Přednášky a semináře
Semináře pořádáme nově s čtvrtletní periodou a s bohatším obsahem.
Příští seminářové odpoledne (od 13h)
14. 03. 2016
On the direct detection of gravitational waves
Abstract: Current information about recent announcement of the first in history detection of gravitational waves.
14. 03. 2016
The past activity of the Galactic centre
Abstract: Despite the low level of current activity in the Galactic centre, X-ray reflection from molecular clouds in the Sgr A* region indicates that the supermassive black hole was orders of magnitude brighter just a few hundred years ago than it is currently. We investigate the idea of the Galactic centre minispiral as the origin of gaseous material for the enhanced past activity of Sgr A*.
Collisions between clumps of gas in the minispiral can reduce their angular momentum and set some of the clumps on a plunging trajectory towards the supermassive black hole. We demonstrate that the amount of material contained in the minispiral is sufficient to sustain the luminosity of Sgr A* at the required level. We also study the possibility of the formation of thermal instability in the two-phase minispiral region, enhancing the accretion of clouds by the central black hole.
14. 03. 2016
Evolution of binary near-Earth asteroids
Abstract: To date, about 50 binary near-Earth asteroids, 20 Mars-crossing and 80 small Main Belt binary asteroids are known, most of which were observed within our programme. For three of them we have data spanning more than 14 years, which allow us to study their long-term evolution.
Orbits of natural satellites of asteroids are subject to tidal evolution and the so-called BYORP effect, causing shrinking or expanding of orbit due to solar radiation pressure. If the BYORP
effect is removing angular momentum from the orbit of the satellite, a counterbalance of BYORP and mutual tides can result in a long-term stable solution. I will show the observational evidence of two Binary asteroids with tidally locked satellite and one with long-term evolution of the satellite's orbit.
The observations of long-term evolution have important implications for asteroid geophysics. From the equilibrium between mutual tides and the BYORP effect we can derive a rigidity of the main body, allowing us to reveal whether it has monolithic structure or it is the so-called 'rubble-pile'.
14. 03. 2016
High-resolution fine-structure synthetic imaging of an entire prominence using 3D whole-prominence fine structure modelling
Abstract: The newly developed 3D whole-prominence fine structure (WPFS) model (Gunár & Mackay 2015) allows us for the first time to simulate entire prominences/filaments including their numerous fine structures. This model combines a 3D magnetic field configuration of an entire prominence obtained from non-linear force-free field simulations, with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along hundreds of fine structures within the 3D magnetic model. The prominence plasma has realistic density and temperature distributions including the prominence-corona transition region.
To produce the high-resolution synthetic H-alpha images of the WPFS model we use a novel fast approximate radiative transfer visualization technique (Heinzel et al. 2015). This allows us for the first time to produce images of the prominences in emission on the solar limb and filaments in absorption against the solar disk using a single model. The prominence plasma and magnetic field are described in the WPFS model on scales that allow us to produce synthetic images with resolution matching that of the state-of-the-art Hinode/SOT observations, or indeed that of the upcoming solar observatories, such as DKIST or Solar-C. Moreover, to complement the prominence/filament synthetic images we have consistent information about the magnetic field and plasma parameters everywhere in the modelled prominences. This allows us to investigate the apparent puzzling nature of the observed
prominence and filament fine structures. We can also study the connections between the local configuration of the magnetic field and the observable structure of the finest prominence/filament features. In addition, we are able to investigate the prominence evolution. We can consistently study the influence of the varying photospheric flux distribution on the prominence magnetic field configuration and its effect on the observable prominence plasma.
14. 03. 2016
Study of Gamma-Ray Bursts With Robotic Telescopes
Abstract: I will talk about gamma-ray bursts (GRBs), observed as brief flashes of gamma radiation of cosmic origin. The phenomena, now considered one of the most energetic phenomena in the universe, was discovered in 1967.
Nowadays, with specialized satellites, GRBs are detected and localized automatically, and triggers are generated and sent to ground-based robotic telescopes. This way, a multi wavelength studies, employing data ranging from gamma-rays through X-rays and optical to radio wavelengths, permit a complex view onto these events, since the discovery of the afterglows - the emission on other wavelengths in 1997.
I will provide a very brief introduction into the GRB physics, followed by a few examples of studies of individual gamma-ray bursts. Then I will briefly present an effort done to summarize all the successful GRB follow-ups performed by BOOTES-1B and BOOTES-2 during the past decade. The last few minutes will be dedicated to the Compact Low Resolution Spectrograph (COLORES), a lightweight FOSC instrument we developed and have been successfully operating at BOOTES-2 since 2012.
Dále se konají menší tématické semináře jednotlivých oddělení:
Semináře slunečního oddělení
Vždy v úterý ve 13:00 (září–červen, s výjimkou úterků po celoústavním semináři) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
17/05/2016, 13:00
Hybrid simulations of chromospheric HXR flare sources
Abstract:
Recent measurements of vertical extents and positions of the chromospheric hard X-ray (HXR) flare sources based on Ramaty High-Energy Spectroscopic Imager (RHESSI) observations show a significant inconsistency with the theoretical predictions based on the standard collisional thick target model (CTTM). Using a hybrid flare code Flarix, we model simultaneously and self-consistently the propagation, scattering and energy losses of electron beams with power-law energy spectra and various initial pitch-angle distributions in a purely collisional approximation and concurrently the dynamic response of the heated chromosphere on timescales typical for RHESSI image reconstruction. The results of the simulations are used to model the time evolution of the vertical distribution of chromospheric HXR source within a singular (compact) loop. Adopting the typical RHESSI imaging times scales, energy dependent vertical sizes and positions as could be observed by RHESSI are presented.
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.
27. 05. 2016, 10:00
New ideas on the formation of globular clusters
Abstract: 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.
(Takes place at: to be confirmed)