Seminars
Our seminars take place in the lecture room of the building at
Praha–Sporilov.
Next seminar:
11.12.2017 10:00
Lecture Days
(1) University of Cologne (1. Physikalisches Institut); (2) Astronomical Institute of the Czech Academy of Sciences; (3) Charles University in Prague (Faculty of Mathematics and Physics)
Cologne–Prague Workshop
Abstract
Lecture Days
Cologne–Prague Workshop
Monday (Prague):
o Ondrej Pejcha, Explosive deaths of stars: core-collapse supernovae and stellar mergers
o Hirofumi Noda, Structures of Accreting Matters in AGNs Revealed by X-ray and Optical Monitoring and X-ray Microcalorimeter Spectroscopy
o Tayebeh Tahamtan, Nonlinear Electrodynamic in General Relativity
Tuesday (Prague):
o Anabella Araudo, On the maximum energy of particles accelerated in the termination shocks of AGN jets
o Georgios-Loukes Gerakopoulos, Chaos, entropy and black holes
o Marzieh Parsa, Parameter Estimation via MCMC
Wednesday (Ondrejov):
o Petr Kabath, tbd
19.12.2017 10:00
Vlastimil Vojacek
Astronomical Institute, Academy of Sciences, Ondrejov
Properties of faint meteors studied by video observations
Abstract
Vlastimil Vojacek
Properties of faint meteors studied by video observations
Parallel double-station video observations paired with spectroscopic video observations are a good way to study millimetre-sized meteoroids. Almost two decades of video observations of meteors at the Ondrejov observatory give us broad database to study large quantities of meteoroids and their properties.
In this work we combined spectral video observations and results of the modelling of the fragmentation of meteoroids. Along with complex information about meteoroid's trajectories and orbits, this can give us better understanding about origin, internal structure etc. of these millimetre-sized interplanetary bodies.
Meteoroids that contained small grains tend to release the sodium early. Since there is a smaller amount of sodium for Na depleted meteoroids, the sodium was released earlier than it was released for meteoroids with same grain sizes and without the sodium depletion. Overall, meteoroids with sodium depletion showed different composition: they were composed of stronger material without very small grains and they did not showed very bright wakes. Two iron meteoroids on Halley type orbits were observed. They are probably remnants of complicated early years of our solar system. The distribution of grain sizes of Jupiter-family members was in a good agreements with results from the COSIMA instrument from the ROSETTA mission.
19.12.2017 14:00
Silke Britzen
Max-Planck-Institut für Radioastronomie, Bonn, Germany
High-resolution radio interferometry: from jets to the supermassive black hole
Abstract
Silke Britzen
High-resolution radio interferometry: from jets to the supermassive black hole
Very Long Baseline Interferometry (VLBI) observations provide the highest resolution information in Astronomy. They allow us to study the jets and the immediate vicinities of the active supermassive black holes in galaxies. In my talk, I will present our most recent results on two prototypical active black holes. OJ287 is the best candidate galaxy for hosting a supermassive binary black hole at very close separation. To our knowledge, this is the first time we can explain the historic light-curve variability and long-term jet kinematics in geometrical terms - by jet precession and jet rotation. The jet might be launched from the ergosphere of the active black hole. For the nearby, giant radio galaxy M87 with a supermassive black hole of 10^9 solar masses, we find strong indication for turbulent processes connecting the accretion disk and the jet. For both active galaxies we can provide insights into the long-standing problem of the origin of astrophysical jets.
Previous seminar:
30.11.2017 14:00
Vanesa Douna
Instituto de Astronomía y Física del Espacio, Buenos Aires, Argentina
Exploring the impact of XRBs during reionization of the Universe
Abstract
Vanesa Douna
Exploring the impact of XRBs during reionization of the Universe
Reionization is one of the main cosmological phase transitions of the Universe. Observational evidence shows that ~1Gyr after the Big Bang, the intergalactic medium was ionized, although it had become neutral much before, when the Cosmic Microwave Background was released ~0.3 Myr after the Big Bang. Despite the increasing knowledge of the Epoch of Reionization in light of the new observational skills, the sources of reionization are still being debated. Although UV photons from massive stars seem to be the main reionization agents, X-rays from accreting black-hole populations and cosmic rays have also been considered. In this talk, I will summarize two of the main results of my PhD research, that intend to explore the effect of stellar accreting sources at cosmic dawn.
The importance of the effect of high mass X-ray binaries (HMXBs) on the primordial Universe depends on the hypothesized increase in the number and luminosity of HMXBs in low-metallicity galaxies. In the first place, to test this hypothesis we compile from the literature a set of observational data and, by means of Bayesian inference, we fit simple Monte Carlo models for the dependence on metallicity of the size and luminosity of the HMXB populations. We find that HMXBs are typically ten times more numerous per unit star formation rate in low-metallicity galaxies (namely <20% solar) than in solar-metallicity galaxies.
A subgroup of X ray binaries, known as microquasars (MQs), exhibit powerful relativistic jets that interact with the surrounding medium. We explore the contribution of electrons accelerated in the jets of high-redshift microquasars to heating and ionizing the intergalactic medium (IGM). We develop Monte Carlo simulations of the propagation and energy deposition of these electrons as they travel away from the source to the IGM. We find that MQs contribute significantly to heating the intergalactic medium and are effective ionizers only near the galaxies.
If you would like to give a seminar in our group, please contact Petra Sukova or Vladimir Karas.
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