Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
11.04.2016 15:00
Lukáš Ledvina
MFF UK Praha
Microlensing of distant quasars
Abstract
Lukáš Ledvina
Microlensing of distant quasars
In quasar microlensing, flux from a distant quasar is modulated by the gravitational lensing effect of individual stars in a galaxy lying in the foreground. The stars form a network of caustics that scan the surface of the quasar accretion disk passing in the background. Here we illustrate the effects of microlensing on the neutral iron Kα line emitted from the innermost disk. Changes in the line profile were most clearly observed by Chartas et al. (2012) in the lensed quasar RX J1131–1231. We use a fully relativistic Kerr-metric thin-disk model (Dovčiak et al. 2004) to demonstrate the connection between features of the line profile and the caustic position on the emission map of the quasar. In the future this method may prove to be a very powerful technique for spatially resolving the X-ray emission from the innermost accretion disk. We introduce a new fast numerical approach for calculating the specific flux from a (microlensed) accretion disk using GPU. In the future microlensing may prove to be a very powerful technique for spatially resolving the X-ray emitting region of the quasar.
29.04.2016 10:00
Simone Recchi
Astronomical Institute, Academy of Sciences, Prague
New ideas on the formation of globular clusters
Abstract
Simone Recchi
New ideas on the formation of globular clusters
Several ideas have been put forward in the recent past about the formation of globular clusters (GCs), but none of them seem to be fully satisfactory. In particular it is very challenging to explain the presence of multiple populations of stars and the anticorrelations between some light elements (in particular the Na/O and Mg/Al anticorrelations) within GC. For most of the proposed scenarios, in order to fit these anticorrelation the GC must lose a very large fraction of first generation stars, but it is unclear how to disperse such a huge fraction of stars. We propose here that first generation stars are formed in a supershell, swept up after the explosion of a very massive primordial star (the so-called popIII star). Since these supershell stars are born at some distance from the center of the GC, and since they inherit the outward-directed radial velocity of the supershell, it is likely that most of them will be unbound. On the other hand, a significant fraction of the ejecta of these supershell stars can propagate, almost unimpeded, towards the center of the GC. They pile up there, cool (because of the large densities reached in the center) and can form a new generation of stars. We will present in this seminar the details of this scenario and 1-D chemo-dynamical simulations corroborating it.
Previous seminar:
21.03.2016 16:00
Michal Zajaček
I. Institute of Physics, University of Cologne, Germany
An update about Dusty S-cluster object (DSO/G2) near the supermassive black hole
Abstract
Michal Zajaček
An update about Dusty S-cluster object (DSO/G2) near the supermassive black hole
I will briefly summarize our recent findings about the DSO/G2 infrared-excess object that is now in its post-peribothron phase. In particular, I will show my models that can explain the basic observational characteristics of the object. In the end, I will present a generalized model of the star-ambient medium interaction near Sgr A* and how it can be used to constrain the properties of the interstellar medium in the immediate vicinity of the supermassive black hole.
If you would like to give a seminar in our group, please contact Vladimir Karas or Jaroslav Hamersky.
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