Seminars 2017
13.11.2017 14:00
Robert Williams
Space Telescope Science Institute, Baltimore
The Hubble Deep Field and its Legacy
Abstract
Robert Williams
The Hubble Deep Field and its Legacy
The history of how and why the original Hubble Deep Field was undertaken will be described, including the features that made it unique. The characteristics of subsequent HST deep fields will be explained, including how they helped lead to the discoveries of dark energy, the distribution of dark matter, and the rate of star formation since the Big Bang. The results of all the deep fields combined with recent detailed numerical simulations from supercomputers have now produced a realistic model for galaxy formation and evolution over cosmic time.
01.11.2017 14:00
Sarah Jaffa
Cardiff University, UK
Reading patterns in the sky
Abstract
Sarah Jaffa
Reading patterns in the sky
Star formation is a chaotic process, operating over a range of scales. This makes direct comparison between individual objects, whether observed or simulated, at best very difficult, and in many situations not very useful. We need unbiased statistical measures both to identify and classify the important structures; to enable a quantitative comparison of observed and simulated data; and thereby to reveal the underlying physics. I will describe a range of algorithms for detecting and quantising structure in star forming clouds and star clusters, using statistical and morphological metrics, and illustrate their application to a few representative sources.
30.10.2017 14:00
David Jones (IAC), and Petr Kabath (ASU)
1) Instituto de Astrofísica de Canarias, La Laguna; 2) Astronomical Institute of the Czech Academy of Sciences, Ondřejov
"Per aspera ad astra simul": an ERAMUS+ collaboration
Abstract
David Jones (IAC), and Petr Kabath (ASU)
"Per aspera ad astra simul": an ERAMUS+ collaboration
The "Per aspera ad astra simul" ("Through difficulties to the stars together") ERASMUS+ programme represents a strategic collaboration between the Instituto de Astrofisica de Canarias (IAC, Spain) and various institutions across the Czech Republic and Slovakia, with unique opportunities for students, postdocs and more senior researchers alike. In this talk, David Jones (via Skype) will introduce the IAC and its observatories, including the Roque de Los Muchachos Observatory - home to the World's largest optical telescope, the Gran Telescopio Canarias or GranTeCan. With Petr Kabath we will also highlight some of the planned activities of the ERASMUS+ programme, including student placements at the IAC and GranTeCan, Summer schools on astronomical observing techniques, and opportunities for Czech and Slovak institutions to host IAC researchers.
10.10.2017 14:00
Elias Kammoun
SISSA, Trieste - Italy
Probing the close environment of supermassive black holes through X-ray spectral and temporal approaches
Abstract
Elias Kammoun
Probing the close environment of supermassive black holes through X-ray spectral and temporal approaches
The spin is one of the fundamental observable properties of black holes (BHs). The spin measurement, particularly in active galactic nuclei (AGN), is of great interest for understanding the physical processes on scales ranging from the circumnuclear region out to the host galaxy. Among the various methods used to measure spins of accreting BHs, the detection of a strong relativistic reflection component in the X-ray spectra is potentially the most powerful, and it has been shown to provide robust results mainly in the least obscured sources. It would be then timely to test how reliable the reflection-based BH spin measurements that can be currently achieved are. I will present in the first part of my talk an attempt to answer this question through blind-fitting a set of simulated high-quality XMM-Newton and NuSTAR spectra, considering the most generic configuration of AGN spectra. Our main result shows that, in spite of their quality, single-epoch observations mostly return poor constraints on the actual BH spin value, except for the case of extreme relativistic effects. I will discuss also the possible impact of ATHENA in this field and how these limitations can be overcome.
In the second part of my talk, I will present the "flux-flux plots" method that can provide model-independent clues regarding the X-ray variability of AGN. We applied this method to simultaneous XMM-Newton and NuSTAR observations of MCG-6-30-15 and we were able to identify both a variable and a constant (over >4.5 days) component of the X-ray emission in this source. The variable emission is consistent with a primary plus relativistic reflection that are modified by warm absorption. While the constant emission consists of a blackbody (kT ~ 0.1 keV) responsible of the constant soft excess and a neutral reflection, from distant neutral material, dominating at energies above ~1.6 keV.
03.10.2017 15:00
Ivan L. Andronov
Odessa National Maritime University, Odessa, Ukraine
Magnetism in Interacting Binary Stellar Systems
Abstract
Ivan L. Andronov
Magnetism in Interacting Binary Stellar Systems
The highlights of the theoretical study and own photometrical (since 1978) and polarimetrical (1989) monitoring of magnetic cataclysmic variables are reviewed in a comparison to other magnetic binaries. The characteristic timescale of variability of these objects is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 364 ADS papers were published on these and other variable stars in a frame of the international "Inter-Longitude Astronomy" (ILA) project. In this short review, we present some highlights of observations and mathematical modeling of interacting binary stars of different types: classical (AM Her, QQ Vul, V808 Aur = CSS 081231:071126+440405, FL Cet), asynchronous (BY Cam, V1432 Aql), intermediate (V405 Aql, BG CMi, MU Cam, V1343 Her, FO Aqr, AO Psc, RXJ 2123, 2133, 0636, 0704) polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations.
03.10.2017 14:00
Ivana Ebrova
Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences
Galaxies with prolate rotation in the Illustris simulation
Abstract
Ivana Ebrova
Galaxies with prolate rotation in the Illustris simulation
Tens of early type galaxies have been recently reported to possess prolate rotation, i.e. significant amount of rotation around the major axis, including two cases in the Local Group. Although expected theoretically, this phenomenon is rarely observed and remains elusive. In order to explore its origin we study the population of well-resolved galaxies in the Illustris cosmological simulation. We follow their evolution back in time and find that the emergence of prolate rotation is strongly correlated with the time of the last significant merger the galaxy experienced, although other evolutionary paths leading to prolate rotation are also possible.
(https://arxiv.org/abs/1708.03311)
06.09.2017 14:00
Anna Saburova
Sternberg Astronomical Institute, Moscow M.V. Lomonosov State University
A study of star formation sites in tightly interacting systems
Abstract
Anna Saburova
A study of star formation sites in tightly interacting systems
On the example of three strongly interacting systems (Arp
270, Arp 194, NGC4656) we study the star forming sites in
the main bodies of the galaxies and in their vicinities:
gas and stellar kinematics, metal abundance and stellar age.
For this purpose we used the long-slit spectral observations
carried out at the Russian 6m telescope. All three systems
are very different in their star forming history. In Arp 270
the emission gas is well chemically mixed, whereas in Arp
194 there are strong velocity and abundance gradients
between the galaxies. In Arp 194 and NGC4656 we observe the
evidences of continuing gas accretion onto the galaxies. In
Arp194 we found a tidal dwarf candidate falling back into
the parent galaxy. The close low surface brightness
satellite interacting with NGC 4656 in contrast appears to
be a metal-poor discy dwarf galaxy resembling ultra-diffuse
galaxies where the mass of stellar population is low in
comparison with the mass of dark matter and HI.
03.07.2017 15:00
Kuantay Boshkayev
Faculty of Physics and Technology, Al-Farabi Kazakh National University, Almaty, Kazakhstan; and Dipartimento di Fisica and ICRA, Università di Roma `La Sapienza', Rome, Italy
White dwarfs and their astrophysical implications
Abstract
Kuantay Boshkayev
White dwarfs and their astrophysical implications
In my talk I will speak about classical and relativistic, cold and hot, static and rotating white dwarfs. The main attention will be drawn to the white-dwarf model of magnetars and the finite temperature effects in white dwarfs.
http://adsabs.harvard.edu/abs/2017MNRAS.464.4349B
22.06.2017 14:00
Abigail Stevens
Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands
Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing
Abstract
Abigail Stevens
Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing
X-ray spectral-timing is a new field that seeks to investigate how matter behaves in strong gravitational fields. Observations suggest that different types of low-frequency quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g., disk-like or jet-like) in the innermost part of the X-ray binary, close to the neutron star or black hole. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to Type B and Type C low-frequency QPOs from the black hole X-ray binary GX 339-4. On the QPO time-scale, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We can quantify how the spectral shape changes as a function of QPO phase, and the two different QPOs show markedly different spectral changes. In our previous work, we inferred that the Type B QPO could be caused by a large-scale-height (i.e., jet-like) precessing region illuminating and heating overlapping azimuthal regions of the inner accretion disk. Preliminary results of the Type C QPO indicate that a small-scale-height (disk-like) precessing region may be responsible for the observed spectral changes. This talk will feature results from this paper: https://ui.adsabs.harvard.edu/#abs/2016MNRAS.460.2796S/abstract
29.05.2017 14:00
Vojtěch Witzany
ZARM, University Bremen, Am Falturm 2, 28359 Bremen, Germany
Generalized conservation law near spinning black holes
Abstract
Vojtěch Witzany
Generalized conservation law near spinning black holes
Conservation of energy and angular-momentum fluxes is a well known property of the evolution of any matter field in any axisymmetric stationary metric. However, there is another flux corresponding to the „hidden symmetry“ of the Kerr space-time undergoing well-defined evolution which can be understood as a generalized conservation law. In this talk I derive the flux and its properties and discuss applications to simulations of accretion onto black holes.
20.03.2017 14:00
Bruno Leibundgut
ESO, Garching-bei-München, Germany
Observing with ESO telescopes
Abstract
Bruno Leibundgut
Observing with ESO telescopes
ESO offers a wide range of telescopes and instruments. Selecting the right combination for astronomical observations can be tricky and decisive for the project. I will present the ESO process to provide a better understanding of what is required by the proposer. The talk covers proposal preparation, selection, scheduling, observations and data products as returned from ESO. It will also will touch on related topics, like available instrumentation and their science capabilities, science archive, student- and fellowship programmes. Open discussion on all topics is encouraged.
27.02.2017 14:00
Robert Klement
Astronomical Institute, Faculty of Mathematics and Physics, Prague
Revealing the structure of the outer disks of classical Be stars - are Be disks circumbinary?
Abstract
Robert Klement
Revealing the structure of the outer disks of classical Be stars - are Be disks circumbinary?
Classical Be stars possess self-ejected gaseous circumstellar disks governed by viscous forces. The structure of the inner parts (<20 stellar radii) of these disks is well explained by the viscous decretion disk model (VDD), which is able to reproduce multi-technique observable properties of most of the so-far studied objects. Due to the nature of the emission mechanism responsible for the IR and radio continuum excess (free-free emission), the outer parts of the disks are observable at radio wavelengths only. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for the handful of Be stars that were observed in radio, but the physical reason for this feature remained mostly unknown.
I will present results from the multi-technique modeling of beta CMi, for which we obtained new sub-mm data from the APEX telescope. The SED turndown observed in beta CMi could be reproduced only when assuming a truncated disk. The most plausible explanation for the truncation is the presence of a faint companion, which has been just independently confirmed as predicted via RV analysis of the H-alpha line. Results from the SED modeling of 5 additional stars, 4 of which have new multiband VLA data, will be presented. All the studied disks are found to be truncated, while only one of the objects is a previously known binary. The detailed structure of the radio SED revealed by the VLA observations allow for studying the exact nature of the disk truncation. The truncation is clearly not as sharp as expected, and certain features indicate that the disks may extend beyond the orbits of the companions, thus offering a possibility that Be disks are actually circumbinary disks. Impacts of the suspected high binarity fraction of Be stars on their possible common evolutionary scenario will be discussed.
04.01.2017 14:00
Michal Zajaček
I. Institute of Physics, University of Cologne, Germany
What have we learned from the observations of the NIR-excess source DSO/G2 in the Galactic centre?
Abstract
Michal Zajaček
What have we learned from the observations of the NIR-excess source DSO/G2 in the Galactic centre?
The Dusty S-cluster Object (DSO/G2) orbiting the supermassive black hole (Sgr A*) in the Galactic centre has been monitored in both near-infrared continuum and line emission. There has been a continued discussion about the character of the object: interpreting it as either a core-less gas cloud or a dust-enshrouded star. A recent analysis of polarimetry data in K_s-band (2.2 μm) by Shahzamanian et al. (2016) allows us to put further constraints on the geometry of the DSO. I will present our recent results of the radiative transfer modelling, including NIR polarized continuum, and discuss possible models of the DSO/G2 in the context of Galactic centre stellar populations.
