole shadow, which is a lensed image of the event horizon. This shadow can be resolved by upcoming very long baseline radio interferometry experiments at mm wavelengths and allows us for the first time to test GR on an event horizon scale with imaging techniques. In this talk I will review the current status of the experimental efforts towards imaging Sgr A* with the Event Horizon Telescope (EHT). In particular, I will focus on the european efforts towards the EHT with BlackHoleCam (BHC), an ERC synergy grant funded project to support global mm-VLBI and pulsar observations as well as to develop GR-MHD models. |
| |
Name: Gotberg, Ylva
Talk/Poster: Poster
Title: Binary products and their impact on the radiative feedback of massive stars populations
Abstract:
Recent studies showed that young massive stars are most often found in binary systems. These binaries are often close enough to interact through Roche Lobe overflow as a result of the evolutionary expansion of the stars. Stars can be stripped, gain mass or even merge, drastically changing their further evolution and finally fate. This raises the question what the consequences of binarity are for the properties of stellar populations in Galaxies throughout the Universe.
We use the stellar evolutionary code MESA to investigate the effect of envelope stripping by the companion. This leads to the formation of hot and compact naked helium stars that are potentially interesting sources of ionizing radiation. We compare their radiative feedback with the contribution of massive main sequence stars and Wolf-Rayet stars, by creating grids of stellar and binary evolutionary models. |
| |
Name: Grin, Nathan
Talk/Poster: Poster
Title: Testing rotational mixing in O-type giants and supergiants in 30 Doradus
Abstract:
One of the major uncertainties in massive star evolution theory is the role of rotationally induced mixing, which might lead to quasi-chemically homogeneous evolution.
The most powerful observational diagnostic to challenge current theories and constrain the mixing efficiency, is the nitrogen surface abundance of a homogeneous sample of rotating massive stars. The VLT-FLAMES Tarantula Survey (VFTS) is a multi-epoch study on over ~300 massive O-type stars in the 30 Doradus (30 Dor) region of the LMC.
Here we determine the surface nitrogen abundance of the spectroscopic single of the O-type giant, bright giants and supergiant stars in the VFTS (~70 stars).
Interestingly, we found that the most nitrogen enriched stars are slow rotators. This counters the theory of rotational mixing and thus challenges altogether our understanding of it.
As a consequence our study will allow us to test the implementation of rotational mixing in massive star evolutionary models, to calibrate the mixing efficiency and to guide further theoretical development in single and binary massive star evolution. |
| |
Name: Guo, Difeng
Talk/Poster: Poster
Title: The Sco-Cen OB association and the Gould Belt
Abstract:
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. |
| |
Name: Hagen, Jorrit
Talk/Poster: Poster
Title: Axisymmetric dynamical orbit-based models of dwarf spheroidal galaxies
Abstract:
In the current cosmological LCDM model, nearly one quarter of the energy density of the Universe is due to dark matter, however we still do not know what cold dark matter is. Dark matter dominated systems, such as the dwarf spheroidal satellite galaxies of our Milky Way, can be used to put constraints on the nature of dark matter.
The goal of this work is to measure the mass content, dark matter density profile and internal orbital structure of the Sculptor Dwarf Spheroidal Galaxy, using the Schwarzschild's orbital superposition method. Most work so far has assumed that dwarf spheroidal galaxies and their host halos are spherical, whereas we already know from the light distribution this is not the case. Because of this, we plan to use the Schwarzschild method in the axisymmetric regime to model these systems. The Schwarzschild method uses a complete set of orbits as building blocks for the system that is being studied. The combination of orbits needed to match the observations, will result in the distribution function of the system.
We first study a composite system that results in a logarithmic potential with the same flattening in the stars as in the dark matter component, and which has a simple analytic distribution function. We use this model to test how well our Schwarschild method can constrain the global parameters of the potential and the stellar dynamical properties.
In this poster we show that our method can reproduce the light distribution and the stellar kinematics of such a mock galaxy. Furthermore we demonstrate how well the input values of the characteristic parameters of the potential are recovered for datasets of different sizes. In the future, we will test our method using different axisymmetric potentials and we will apply the Schwarzschild method to actual data of the Sculptor Dwarf Spheroidal Galaxy. |
| |
Name: Hakim, Kaustubh
Talk/Poster: Poster
Title: High pressure-temperature experiments to probe the interior of carbide exoplanets
Abstract:
Recent discoveries of rocky exoplanets in chemically diverse planetary systems suggest that these planets might contain significantly higher amounts of lighter elements, specifically carbon, than the planetary bodies in our own solar system. This complicates our understanding of the interior properties of these planets since those properties are often based on the extrapolation of knowledge about the terrestrial planets which are carbon deficient. To address this complication, we are performing high-pressure, high-temperature laboratory experiments to probe the interior of rocky exoplanets with and without carbon. At the high pressure laboratory of VU University Amsterdam, we aim to study the physical and chemical properties of minerals and melts that could be present in the mantle and core of these planets. We plan to 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 at the Netherlands National Electron Microprobe facility. For our first experiment at high pressure and high temperature without carbon, we find the segregation of molten iron into metallic blobs surrounded by silicate minerals and melt, which is similar to previous findings for terrestrial planets. |
| |
Name: Hartke, Johanna
Talk/Poster: Poster
Title: New optical spectroscopy of Draco and Ursa Minor
Abstract:
We present new optical spectroscopy of individual red giant branch stars in the dwarf spheroidal galaxies Ursa Minor and Draco. While Draco appears to have a perfect, undisturbed stellar distribution, Ursa Minor shows signs of tidal disruption. The two galaxies are otherwise similar in terms of mass, extent, and distance, making them an interesting pair to analyse using the same methods. We observed several hundred stars in the CaII triplet region using the AF2-WYFFOS fiber spectrograph on the William Herschel Telescope in May 2014, with follow-up observations scheduled for May 2015. These data have been pipeline-processed at CASU in Cambridge using prototype WEAVE processing. This is one of the first major surveys that also include metallicity measurements for these dwarf galaxies. We will apply orbit-based Schwarzschild modelling to the velocity data in order to constrain their (dark) matter distribution.
|
| |
Name: Heida, Marianne
Talk/Poster: Talk
Title: Dynamical Mass Measurements of ULXs in the Near-Infrared
Abstract:
Are ultraluminous X-ray sources powered by stellar or intermediate mass black holes? To answer this question we need reliable mass measurements of these systems. The best way to do this would be to measure the radial velocity curves of the companion stars and thus derive the mass functions for these black holes. This has proven to be very difficult for ULXs because the optical light from these systems is dominated by the accretion disc. However, for ULXs with red supergiant donor stars, that are intrinsically bright in the near-infrared it may be possible to measure their radial velocity curves in that part of the spectrum. We have conducted a survey of nearby ULXs to search for near-infrared counterparts. Of our 62 targets, 11 have a counterpart that could potentially be a red supergiant (Heida et al. 2014). Spectroscopic follow-up of some of these candidates has revealed that a few are indeed red supergiants, for which we will now attempt to measure radial velocity curves. |
| |
Name: Hess, Kelley
Talk/Poster: Talk
Title: Cold gas, star formation, and substructure: Tracing the Mass Assembly of the Antlia Cluster
Abstract:
The Antlia Cluster is the third most nearby cluster after Virgo and Fornax. The cluster is a dynamically young structure and its proximity presents us with a valuable opportunity for detailed study of galaxy and group accretion onto clusters. We present a deep HI mosaic combined with mid-infrared star formation tracers, and the employment of statistical kinematic methods to distinguish substructure within the cluster and identify infalling galaxy groups. Through the presence of \hi\ and on-going star formation, we rank the substructures with respect to their relative time since accretion onto Antlia to unravel the cluster's assembly history. |
| |
Name: Hessels, Jason
Talk/Poster: Talk
Title: New Kids on the Block: Meet the Transitional Millisecond Pulsars
Abstract:
In the last few years, a new class of neutron star binary has been discovered which transitions between states as a radio millisecond pulsar and a low-mass X-ray binary (either in quiescence or outburst).
These so-called "transitional millisecond pulsars" (tMSPs) are showing us new phenomena not previously observed in accreting neutron star X-ray binaries: e.g. enhanced gamma-ray emission, suprisingly bright radio emission from an outflow, and accretion-induced coherent X-ray pulsations at quiescent level luminosity. As such, they hold the promise of better understanding accretion onto a magnetized object - a situation which occurs in a broad range of astrophysical contexts.
They are also helping us map the "pulsar recycling" scenario, which is responsible for spinning up some neutron stars to millisecond rotational periods. I will highlight some of the discoveries our group has made in the last two years, and link the tMSPs to other types of accreting compact objects. |
| |
Name: Hutten, Marten
Talk/Poster: Poster
Title: Faint end photometry of the Fornax Cluster with OmegaCAM on the VST
Abstract:
As part of the Fornax Deep Survey we have obtained deep photometric data of an 11 square degrees field in the Fornax cluster in 4 different bands, u, g, r, and i using OmegaCAM on the VST. In the process of separating nearby, low surface brightness dwarf galaxies from distant, high surface brightness large galaxies, we have fitted a number of objects with the program GALFIT to obtain morphological parameters in the 4 bands. Apart from a number of detailed fits, we also show the minimum radius for which we can reliably use this method of separating cluster galaxies from background objects, and in this way determine the low-end part of the luminosity function of the Fornax Cluster. |
| |
Name: Jacobs, Bob
Talk/Poster: Poster
Title: Characterising the Galactic Transient & Variable Optical Skies
Abstract:
In 2017 wide-field optical telescopes, such as BlackGEM, will come online with an aim to measure the optical emission from mergers of neutron stars and black holes. Just before merger, these binaries will also emit in gravitational radiation, measurable by newly upgraded versions of gravitational wave detectors (Virgo, LIGO). Gravitational wave detectors can only localise the mergers from tens to hundreds of square degrees on the sky. Within these large areas of the sky, we expect many other transient and variable sources. By characterising these other astrophysical false positives, we are developing a search strategy for different telescopes in order to pinpoint, discover and measure these fast and elusive mergers in the optical.
Within the framework of BlackGEM, this bachelor's project aims to develop a search strategy to deal with the unknown number of Galactic transients and variable sources that may mimic a neutron star binary merger. I have developed a python-based Monte-Carlo simulation of different classes of Galactic variables and transients using Galactic population density profiles. By implementing a suite of empirical light curves, I show how we can probabilistically classify these Galactic sources for BlackGEM with different filters and cadences as it scans the skies. |
| |
Name: Janssen, Gemma
Talk/Poster: Talk
Title: Detecting gravitational waves with a pulsar timing array
Abstract:
By using high precision timing observations of an array of millisecond pulsars, extremely small signals originating from the effect of gravitational waves passing pulsars and the Earth can be detected in the arrival times of the pulses of the pulsars.
I'll give a summary on the recent work by the European and International Pulsar timing array collaborations, and give an outlook of detecting gravitational waves in the near future and moving from a first detection to gravitational wave astronomy when the SKA comes online. |
| |
Name: Jaodand, Amruta
Talk/Poster: Talk
Title: Is the missing link pulsar J1023 spinning up or down?
Abstract:
Millisecond pulsar formation through the recycling mechanism proposed by Alpar et. al (1982) was confirmed by the discovery of the missing link X-ray binary/radio millisecond pulsar transition system PSR J1023+0038 (J1023; comprising a pulsar with spin period of 1.7ms and a low-mass companion of ~0.2 Msun).During the recycling phase the pulsar is spun up through channeled accretion via Roche lobe overflow from it's companion; the underlying accretion mechanism remains elusive. However, with discovery of J1023 and two other transitional millisecond pulsar systems (XSS J12270-4859 and IGR 1824-2452I) in the last decade, we now have means to probe the questions related to accretion mechanisms responsible for the formation of such systems employing a multi-wavelength approach. X-ray observations of J1023, after it's transformation to an accretion-disk-dominated state in June 2013, revealed a variable X-ray luminosity intermittently switching between L_x~10^32 erg/s for the 'low mode' and Lx~10^33 erg/s for 'high mode'. Remarkably, only the high mode shows coherent pulsations at the spin period of the pulsar. These pulsations, present for roughly 80% of the time, are stable in brightness on timescales of months to at least a year. Using these pulsations to track the spin evolution of J1023 during its current accretion state holds the potential to explain the underlying accretion mechanism. We are using recent XMM-Newton DDT observations to measure J1023's current spin period. We have taken a logarithmically spaced set of four observations, and have easily detected the pulsations first reported in previous observations (Archibald et al. 2014). We have also obtained preliminary period estimates. I will present the detailed outcome of this observing campaign, which we hope will tell us whether J1023 experiences a net spin up or spin down in it's accreting phase. |
| |
Name: Kenworthy, Matthew
Talk/Poster: Talk
Title: METIS: detecting and characterising exoplanets in the thermal infrared
Abstract:
METIS, the Mid-infrared E-ELT Imager and Spectrograph, will be one of the three first instruments on the 39m European Extremely Large Telescope (E-ELT). METIS is the largest project which has ever been undertaken by NOVA, and is expected to see first light in 2025. Focusing on highest angular resolution and high spectral resolution in the 3 - 19 micrometer range, METIS will offer a unique combination of adaptive optics and coronagraphy for high contrast imaging with R=100,000 integral field spectroscopy. While the science case covers a broad range from Solar system objects and protoplanetary disks to local AGN and starburst galaxies at intermediate redshifts, a strong focus lies on the formation of exoplanets, their detection and characterization. In this paper I will discuss the main science questions concerning exoplanets, which METIS will be able to address, as well as the technical means that are required to enable these discoveries. |
| |
Name: Khanna, Shourya
Talk/Poster: Poster
Title: Probing the photoionized outflows and variability in the NLS1 galaxy Arakelian 564: An XMM-Newton view
Abstract:
Arakelian 564 is the brightest Narrow-Line-Seyfert galaxy in the 2-10 keV band. We present a combined analysis of XMM X-ray observations of Ark 564 taken between taken 2000 and 2011. We have carried out high resolution spectroscopy on the resultant high signal-to-noise stacked spectrum and have identified broad oxygen and nitrogen lines possibly from relativistic emission due to a non-rotating central black hole. In addition we detect three warm absorbers and provide improved constraints on the location of these clouds with respect to the source. Long term variability and the response of gas to source luminosity are found to be chaotic although using an observed 20 day variability we estimate the lower limit to the emission zone at 20 light days. The outflow and location constraints will be used to estimate the kinetics of the source in the context of AGN feedback.
|
| |
Name: Kokotanekov, Georgi
Talk/Poster: Talk
Title: Feedback galaxy clusters in MSSS
Abstract:
In this project we aim to expand the existing relation between AGN jet power and radio power to lower radio frequencies. For this purpose we use data from LOFAR’s Multifrequency Snapshot Sky Survey (MSSS). We study the observations of 15 galaxy clusters, part of the famous Birzan sample of known bright, nearby, and resolved feedback systems, in order to measure their total flux. We aim to investigate how radio luminosity at 150 MHz correlates with cavity power computed from X-ray data.
In this talk I will present my current progress on the reprocessing of MSSS data in order to obtain higher quality images and study the diffuse radio emission in the clusters of interest. |
| |
Name: Kondratiev, Vlad
Talk/Poster: Talk
Title: LOFAR Census of Millisecond Pulsars
Abstract:
We report on the detection of 48 millisecond pulsars (MSPs) out of 75 observed so far with LOFAR in the frequency range of 110-188 MHz. This is the largest MSP sample ever observed and detected with a single radio telescope at these low frequencies. We present profiles of the detected MSPs and flux density measurements and compare them to published data from higher frequencies to examine their spectral behavior. We discuss MSP detectability, their spectra, profile evolution and dispersion measure variations. |
| |
Name: Koumpia, Evgenia
Talk/Poster: Talk
Title: Thermal balance in S140: Mysterious fine structure lines as mapped with GREAT/SOFIA.
Abstract:
Trying to understand the gas cooling balance in the S~140 star forming region we map the main fine structure lines of
[OI] and [CII] GREAT/SOFIA and combine them with previous ground-based observations of molecular lines.
While previous studies and observations make the IRS1 a well known main heating source of dust and large scale gas
visible in continuum, PAH emission, and many molecular lines,
the new GREAT/SOFIA data reveal that the main cooling lines peak at a position north of IRS1 and closer to the less massive and five times less
luminous cluster IRS2. We attempt to identify the origin of that peak by studying the spatial and velocity distribution of the different species.
We try to distinguish between a possible ionized outflow origin or local column density effect. For the outflow scenario we need to consider the
already known ouflow from IRS1 (Maud et al. 2013), which points west of IRS2 and it cannot fully explain the observations.
We use the higher resolution [OI] observations to estimate the emitting source size to within 5.5 arcseconds (0.02pc).
A density of $10^4$~cm$^{-3}$ can explain the observed [OI]/[CII] ratio while it fails when it comes to the the total luminosity
for both lines that require a much higher density. |
| |
Name: Lahuis, Fred
Talk/Poster: Poster
Title: Science Opportunities with the James Webb Space Observatory
Abstract:
The NASA James Webb Space Telescope (JWST) is the next major infrared space mission scheduled for a 2018 launch. On board is a suite of four sensitive near- and mid-IR instruments. Combined with the collecting power and spatial resolution of its 6.5 meter dish this provides a huge discovery potential ranging from searches for the first light after the Big Bang to the characterization of planets around stars in our local Universe. One of the instruments is the European/US Mid-Infrared Instrument (MIRI) offering imaging, coronagraphy and low and medium resolution spectroscopy (LRS and MRS) between wavelengths of 5 to 28,7 microns. Dutch science interest has a strong focus on spectroscopy. In support of this NOVA, the Netherlands Research School for Astronomy, designed and built the Spectrometer Main Optics Module (SMO) for the medium resolution spectrometer. Most of the work for the SMO was performed at ASTRON in collaboration with TNO/TPD for the optical design. MIRI was the first instrument delivered to NASA in 2012. All four instruments are since integrated into the ISIM (Integrated Science Instrument Module) which is currently being prepared for a third and final cryo-vacuum test before the ISIM will be integrated with the OTE (Optical Telescope Element) to progress to a new phase of the mission preparation.
In this poster we will highlight the MIRI science capabilities and observing opportunities. As an illustration we provide cases from the provisional MIRI guaranteed time observing program, in which has the Dutch MIRI team has a strong representation. We will also show the involvement and activities of the Dutch MIRI team in the MIRI instrument characterization, software development and overall mission preparation.
|
| |
Name: Liska, Matthew
Talk/Poster: Talk
Title: Using GPUs in 3D general relativistic MHD simulations on workstations and on supercomputers
Abstract:
Eight years ago NVIDIA introduced the CUDA framework that made it possible utilize GPUs designed for computer graphics for general purpose (scientific) computing. Since then the Khronos group followed with a competing framework called OpenCL. These GPUs can offer several orders of magnitude of improved performance in relation to CPUs, whose performance stagnated since 2011, after which Intel failed to provide IPC performance improvements consistent with Moore's law. Especially in non self-gravitating grid based codes such as the 3D GRMHD HARM code GPUs can offer 2 orders of magnitudes improved performance in relation to single CPU cores and provide better scaling across multiple nodes on supercomputers as well. This makes it possible to, for the first time, perform extended 3D runs with high resolution (1000x1000x1000 pixels) and sustained turbulence in general relativistic MHD simulations for accretion disks and jets.
During this talk I will first give a brief overview of the recent advances in GPU computing and the trends in near future, both in relation to the present and future hardware (HBM memory, NVLink and accelerators such as Xeon PHI) and software (OpenCL vs CUDA vs OpenACC). Then I will show the performance improvement I achieved in my hybrid OpenCL-MPI 3D version of the HARM code and the (improved) scaling across multiple nodes, which is very good for the GPU version of the code. I will also provide a performance comparison between AMD and NVIDIA GPUs, which shows that the often neglected AMD GPUs may provide several factors better performance at a lower cost . Then I will discuss in which cases (low overhead and ECC error tolerant) it may be OK to use the non-professional but the much cheaper 'gaming'-grade GPUs. I will finish my presentation by showing that it is possible to build GPU based workstation costing 6000-8000 Euros, which performs much better than a 1000 core cluster costing several tons at a resolution of 350x350x350 pixels. |
| |
Name: Lyu, Ming
Talk/Poster: Talk
Title: Investigating spectral and timing properties of the mHz QPOs in the low-mass X-ray binary 4U 1636-53
Abstract:
In this work we investigated the spectral and timing properties of the mHz QPOs in XMM-Newton observations of 4U 1636-53 to have a closer look into the mechanism behind the mHz QPO. Using XMM-Newton and RXTE observations, this is the first time that we are able to apply a wide energy band (0.8-100 keV) spectral analysis in the mHz QPO cycle. Besides, we explored the possible relation between the QPOs and the associated X-ray bursts. We find that there is a moderate correlation between QPO frequency and neutron star surface temperature. Moreover, all bursts associated with the QPOs are short, bright and energetic, indicating a strong connection bewteen mHz QPOs and He-rich bursts. |
| |
Name: Maccagni, Filippo
Talk/Poster: Talk
Title: The triggering of radio AGN: the intriguing case of GPS source PKS1718-649
Abstract:
Nuclear activity in radio AGN is thought to be connected with the presence and the kinematical properties of the gas in the circum-nuclear regions. In particular, in compact, young radio galaxies, the HI, inflowing or outflowing from the nucleus, may trigger and regulate the fuelling of the radio activity.
The GPS source PKS 1718-649 is a crucial representative case, since there is only a handful of objects where the HI has been studied in connection to the triggering of the radio AGN. PKS 1718-649 is the closest GPS source, it is very young (~10^2 years) and it is hosted by an S0 galaxy with a massive regularly rotating HI disk. The kinematics of the HI disk exclude a major accretion event as the trigger of the nuclear activity. The HI detected in absorption against the very compact nucleus (<2 pc) suggests that the AGN has been triggered by a small-scale phenomenon in the inner regions of the galaxy. This hypothesis is strengthen by SINFONI IFU observations of the warm H2 in the central regions of this galaxy and by the variability of the low band spectral continuum.
The study on PKS 1718-649 is being extended to the compact sources of the shallow HI absorption survey we carried on with the WSRT. There we observed the sample over 100 radio sources, and in compact CSS and GPS sources the HI is more often detected and the absorption lines show that it is more unsettled, suggesting a strong interplay between the radio plasma and the ISM in the first phases of the activity. |
| |
Name: Martinez Barbosa, Carmen Adriana
Talk/Poster: Talk
Title: Solar siblings in the Gaia era
Abstract:
The high eccentricities and inclinations observed in the orbits of the Edgeworth-Kuiper belt objects as well as the radioactive isotopes found in the meteorite fossil record are some of the imprints found in the solar system that suggest the Sun was born in an open cluster 4.6 Gyrs ago. We perform realistic simulations to trace the motion and disruption of the Sun's birth cluster in the Milky Way. We aim to predict the current spatial distribution of the solar siblings in terms of different Galactic parameters and the possibility of fi nding these stars in the Gaia catalogue by using only positional and kinematic information.
|
| |
Name: Menu, Jonathan
Talk/Poster: Talk
Title: Evolving evolutionary scenarios for disks around intermediate-mass young stars
Abstract:
During the past decade, the MID-infrared Interferometric instrument (VLTI/MIDI) has given us new insights in the geometry and dust composition of the disks around young stars. However, most studies focused on at most a handful of objects, which complicates the interpretation of the results of individual studies in terms of disk statistics.
The aim of this project is to investigate a statistically relevant sample of intermediate-mass young stars. We collected the archival MIDI data of more than 30 objects and reduced and calibrated the data in an automatized way.
Essentially all observations show that the disks around these objects are resolved. We use simple geometric disk models for analyzing the data and compare characteristic sizes and colors. Radiative-transfer models are used for interpreting the mid-infrared signatures. The observations confirm that many disks around intermediate-mass young stars have a transitional nature, i.e., they have large gaps. Though other mechanisms might explain the presence of these gaps, transitional disks have often been associated with the ongoing formation of massive planets. Our study reveals a new population of flat disks with small gaps in the inner disks. This finding challenges existing evolutionary scenarios, and we discuss whether/how these objects may represent a missing link in the current observational picture of intermediate-mass young stars.
|
| |
Name: Mernier, Francois
Talk/Poster: Poster
Title: Abundance distribution in the hot intra-cluster gas of Abell 4059
Abstract:
Using the EPIC and RGS data from a deep (200 ks) XMM-Newton observation, we investigate the abundances of nine elements (O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni) of the intra-cluster medium (ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a deep analysis of the cluster core, a careful modelling of the EPIC background allows us to build radial profiles up to 12' (~650 kpc) from the core. The abundances of Fe, but also Ne, Si, S, Ar, Ca, and O (not shown here) are all peaked towards the core. The elements Fe and O are still significantly detected in the outermost annuli, which suggests that the enrichment by both type Ia and core-collapse SNe started in the early stages of the cluster formation. However, the particularly high Ca/Fe ratio that we find in the core is not well reproduced by the standard SNe yield models. Finally, a 2-D map of Fe abundance confirm the existence of a denser, colder, and Fe-rich ridge south-west of the core, previously observed by Chandra. The origin of this asymmetry in the hot gas of the cluster core is still unclear, but it might be explained by a past intense ram-pressure stripping event near the central cD galaxy. |
| |
Name: Michilli, Daniele
Talk/Poster: Talk
Title: First Batch of Discoveries from the LOFAR High-Time-Resolution LOTAAS Survey
Abstract:
LOTAAS (LOfar Tied Array All-sky Survey) is an ongoing survey for pulsars and fast radio transients with LOFAR.
LOTAAS takes advantage of the unique characteristics of this radio telescope to investigate a still unexplored parameter space in time domain radio astronomy.
In fact, LOFAR permits to reach a sensitivity and time resolution that have never before been accessible at the lowest frequencies detectable from the Earth.
LOTAAS uses 222 simultaneous fields-of-view to cover large areas of the sky per pointing, at high sensitivity.
With a small fraction of the total survey already processed, the success of this approach is highlighted by the discovery of 15 new pulsars thus far (several of which are among the nearest and lowest luminosity pulsars known).
Among these pulsars, 2 belong to a relatively new class of intermittently emitting sources known as RRATs.
While the total amount of regular pulsars expected to be detected with the survey is about 200, the number of RRATs is unknown, and may teach us about the total Galactic population of radio-emitting neutron stars.
Also, the unique characteristics of the survey give the possibility to discovery more exotic sources, in particular the mysterious Fast Radio Bursts, which could have revolutionary applications in astrophysics. |
| |
Name: Mikhailov, Klim
Talk/Poster: Poster
Title: Is SXT 1H 1905+000 a millisecond pulsar now?
Abstract:
Recently, 3 stellar binaries have been discovered that switch from accretion-powered to rotation-powered state and vice versa. At the same time, binary sources referred to as soft X-ray transients (SXTs) are also known to be capable of switching states. Based so far only on X-ray studies, SXTs were determined to undergo transitions between bright X-ray outburst and low-luminous "quiescent" state. One of such transients, SXT 1H 1905+000, was found to possess a very low X-ray luminosity, similar to what all transitional sources have while being rotation-powered. This might in turn mean that we should also expect radio emission from this source. The presence of radio pulsations would not only reveal a new evolutionary link between two different kinds of transients, but also help us learn more about the conditions under which the transitions usually occur. We outline the results of two Arecibo observations (in 2006 and 2015, respectively) that were performed to find radio pulsations from the SXT 1H 1905+000. |
| |
Name: Moscibrodzka, Monika
Talk/Poster: Talk
Title: Particle accelerations and synchrotron emission from a relativistic jet.
Abstract:
The Galactic center and core of M87 galaxy are ideal laboratories for testing various theoretical models of the magnetized plasma flows onto compact objects. Our general relativistic magnetohydrodynamic simulations of gas falling onto a black hole predict dynamical and radiative properties of accretion flows and jets near a Kerr black hole. I will present a comparison of our models to radio and millimeter observations of the supermassive object in the core of M87 galaxy. I will discuss the prospects for detecting the silhouette of the black hole horizon in this source. |
| |
Name: NWO, and the PEPSci PhD students and postdocs
Talk/Poster: Poster
Title: Introducing PEPSci - The Planetary and ExoPlanetary Science Programme
Abstract:
The Dutch Planetary and ExoPlanetary Science programme (PEPSci) is an initiative of NWO and SRON to establish a coherent and integrated network on the interface of astronomy and earth sciences. The programme focuses on the characterisation of planetary processes both within our own solar system and on exoplanets. The addressed topics span the full range from observations and modelling of planetary formation, planetary structures, geology, and atmospheres to the investigation of chemical and biological processes that are linked to organic matter and life. Launched in 2013, it is now well underway. By means of two posters, we would like to introduce the PEPSci network and give an overview of the sort of research that is performed in the programme. The first poster explains the context, the aim of the PEPSci programme and describes the two themes. The second poster, made by the PhD students and postdocs active in the network, shows examples of PEPSci science.
Formally eight projects have been granted in PEPSci, but since the kick-off many more researchers working on related topics have participated at PEPSci meetings and joined the network. Feel free to contact us at pepsci@nwo.nl if you would like to join too! |
| |
Name: Oostrum, Leon
Talk/Poster: Poster
Title: The 2012 decline of the R Coronae Borealis star V854 Cen
Abstract:
R Coronae Borealis (RCB) stars are rare, hydrogen-deficient, carbon-rich supergiants that show irregular declines in brightness by up to 8 magnitudes. During a decline, the stellar photosphere is obscured and the circumstellar environment becomes detectable.
In May-June 2012 multiple optical-to-near-infrared spectra were obtained during a decline of V854 Cen with VLT/X-Shooter. A plethora of emission features is detected, mainly confined to the optical spectrum, including sharp lines of singly ionized metals such as Ti II, Sc II and Y II, and broad features of Ca II H and K, Na I D, H$\alpha$ and C I, spatially resolved along the X-Shooter slit. Furthermore, signatures of carbonaceous molecules are present: the C$_2$ (0-0) and (1-0) Swan bands, C$_2$ (3-0) Philips system and C$_3$ A-X (0-0). Most notably, a series of broad emission features appears off-source, with unknown carrier. Some of these unidentified features (UF) have been observed in the Red Rectangle proto-planetary nebula.
We report a new UF at 8692$\AA$ and confirm the presence of four of the seven previously detected UFs. We construct position-velocity diagrams of the emission line carriers in the nebula; the distribution of Na I D emission in the nebula is similar to that of Ca II H and K, showing predominantly high velocities up to 200 km/s. The H$\alpha$ emission seems to be asymmetrically distributed around the star, and does not show a preference towards higher velocities. The C$_2$ and C$_3$ bands are stronger on the side of the star where H$\alpha$ is weaker. The UFs follow the distribution of the carbon bands. Clearly, the physical and chemical conditions vary in the circumstellar (dust) cloud. The carriers of the UFs are most likely carbonaceous molecules. |
| |
Name: Ootes, Laura
Talk/Poster: Poster
Title: The accretion rate dependence of burst oscillation amplitude
Abstract:
Neutron stars in low mass X-ray binaries accrete matter from their companion via Roche-Lobe overflow. The accreted matter forms a layer on top of the solid crust of neutron star. Compression of this layer under its own gravity can lead to a thermonuclear instability, causing the accreted hydrogen-rich material to ignite into a type I X-ray burst. Part of the known type I X-ray burst sources exhibit burst oscillations in some of their bursts; signals with a frequency close to the spin frequency of the neutron star and a typical fractional rms amplitude of 0.10. With the discovery of burst oscillations by Strohmayer et al. (1996) it was suggested that they were likely to be caused by asymmetric brightness patterns on the burning surface. However, the underlying mechanism that causes the asymmetries is still unknown.
Muno et al. (2004) showed that the occurrence of burst oscillations is independent of the properties of the X-ray bursts themselves, and that they instead seem to occur preferentially at high accretion rates. They proposed that at lower accretion rates the burst oscillation amplitudes are attenuated. In this research the accretion rate dependence of burst oscillation amplitude is investigated for six known burst oscillation sources by analysis of archival RXTE data. We investigate the same sources as Muno et al. (2004), but analyse a significantly larger burst sample in order to determine whether the burst oscillation amplitude decreases gradually at lower accretion rates, or follows a step function. This relation can be used to constrain the mechanism causing the asymmetries on the burning surface of accreting neutron stars. Furthermore, two type I X-ray burst sources where oscillations have not yet been observed (4U 1705-44 and 4U 1746-37) are studied to constrain the upper limits on the oscillation amplitudes in these sources and to determine the reason for the absence of observed burst oscillations.
Our method of computing oscillation amplitudes for each burst is very similar to the one used by Muno et al. (2004), with a small difference in the definition of the timebins in which each burst is divided and a difference in the definition of amplitude upper limits. Furthermore, while Muno et al. (2004) only consider the rms amplitudes as function of accretion rate, we also consider the measured power from which those amplitudes are computed, as any trend that can be determined from the amplitude should be visible in the measured powers as well. We used the Sz value as a measure of accretion rate. This value is determined from the position of the source on its colour-colour diagram, in which the source describes a Z-shaped pattern as the accretion rate increases (Hasinger and van der Klis, 1989).
Comparing measured powers at different accretion rates revealed that at all accretion rates signals with a relatively low measured power can be found. On top of that, at high accretion rates (Sz > 1.7) about 28% of the bursts contain oscillation signals with a measured power up to 5 times larger than average. A similar trend can be found for the burst oscillation amplitudes as a function of accretion rate. At all accretion rates signals with low amplitudes (0.05 1.7 larger amplitudes are found as well. These results confirm that the burst oscillation amplitude decreases at lower accretion rates, as suggested by the data from Muno et al. (2004). Analysis of the data over all frequencies that can be supported by neutron star EOSs (0-2048 Hz) indicates that the small number of bursts observed at high accretion states (Sz > 1.7) of sources 4U 1705-44 and 4U 1746-37 is sufficient to explain the lack of observed burst oscillations in these sources. These sources are therefore not anomalous in their behaviour. |
| |
Name: Orru, Emanuela
Talk/Poster: Talk
Title: LOFAR results on a famous double-double radio galaxy
Abstract:
In the last decade the understanding of the AGN-galaxy feedback mechanism became one of the main focus in many fields of astrophysics.
Observations of AGNs at low radio frequencies allow us to investigate on the current and past jets activity and their effects on the ISM, IGM and ICM.
I will present the results obtained including LOFAR observations in the spectral studies of a famous AGN which shows evidence of jet intermittency: the double-double radio galaxy B1834+620. The detection of significant polarized emission will be also discussed. |
| |
Name: Patruno, Alessandro
Talk/Poster: Talk
Title: The Reflares and Outburst Evolution in the Accreting Millisecond Pulsa r SAX J1808.4--3658
Abstract:
The accreting millisecond X-ray pulsar SAX J1808.4--3658 shows peculiar low luminosity states known as ``reflares'' after the end of the main outburst. During this phase the X-ray luminosity of the source varies by up to three orders of magnitude in less than 1--2 days. The lowest X-ray luminosity observed reaches a value of 1e32 erg/s, only a factor of few brighter than its typical quiescent level. We investigate the 2008 and 2005 reflaring state of SAX J1808.4--3658 to determine whether there is any evidence for a change in the accretion flow with respect to the main outburst. I present results of a multiwavelength photometric and spectral study of the 2005 and 2008 reflares with data collected during an observational campaign covering the near-infrared, optical, ultra-violet and X-ray band. We find that the NIR/optical/UV emission, expected to come from the outer accretion disk shows variations in luminosity which are 1--2 orders of magnitude shallower than in X-rays. The spectral state observed during the reflares does not change substantially with X-ray luminosity indicating a rather stable configuration of the accretion flow. We investigate the most likely configuration of the innermost regions of the accretion flow and we infer an accretion disk truncated at or near the co-rotation radius. We interpret these findings as due to either a strong outflow (due to
a propeller effect) or a trapped disk (with limited/no outflow) in the inner regions of the accretion flow. |
| |
Name: Pijloo, Janatie
Talk/Poster: Talk
Title: The EGAPS Open Cluster Catalogue
Abstract:
With data from the European Galactic Plane Surveys (IPHAS, UVEX and VPHAS+) we aim to construct a homogeneous open cluster catalogue. |
| |
Name: Podigachoski, Pece
Talk/Poster: Talk
Title: Star formation in z > 1 3CR host galaxies as seen by Herschel
Abstract:
Massive galaxies formed rapidly in the early universe. Scaling relations imply that their massive black holes (BH) also formed rapidly. Active massive galaxies are thus ideal objects to probe for coeval BH and host galaxy growth, particularly at the epoch when both processes went through their peak activity (z ~ 2). Using our Herschel, and other multiwavelength supplementary data, we study the full infrared (IR) spectral energy distributions of a complete sample of objects - the hosts of the 3CR radio sources with z > 1. We separate the respective BH and star formation (SF) activity contributions to their total IR luminosities, and obtain various physical properties for the hosts of these powerful active galactic nuclei (AGN). Despite the strong AGN activity, we find prodigious SF activity in many of these objects, with typical SF rates of hundreds of solar masses per year. The high levels of star formation are particularly found in the hosts of the smaller radio sources, suggesting occurrence of jet-induced star formation (positive feedback). We show that radio galaxies and quasars have different mid-infrared, but indistinguishable far-infrared colors, entirely in line with expectations from the unification model for radio-loud AGN. |
| |
Name: Portegies Zwart, Simon
Talk/Poster: Talk
Title: Simulating a disk galaxy on a star-by-star basis
Abstract:
For our Gordon Bell Prize nomination we have simulated the Milky Way Galaxy using up to 242 billion particles. The number of stars in our simulation is comparable to the number of stars in the Galaxy. The calculations are performed on two supercomputers: Piz Daint at the Swiss National Supercomputing Centre and Titan at Oak Ridge National Laboratory. On the latter machine we achieve a sustained performance of 24.77 PFlops on 18600GPUs. During our simulation Our simulations for bar and spiral structure not incomparable to the structure observed in the Milky Way. We intend to compare our simulation results directly with the billion stars for which Gaia will in 2017 deliver astrometric parameters. We will give an overview of the algorithms used to achieve the measured speed and review what this will tell us about the Milky Way galaxy.
|
| |
Name: Ramatsoku, Mpati
Talk/Poster: Poster
Title: A blind HI-imaging of an obscured Perseus-Pisces Filament
Abstract:
Based on the systematic HI follow-up survey of 2MASS bright galaxies in the Zone of Avoidance (ZOA) with the Nançay Radio Telescope (NRT), we discovered a prominent filament crossing the Galactic Plane at longitudes of ≈ 160° (Ramatsoku et al. 2014, Kraan-Korteweg in prep). The filament seems to form part of the Perseus-Pisces Supercluster (PPS) and may well be part of the often hypothesized connection of the PPS to Lynx.
Right within this HI-galaxy filament we note a high concentration of 2MASX sources which (a) coincide with the position of an X-ray cluster CIZA J0450.0+4501 (Ebeling et al. 2002) discovered in their search for X-ray clusters in the ZOA and (b) hosts two strong radio galaxies 3C129 and 3C129.1 discovered much earlier by Spinrad (1975). All of these observations point to the existence of yet another nearby rich cluster which has remained elusive due to its location behind a dust layer of AB ≈ 4.5 mag at its position of (l,b) ≈ (160°, 0.5°) and which is a further constituent of the PPS. As such it will contribute to the local density, and influence the local flow fields.
Here we present first results from a blind HI imaging survey of about 2.4 x 2.4 degrees mosaic pursued with the Westerbork Synthesis Radio Telescope (WSRT) to learn more about this obscured cluster, its surroundings and its effect on the local flow field. |
| |
Name: Ramirez Agudelo, Oscar Hernan
Talk/Poster: Talk
Title: On the stellar and wind properties of massive stars in 30 Doradus
Abstract:
Massive stars, with initial masses than 10 solar masses, are powerful cosmic engines that strongly impact their immediate surroundings. Stellar winds and rotation are key parameters in their evolution, affecting the evolution, chemical yields, ionizing photon budget, and the final fate as supernovae and long-duration gamma-ray burst.
Models of their evolution predict the series of morphological states that massive stars pass through before reaching their final fate, therefore studying populations of massive stars is a proven way of testing the outcome of such calculations. In this way, O-type stars are of particular interest as they sample the main sequence phase in the range of 15 Msun to ~100 Msun, be they dwarfs, giants or supergiants.
We, the VLT-FLAMES Tarantula Survey (VFTS), have obtained multi-epoch optical spectroscopy of over 300 O-type objects in the 30 Doradus (30 Dor) region. It contains the richest population of massive stars in the Local Group and is the best possible laboratory to investigate open questions on the formation and evolution of massive stars.
Here we will present the results of the atmospheric analysis of ~100 spectroscopic-single O-type stars in the VFTS. We constrain the stellar and wind parameters by combining the non-LTE stellar atmosphere model FASTWIND with a generic fitting algorithm approach.
By confronting the stellar characteristics with evolutionary tracks for single stars we established the evolutionary state, age, and mass. As a result, we argue that some of our sample stars might be post-interaction systems or even merged stars. Finally, the wind-strength of our stars is higher than theoretical predictions. This may be interpreted as an effect of the wind being clumped. |
| |
Name: Rapisarda, Stefano
Talk/Poster: Talk
Title: Testing propagating mass accretion rate fluctuations model PROPFLUC on Black Hole X-ray Binaries
Abstract:
Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of black hole X-ray binaries. However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and a quasi-periodic oscillation (QPO) on the precession frequency. We recently applied systematically for the first time PROPFLUC on a black hole candidate (MAXI J1543-564) in order to compare the results of phenomenological and physical modelling of the source power spectrum and to give a physical interpretation of the rising phase of the source outburst. I will present the results of this study and describe our work to go beyond power spectral fitting by also modelling the cross-spectral amplitudes and phase lags between different energy bands. We are testing the model by comparing with Swift data from the black hole binary MAXI J1659-152. In particular, we are exploiting the low energy coverage of Swift in order to test the hypothesis that fluctuations are generated in the disc before propagating into the inner flow. This is the first study to utilise quantitive fitting of a physical model simultaneously to observed power and cross-spectra. |
| |
Name: Ribeiro, Valerio
Talk/Poster: Talk
Title: Some things Novae
Abstract:
The nova eruption is the most common thermonuclear explosion in our Galaxy, occurring on the surface of a white dwarf star. The nova eruptions are now bona fide multi-frequency objects, from gamma-rays to radio-waves. I will describe recent efforts to understand these explosions from the theoretical and observational prospective at radio and optical wavelengths and where we will be in the next few years leading up to the SKA. In particular, I will discuss our efforts to understand the amount of ejected mass in order to determine if the white dwarf is growing or not in mass. |
| |
Name: Ripperda, Bart
Talk/Poster: Talk
Title: Particle acceleration due to interacting tilt and kink instabilities in repelling current channels
Abstract:
Particle acceleration due to interacting tilt and kink instabilities in repelling current channels
B. Ripperda, R. Keppens
Centre for mathematical Plasma-Astrophysics, Department of Mathematics, KU Leuven
We present a numerical study where we use a combination of resistive magnetohydrodynamic (MHD) and test-particle methods to analyze particle acceleration in two repelling current channels. The initial MHD equilibrium configuration contains adjacent, oppositely directed, parallel current channels, which consequently repel each other. The equilibrium is sensitive to an ideal magnetohydrodynamic tilt instability in the plane. This leads to the creation of (near) singular current sheets which in turn can accelerate particles. Our aim is to investigate how efficiently reconnection accelerates charged particles and what kind of energy distribution they acquire.
In a three-dimensional setup, both current channels can be liable to an additional kink instability (Keppens et al. 2014). The effects of having both tilt and kink instabilities on particle acceleration in the violent, reconnection-dominated evolution are discussed.
With our open-source grid-adaptive MPI-AMRVAC software (Porth et al. 2014) we revisit the 3D resistive MHD evolution of the tilt-kink instability for several realistic equilibriums which then yield as background fields for a recently implemented test-particle module based on a guiding centre approximation. We also analyze when the guiding-centre approximation is valid in an astrophysical environment.
As a concrete astrophysical application, it is argued that interacting tilt-kink instabilities in repelling current channels provide a novel route to initiate particle acceleration in solar coronal mass ejections.
REFERENCES
Keppens, R., Porth, O., & Xia, C. 2014, ApJ, 795, 77
Porth, O., Xia, C., Hendrix, T., Moschou, S.P., & Keppens, R. 2014, ApJS, 214, 4
|
| |
Name: Rivera, Liliana
Talk/Poster: Talk
Title: Compact Binaries in the Globular Cluster 47 Tucanae
Abstract:
Globular clusters (GCs) are excellent laboratories for studying compact binaries because of the high stellar densities that can be reached in the cores. We present results of a near-ultraviolet (NUV) study of close binaries in the GC 47 Tucanae, for which we obtained Wide Field Camera 3 images with the Hubble Space Telescope (HST). In combination with existing deep optical HST and Chandra X-ray data, we identify compact binaries, particularly faint cataclysmic variables (accreting white dwarfs). Our aim is to understand the effects of dynamical interactions on compact binaries, by comparing our results to other globular clusters and to the galactic field results. We present the discovery of two millisecond pulsar companions in our data set and we discuss those systems in the context of binary evolution in globulars. |
| |
Name: Rodenhuis, Michiel
Talk/Poster: Talk
Title: NOVA: A leading partner in E-ELT instrumentation
Abstract:
Continuous improvement in instrumentation is essential when conducting research at the forefront of astronomy. NOVA, including its optical-infrared instrumentation group in Dwingeloo, has strived to be a key partner in many if not most of the major ESO-led instrument projects over the past decade. The start of E-ELT construction provides a new impetus to this quest.
The E-ELT represents an enormous leap in the capabilities of astronomical instrumentation, enabling ground-breaking results, from unraveling the nature of Dark Energy to characterizing extra-solar planets, from resolved studies of stellar populations outside our local group to the formation and evolution of galaxies in the early universe.
This contribution provides an overview of the E-ELT instrumentation projects that NOVA is involved in: METIS, the Mid-infrared E-ELT Imager and Spectrograph, MOSAIC, the Multi-Object Spectrograph, MICADO, the Multi-AO Imaging Camera for Deep Observations and EPICS, the Exoplanet Imaging Camera and Spectrograph. I will focus on the R&D efforts NOVA has undertaken to be able to play a leading or major role in these projects. This includes the development of immersed grating technology, high-contrast polarimetric integral field spectroscopy, novel coronagraph concepts and focal-plane wavefront sensing for extreme AO.
|
| |
Name: Roelofs, Freek
Talk/Poster: Poster
Title: Observing time-variable black holes with the Even Horizon Telescope
Abstract:
The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array aiming to image Sagittarius A* (Sgr A*), the radio source associated with the supermassive black hole at the center of the Milky Way, on event horizon scales. General relativistic magnetohydrodynamic (GRMHD) simulations show that radio emission from Sgr A* exhibits variability on timescales of minutes, whereas VLBI observations typically take several hours. One of the key assumptions needed for radio interferometry to theoretically work is that the source does not change during the observations. According to recent models, this condition is clearly violated for Sgr A*. In this research project, simulated EHT observations of a model movie of Sgr A* have shown that an image of the average quiescent emission, featuring the characteristic black hole shadow and photon ring predicted by general relativity, can nonetheless be obtained by averaging visibilities over multiple nights, scaling them by the instantaneous zero-spacing flux density, and applying a smoothing algorithm before imaging. Also, it has been shown that this procedure can be combined with an existing method to mitigate the effects of interstellar scattering on the reconstructed image. |
| |
Name: Saladino Rosas, Martha Irene
Talk/Poster: Poster
Title: Mass transfer in binary stars
Abstract:
Most stars are found in binary systems and in many cases they are close enough that mass transfer can occur. This outflow of matter can happen via different scenarios and may affect the evolution of the system. We want to investigate the theory of mass transfer in eccentric low-mass binaries to see how the mass accreted by the companion depends on the orbital parameters of the system, to study the structure of the material leaving the star, and to determine its effect on the evolution of the orbit. In order to do so, we are performing numerical simulations of the phenomenon using the Astrophysical Multipurpose Software Environment (AMUSE) which combines hydrodynamics, stellar evolution and gravitational dynamics. |
| |
Name: Santoro, Francesco
Talk/Poster: Talk
Title: The Outer Filament of Centaurus A as seen by MUSE
Abstract:
Radio-loud active galactic nuclei (AGN) are known to inject kinetic energy into the surrounding interstellar medium (ISM) of their host galaxy via plasma jets. How the interaction between the jet and the ISM proceeds, how it depends on the kinetic power of the jet, and whether this process is relevant in the more common low-power radio
galaxies, are still debated questions.
Centaurus A is a relatively low-power radio galaxy as well as the nearest AGN. This makes Cen A an excellent laboratory in which the detailed physics of the coupling of jet mechanical energy to the surrounding medium may be investigated.
About 15 kpc northeast of this galaxy, a particularly interesting region is found: the so-called outer filament, where a complex interplay between radio plasma and ionized and neutral gas has been proposed to occur.
We will present optical integral field observations of the outer filament obtained using MUSE, recently installed on the VLT. With a spatial resolution that reaches pc scales, the new observations reveal with exquisite detail the complex kinematics of the ionized gas at this location together with its intriguing variety of morphological
structures.
Looking at the kinematics we are able to identify three main components that interestingly show different morphologies. One of them appears to be collimated along the direction of the radio jet and is likely shaped by its lateral expansion. Moreover, a number of peculiar arc-like structures oriented along the jet direction are found within the other two components. These features are the clearest evidence that a smooth jet-ISM interaction is occurring also along the jet direction.
For each gas component we will discuss the constraints on gas temperature and density coming from the analysis of the [OI], [NII] and [SII] lines; and, in order to disentangle the dominant ionization mechanism, different ionization models (i.e. photoionization and shock models) will be also compared to the extracted line ratios within diagnostic diagrams.
Our results show that despite the jet of Cen A is a low-power jet, the effects of its lateral and head-on interaction with the surrounding ISM are clearly visible.
The study we present has many important implications for the AGN feedback process in general because this is the first time that the ionized gas and its kinematics can be traced at the location of a jet-cloud interaction on pc scales. |
| |
Name: Saxena, Aayush
Talk/Poster: Poster
Title: Estimating number counts of steep-spectrum radio sources at high redshifts
Abstract:
Very little is known about the luminosity function of steep-spectrum radio sources beyond redshift 2. This is due to a dearth of source counts at high redshifts. LOFAR, with its unparalleled sensitivity at low radio frequencies, will observe numerous high redshift steep spectrum radio galaxies. To maximise the number of sources observed in a LOFAR survey, a compromise must be achieved between the coverage area on the sky (number of pointings) and the noise level (integration time). In this poster, I will present a luminosity dependent density evolution (LDDE) model for the radio luminosity function (RLF) at z > 2 derived by convolving the evolution of radio galaxies with the evolution of optically selected quasars (which is much better constrained at high-z). This will enable the prediction of LOFAR observable radio galaxy counts at high redshifts, depending on the coverage area and the noise level achievable. Source count predictions will help plan and optimise current LOFAR surveys. With future observations, the free parameters in the model can be constrained and the evolution of radio galaxies over cosmic time can be studied. |
| |
Name: Schootemeijer, Abel
Talk/Poster: Poster
Title: The naked helium star in the binary φ Persei – clue to missing type Ib/c supernovae progenitors?
Abstract:
The system φ Persei consists of a very rapidly rotating Be star (M = 9.6 ± 0.3 Mʘ) and a hot stripped helium star (M = 1.2 ± 0.2 Mʘ) with a 126 day orbital period. The stripped helium star is thought to be the initially more massive star, which has transferred its hydrogen envelope to the secondary star by Roche-lobe overflow after its main sequence lifetime. This left the system as a stripped He core with a spun-up main sequence star. With observing campaigns by e.g. Gies et al. (1998) and Mourard et al. (2015), the full orbital solution of the system has been obtained.
In this research, the fast population synthesis code BINARY_C (see Izzard, 2009, and references therein) is used to derive the birth parameters of this system. A bayesian test of the simulated population using the observed parameters suggests that it is most probable that the system started with a 6 Mʘ primary, a 5 Mʘ secondary and an initial period of 7 days.
Interestingly, by far the best fits of the simulations to the observed parameters are when the He star in the He-shell burning phase. In this short-lived phase, which is around 20 to 30 times shorter than the He-core burning phase, the stripped He star becomes larger and more luminous. In other words, for every observed system similar to φ Persei, we expect 20 to 30 Be stars to be present which have a faint, very hard to detect naked He star companion.
While these unseen naked He stars do not contribute much light in the optical, they emit most of their light in the UV and are therefore potentially important sources of ionising radiation. This system also provides insight in why we have not detected any of its higher mass counter parts, which are thought to be the missing progenitors of type Ibc supernovae. |
| |
Name: Schwarz, Henriette
Talk/Poster: Talk
Title: Spin measurement of the directly imaged extrasolar planet, GQ Lupi b
Abstract:
Recently we measured for the first time the spin rotation of an extra-solar planet. The famous planet beta Pictoris b was found to spin much faster than any planet in our solar system, which is in line with the idea that massive planets spin more rapidly. Interestingly, field brown dwarfs do not seem to follow this relation, which may indicate that an object's spin is closely linked to its formation mechanism.
Here I present the second spin measurement of an extrasolar planet, GQ Lupi b. The young T-Tauri system was observed for an hour with the CRIRES instrument at the VLT with a spectral resolving power of 100000, positioning the slit to both contain the host star and the companion separated from the host by 0.7 arcseconds. We have identified both CO and H2O in the planetary spectrum. |
| |
Name: Shulevski, Aleksandar
Talk/Poster: Poster
Title: A low frequency look of two giant radio galaxies
Abstract:
We present our 150 MHz LOFAR observations of NGC 6251 and 3C 236, exploring the morphological and spectral properties of these giant radio galaxies at the highest spatial resolution so far at these low frequencies. We report a discovery of a counter-jet in NGC 6251 and spectral steepening in the inner regions of the lobes of 3C 236. |
| |
Name: Smits, Roy
Talk/Poster: Talk
Title: ARTS: A new radio transient system at the WSRT
Abstract:
The Westerbork Synthesis Radio Telescope (WSRT) is an array of 14 25-meter dishes spread over an East-West baseline of 2.7 kilometers. For the past 45 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 FoV makes the telescope also sensitive to detecting rare radio bursts, such as RRATS (Rotating RAdio Transients) and FRB's (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. |
| |
Name: Tolstoy, Eline
Talk/Poster: Talk
Title: MICADO – first light near-infrared imaging and spectroscopy at the E-ELT
Abstract:
MICADO is the Multi-AO Imaging Camera for Deep Observations that will work with adaptive optics on the 39-m European Extremely Large Telescope. It will provide the E-ELT with a first light capability for diffraction limited imaging and wide wavelength range spectroscopy at near-infrared wavelengths. The instrument is optimized to work with a ~1arcmin field corrected by the laser guide star multi-conjugate adaptive optics module MAORY. It also includes a natural guide star wave-front sensor for single-conjugate adaptive optics. The key capabilities of MICADO exploit the most unique features of the E-ELT: sensitivity and resolution.
The Netherlands, through NOVA, is a key partner in the international consortium that is going to build MICADO. We will be responsible for several key components in the instrument, including the Atmospheric Dispersion Corrector and the Data Flow system.
I will describe the status of this project that will kick-off in September or October this year, and also give an overview of the scientific drivers that have motivated the development of this instrument. I will also outline the Dutch role in this project and the future prospects for Dutch astronomers to be more involved. |
| |
Name: Uttley, Phil
Talk/Poster: Talk
Title: Why X-rays from black holes vary: the role of the accretion disc
Abstract:
X-ray variability from black holes has been studied for many years, but we have only recently pieced together the physical origin of the variability. Developments in X-ray spectral-timing now allow us to study the causal relationship between variations of different spectral components, allowing a direct link to the physics of the emitting regions close to the black hole. In particular, it has become apparent that the `standard' blackbody-emitting accretion disc plays a much bigger role in generating the variations than previously thought, possibly through the same magnetorotational turbulence that provides the disc's viscosity. I will describe some recent advances in this area which reveal some surprises about the role of the turbulent accretion disc in producing not only the variability, but possibly also the power-law emitting `corona' component too. |
| |
Name: van Bemmel, Ilse
Talk/Poster: Poster
Title: BlackHoleCam activities in JIVE
Abstract:
As a partner in the BlackHoleCam project, JIVE is leading two workpackages. The first deals with upgrading the CASA software to a full VLBI capable package, and develop a pipeline for high-frequency VLBI. The second workpackage focuses on simulations of the telescope, to study instrumental and atmospheric effects, as well as test the newly developed software.
I will discuss the status of the work in JIVE and the context of how this fits in the BlackHoleCam project.
|
| |
Name: van der Helm, Edwin
Talk/Poster: Talk
Title: Creating Arches
Abstract:
I use AMUSE to simulate an embedded star cluster in a tidal potential, including stellar evolution and feedback, to investigate the creation and evolution of the Arches cluster near the Galactic center.
This talk would be very suitable for the "Supercomputing in Astronomy" session. |
| |
Name: van der Hulst, Thijs
Talk/Poster: Talk
Title: Big Data Challenges for Future HI surveys
Abstract:
The next decade will feature several major HI sky surveys, each producing a total of several Peta Bytes of data. A major challenge is to automate not only the data processing but also the extraction of useful astronomical information about the objects in the data. The scientific legacy value of the survey data will depend on how robust and quantitative the extracted information is. Development of the appropriate techniques needs expertise in several fields: observational astronomy, computer science and visualisation. Purpose of this presentation is to demonstrate the challenges using existing HI experience coupled to new developments in computer science and to describe current developments at the Kapteyn Institute geared towards preparing for HI surveys with APERTIF on the WSRT. |
| |
Name: van der Marel, Nienke
Talk/Poster: Talk
Title: Mind the gap: gas and dust in planet forming disks with ALMA
Abstract:
Protoplanetary disks with large dust cavities around young stars (also called transition disks) form an excellent laboratory to study planet formation and disk evolution. In recent years, ALMA observations of transitional disks of the continuum emission (originating from the millimeter-sized dust) have revealed ring-like structures, sometimes with azimuthal asymmetries. These structures have been suggested to have their origin in dust traps, caused by pressure bumps in the gas. One of the ways to generate such a bump is by the presence of one or more recently formed planets, which lower the gas density along their orbit and create a pressure bump at the edge. The drop in gas density inside the cavity depends on the mass of the companion and the viscosity of the disk. Also, the gas cavity radius is expected to be smaller than the dust cavity radius. I present spatially resolved ALMA Band 7 and Band 9 observations of CO and CO isotopologues of several famous transitional disks with spatially resolved cavities. The dust and gas emission are analyzed using the physical-chemical modeling tool DALI in order to constrain the gas and dust density inside the cavity. The majority of these disks indeed reveal gas cavities that are smaller and with shallower depth than the dust cavities. I will discuss the implications for these disks and the prospects of young embedded planets. The high spatial resolution and sensitivity of ALMA give a unique opportunity to look into the earliest phases of planet formation. |
| |
Name: Vandenbroucke, Bert
Talk/Poster: Talk
Title: Advanced methods in Nbody/hydrodynamical simulations
Abstract:
In 2007, Agertz et al. showed that standard Lagrangian particle-based hydrodynamical solvers and in particular Smoothed Particle Hydrodynamics (SPH) are unable to resolve some physical features of astronomical fluids due to numerical problems with the method. Since then, a whole new class of hydrodynamical solvers has been developed to overcome these problems. Some of these methods introduce artificial correction terms to the equations of SPH to suppress the numerical effects that cause the method to fail.
Another, more drastic method to solve the problems with SPH is to abandon the idea of using particles altogether and to consider a Lagrangian grid instead. Since their introduction for astrophysical purposes, these moving mesh methods have grown in importance and have illustrated their usefulness, e.g. for the Illustris simulation.
Shadowfax is a moving mesh hydrodynamical N-body simulation code that is currently being developed at Ghent University. It can be used to solve hydrodynamical problems in two and three dimensions, including problems with self-gravity. The code is parallelized for use on distributed memory systems and has been tested on a variety of hydrodynamical test problems up to reasonable problem sizes (10^6 cells).
During my talk, I will first introduce the moving mesh method in some more detail and illustrate its validity using results obtained with Shadowfax. I will then discuss the differences between the moving mesh method and other methods, e.g. SPH and Adaptive Mesh Refinement (AMR), focussing on the advantages of the method and the computational issues that arise.
I will also compare the moving mesh technique with the mesh-free hydrodynamical methods introduced by Hopkins (2014), using some of the first results obtained using the GIZMO module of the hydrodynamical simulation code SWIFT, which is currently being developed in collaboration with the Institute for Computational Cosmology in Durham. |
| |
Name: Verbeke, Robbert
Talk/Poster: Poster
Title: First stars shaping faint, gas-rich dwarfs and the origin of the baryonic Tully-Fischer relation
Abstract:
In the ΛCDM cosmological model, cosmic structure forms in a hierarchical fashion. According to this paradigm, even low-mass dwarf galaxies grow via smooth accretion and mergers. Given the low masses of dwarf galaxies and their even smaller progenitors, the cosmic UV background, responsible for reionizing the Universe by redshift z~6, is expected to have a significant influence on their gas content and, consequently, on their star formation histories. Generally, cosmological simulations predict that most dwarf systems with circular velocities below ~30 km/s should not be able to form significant amounts of stars or contain gas and be, in effect, "dark" galaxies (Sawala et al. 2013, 2014; Hopkins et al. 2014; Shen et al. 2014). This is in apparent contradiction with the recent discovery of very low-mass yet gas-rich dwarf galaxies, such as Leo P (Skillman et al. 2013), Pisces A (Tollerud et al. 2014), and SECCO 1 (Bellazzini et al. 2015).
Moreover, Tollerud et al. (2014) make the very intriguing point that the ELVIS suite of Local Group simulutions predicts that there should be one to three dwarf halos inside the observation box of the GALFA-HI survey during which Pisces A was discovered. This is a very profound result: the fact that the number density of HI-detected faint dwarfs roughly equals that of corresponding dark-matter halos indicates that most isolated dark-matter halos down to circular velocities of ~15 km/s contain neutral gas, in direct contradiction with the predictions of current simulations.
Based on a suite of simulations of the formation and evolution of dwarf galaxies we show that, if the strength of the first peak of star formation can be sufficiently reduced, e.g. by including feedback from population III stars in the simulations, the resulting dwarf galaxies have severely suppressed star-formation rates while holding on to their gas reservoirs. Moreover, we show that the majority of the zero-metallicity stars are ejected during merger events so that there is a marked difference between a galaxy's "real" star-formation history and the one read from the stars that are still present inside the galaxy at z=0. This mechanism leads to the formation of realistic low-mass, gas-rich dwarfs with a broad range of star formation histories (from early stellar mass assembly to delayed star-formation) and which adhere to the observed scaling relations, such as the baryonic Tully-Fisher relation.
In short, the simulations presented here are for the first time able to reproduce the observed properties of the newly discovered low-mass, gas-rich dwarfs such as DDO 210, Leo P and
Pisces A. |
| |
Name: Verdoes Kleijn, Gijs
Talk/Poster: Talk
Title: Treasure trove OmegaCAM for the Dutch community
Abstract:
The Dutch-led OmegaCAM wide-field imager is a workhorse for a wide range of science projects. It includes Galactic stellar streams, weak-lensing, strong-lensing, compact binaries, dwarf galaxies, galaxy evolution and high redshift quasars. The projects range from a few nights worth of data up to projects of several hundred nights. In this talk I present recent science highlights. In view of the wealth of public science-ready data and the remaining Dutch Guaranteed Time I conclude with an overview of the tools and infrastructure available to Dutch astronomers to exploit it.
|
| |
Name: Vink, Jacco
Talk/Poster: Talk
Title: The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud
Abstract:
The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known, N 157B; the radio-loud supernova remnant N 132D; and the largest nonthermal x-ray shell, the superbubble 30 Dor C. The unique object SN 1987A is, unexpectedly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a g-ray source population in an external galaxy and provide via 30 Dor C the unambiguous detection of g-ray emission from a superbubble. |
| |
Name: Wang, Yanan
Talk/Poster: Poster
Title: Modelling the X-ray spectra of the black hole candidate 4U 1630-47 during its 2012 outburst
Abstract:
Diaz Trigo et al. (2013) reported the detection of three relativistically Doppler-shifted emission lines arising from baryonic matter in a jet of 4U 1630-47 during its 2012 outburst.
Here we proposed an alternative model to fit the same data with Diaz Trigo et al. (2013) and found the model fits the data well without the need of Doppler-shifted lines from the jet.
But the abundances of S and Fe along the light of sight differed from their solar values.
Except that, we also used this alternative model to fit all the six XMM-Newton observations simultaneously and added some Gaussian absorption lines and edges. These absorption lines of Fe XXV, Fe XXVI,Ni XXVIII and edges of Fe XXV, Fe XXVI indicate that there is a local absorber which is highly ionized. |
| |
Name: Wijers, Ralph
Talk/Poster: Talk
Title: Forbidden transients?
Abstract:
There are solid physical arguments why radio transients at low frequency should be faint, or slow, or both. Some recent papers make this case clearly. And yet, the slight peaks we have as yet been able to make into this supposedly empty parameter space do reveal new, exciting, classes of radio transient that violate said prohibitions. What are they? What physics allows them to violate the naive constraints that some have imposed on them? And what lies ahead, lurking in the shadows of time domain astronomy? |
| |
Name: Wijnen, Thomas
Talk/Poster: Talk
Title: Accretion onto Protoplanetary Discs
Abstract:
In the past decade, observational evidence that Globular Clusters (GCs) harbour multiple stellar populations has grown steadily. These observations are hard to reconcile with the classic picture of star formation in GCs, which approximates them as a single generation of stars. However, Bastian et al. recently suggested an evolutionary scenario in which a second (and higher order) population is formed by the accretion of chemically enriched material onto the low-mass stars in the initial GC population. In this early disc accretion scenario the low-mass, pre-main sequence stars sweep up gas expelled by the more massive stars of the same generation into their protoplanetary disc as they move through the cluster centre. Using assumptions that represent the (dynamical) conditions in a typical GC, we investigate whether a low-mass star surrounded by a protoplanetary disc can indeed accrete sufficient enriched material to account for the observed abundances in 'second generation' stars. We compare the outcome of two different smoothed particle hydrodynamics codes and check for consistency. In particular, we focus on the lifetime and stability of the disc and on the gas accretion rate onto both the star and the disc. |
| |
Name: Yoon, Ilsang
Talk/Poster: Talk
Title: Bound isothermal sphere reloaded: Implication to the distribution of intracluster medium
Abstract:
When a self-gravitating isothermal sphere is embedded in a deep potential well, the potential well becomes a thermodynamical heat bath and the em- bedded sphere reaches a quasi-thermal equilibrium with the potential well accompanied by increasing velocity dispersion. Therefore, a self-gravitating sphere embedded in a dark matter halo potential well has a large kinetic energy and is not bound by its own gravity but by the potential well. In this talk, I will introduce such bound isothermal sphere as a model of the density distribution of intracluster gas in galaxy cluster. I compute the equilibrium density profiles of bound isothermal sphere within dark matter potential wells by solving Jeans equation and Poisson equation including self-gravity and velocity anisotropy and model the radial density distribution of intracluster gas in galaxy clusters. The density profile of the bound isothermal sphere matches the observation and provides the parameters of the surrounding dark matter potential well. The models are physically motivated and can be used for testing dark matter potential models by comparing to the density profiles of intracluster gas measured by X-ray observation. |
| |
Name: Zapartas, Manos
Talk/Poster: Talk
Title: The impact of binarity of massive stars on the delay time distribution of core-collapse supernovae
Abstract:
Authors: E. Zapartas, S.E. de Mink, R.G. Izzard, A. de Koter, C. Badenes, S.-C. Yoon
Core-collapse supernovae (ccSNe) mark the end of the lives of massive stars. The majority of these massive stars experience interaction with a binary companion before they explode. We use a population synthesis approach to investigate the delay-time distribution and the production of hydrogen-rich (type II) and stripped (type Ib/c) ccSNe.
We find up to 30% more ccSNe in a realistic population with massive binary stars compared to a pure single star population of the same total mass. Interestingly, we find that 10-25% of all ccSNe are “lateâ€, i.e. they occur 50-200 Myrs after birth, when all single stars have already died. These late ccSNe originate from intermediate mass stars that gained mass from a binary companion. An observational signature of this late channel seems present in the delay time distribution inferred from supernova remnants in the Magellanic Clouds.
We find that the large majority of ccSNe originate from stars that have experienced binary interaction in the past, severely altering their properties. Our results will be very relevant for future comparison with the results from all-sky automatedtransient surveys and as improved input models for stellar feedback in cosmological and galaxy formation simulations. |
| |
Name: Zari, Eleonora
Talk/Poster: Poster
Title: Herschel-Planck dust optical depth and column density maps
Abstract:
We present optical depth and temperature maps of the Perseus molecular cloud, obtained combining dust emission data from the emph{Herschel} and emph{Planck} satellites and 2MASS/NIR dust extinction maps. The maps have a resolution of 36~arcsec in the emph{Herschel} regions and of 5~arcmin elsewhere. The dynamic range of the maps goes from $1times10^{-2}, mathrm{mag}$ to $20 ,mathrm{mag}$ in $K$ extinction band. We also evaluate the ratio between the $2.2 mathrm{mu m}$ extinction coefficient and the $850 mathrm{mu m}$ opacity. The value we obtain is close to the one found in the Orion molecular cloud. We show that the cumulative and the differential area function of the data (which is proportional to the probability distribution function of the cloud column density) follow power laws with index respectively $simeq -2$, and $simeq -3$. Besides, we use WISE data to upgrade pre-existing YSO catalogs based mostly on emph{Spitzer} data and we build an up-to-date selection of Class~I/0 objects. Using this selection, we evaluate the local Schmidt law, $Sigma_{mathrm{YSO}} propto Sigma_{mathrm{gas}}^{beta}$, showing that $beta simeq 2$ and confirming the trend observed for other molecular clouds. |
| |
