Věda a výzkum

Přednášky a semináře

Semináře pořádáme nově s čtvrtletní periodou a s bohatším obsahem.

Příští seminářové odpoledne (od 13h)

01. 06. 2015
Jan Palouš
Multi-Generation Star Clusters
Abstract: Massive star clusters are essential components of galaxies. When they form and during their early times they influence the surrounding interstellar medium with radiation, winds and supernova ejecta. This stellar feedback removes the gas out of the parent molecular cloud, star cluster expands, and in many cases it dissolves completely. Remaining globular star clusters reside in galaxy haloes. The model of massive star cluster formation as the monolithic collapse of the parent molecular cloud needs to be revisited due to discovery of multiple stellar generations of long-lived stars in globular clusters. We propose a new "cooling winds model" explaning formation of the second stellar generation out of matter that is enriched by H-burning products of the first stellar generation. Above a critical mass of the star cluster, winds form thermally unstable clumps reducing locally the temperature and pressure of the hot 10^7 K cluster wind. The matter reinserted by stars, and mass loaded in interactions with pristine gas and with evaporating circumstellar disks, accumulates in clumps that are ionized with photons produced by massive stars. We shall discuss if they may become self-shielded when they reach the central part of the cluster, or even before it during their free fall to the cluster center. We shall explore the importance of early mass loading of the stellar winds, and we shall analyse the role of additional cooling by dust produced in supernova events.
01. 06. 2015
Jaroslav Dudík
Non-Maxwellian distributions in the solar corona
Abstract: Observations of the solar wind show pervasive presence of the non-Maxwellian kappa-distributions of electron energies characterized by a power-law high-energy tail. Theory has shown that such distributions can arise in the solar corona during impulsive heating by magnetic reconnection and also wave-particle interactions. We explored the consequences of the presence of such kappa-distributions on the optically thin spectra of the solar corona emitted in the X-rays, UV, and visible wavelengths. In particular, several line combinations allow for diagnostics of the kappa-distributions. A diagnostic from the EUV line ratios observed by Hinode/EIS space-borne spectrometer is performed and it is shown that the electron distribution can be strongly non-Maxwellian.
01. 06. 2015
Grigorios Maravelias
High-Mass X-ray Binaries in the Small Magellanic Cloud
Abstract: High-Mass X-ray Binaries (HMXBs) are a phase in the life of some binary stellar systems that consist of a compact object (black hole or neutron star) and a massive companion (an early OB-type star). Their X-ray emission is powered by the infall of matter, provided by the massive companion, into the strong gravitational field of the compact star. The Small Magellanic Cloud (SMC) is a powerhouse of HMXB production (almost 100 systems), and due to its proximity we are able to investigate individual sources. However, we haven't yet fully characterize its HMXB population. To address that we have initiated wide spectroscopic and Halpha imaging campaigns. I will discuss our results and how the SMC HMXB population compares with that of our Galaxy.
01. 06. 2015
Tomáš Henych
Subcatastrophic collisions between asteroids
Abstract: Mutual collisions between asteroids affect their size distribution, spins and surface morphology. Subcatastrophic collisions may be responsible for an excited asteroid rotations. We created a numerical model to investigate this hypothesis and also other effects of small collisions between asteroids. Recently, we showed that erosion caused by collisions increases the elongation of asteroid shapes on a timescale much longer than their collisional lifetime.

 

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.

Program seminářů

09/06/2015, 13:00
Dieter Nickeler
The boundaries between stellar winds and their local interstellar medium: astropauses and astrotails
Abstract: As in hydrodynamics or aerodynamics, where streamlined bodies or aerofoils constitute obstacles for the surrounding, streaming medium, stars with their stellar winds form obstacles for the flowing interstellar medium (ISM). Due to the interaction between the two plasmas with their electromagnetic fields, separating surfaces can form, if the magnetic field is in good approximation frozen into the plasma flow. These boundaries, separating both plasmas, are called astropauses. The stellar wind within the astropause can be deflected into a so called astrotail. We will discuss under which circumstances astropauses are formed and what determines their shapes and the connectivity of field lines and streamlines.

 

Semináře oddělení GPS

Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.

Program seminářů

10. 08. 2015, 15:00
Norbert Werner
Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
How supermassive black holes and star-formation sculpt the visible Universe
Abstract: In the course of structure formation, only a small fraction of the baryons turned into stars - most remain in a diffuse intergalactic medium. The growth of galaxies is regulated by feedback processes, such as energy and momentum input from supernovae, and jets and winds of accreting supermassive black holes. These processes, collectively called galactic feedback, can limit or even inhibit star formation, and thus a detailed knowledge of how they work is essential for our understanding of galaxy formation and evolution. I will start my talk by presenting recent observational results on the role of supermassive black holes in keeping the most massive galaxies 'red and dead'. Then, I will 'zoom out' to the outskirts of galaxy clusters where we also find hints that supermassive black holes played an important role in the distant past. X-ray observations with the Suzaku satellite reveal a remarkably homogeneous distribution of iron out to the virial radius of the nearby Perseus Cluster, requiring that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. Finally, I will talk about the upcoming ASTRO-H satellite which will revolutionize X-ray spectroscopy and our understanding of how feedback processes couple to the intergalactic medium.
(Takes place at: Sporilov library)

 

Semináře stelárního oddělení

Ve čtvrtek od 14:00 v seminární místnosti stelárního oddělení.

Program seminářů