Pravidelné semináře pořádáme jednou měsíčně (říjen–červen, zpravidla první pondělí v měsíci) od 13 hod v seminární místnosti pracoviště Ondřejov. (archiv seminářů)
16. 05. 2012
Massive star magnetospheres: from X-ray to radio
Abstract: Magnetic massive stars experience confinement of stellar wind plasma by their strong, large-scale magnetic fields. This magnetospheric material can produce observable spectral and photometric effects in wavelengths from X-rays to radio. I will present a summary of the observational and theoretical efforts to study massive star magnetospheres, as well as discuss future possibilities for these stars in the infrared.
Dále pořádáme menší semináře jednotlivých oddělení:
Semináře slunečního oddělení
Každé úterý v 13:00 (září–červen, s výjimkou úterků po celoústavním semináři) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
22/05/2012, 13:00Influence of static and stochastic electric fields on electron beams bombarding the chromosphereAbstract: The Collisional Thick Target Model - CTTM of the impulsive phase of solar flares presented for many years a successful attempt to interpret the processes related to the energy deposition and hard X-ray production in the footpoint regions of flare loops. With the onset of the new generation of HXR observations, obtained by e.g. RHESSI, continuously growing number of problems with the CTTM were beginning to appear. To resolve the discrepancies a modification of the CTTM known as the Local Re-acceleration Thick Target Model -- LRTTM has recently been proposed assuming an actuation of stochastic electric fields on the propagating beam electrons in the thick target region. We propose another modification of the CTTM the Global Re-acceleration Collisional Thick Target Model -- GCTTM which asumes an actuation of static electric fields, arising from the helicity of the individual magnetic field-lines in flare loops, on the propagating electron beam along the whole beam trajectory from the coronal primary acceleration site downwards to the chromosphere. In our contribution we will present a comparison of both modifications of the CTTM with the CTTM itself in sense of chromospheric flare heating, the electron beam distribution functions and the HXR spectra. The presented results are obtained using a relativistic test-particle approach.
Zářivě-(magneto)hydrodynamické semináře
Zpravidla 1x za 14 dní ve čtvrtek od 11 hod (říjen–červen) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
01/12/2011, 11:00Konkoly Observatory, Budapest, HungaryThe extreme outburst of the young eruptive star EX Lupi in 2008Abstract: EX Lupi is the prototype of EXors, a spectacular group of low-mass pre-main sequence stars characterized by repetitive optical outbursts of 1-5 mag lasting for a few months-to-few years. The outburst is attributed to enhanced accretion from the inner circumstellar disk (within ^X0.1AU) to the stellar surface, probably triggered by an instability in the disk. The historically largest outburst of EX Lupi in 2008 Jan-Sep offered a unique opportunity to understand deeper the physics of the EXor eruptions. In my talk I will summarize the main results of our coordinated observing campaign, in which we used a large set of telescopes to observe and characterize the path of accretion from the disk onto the stellar surface, with the aim of comparing the different models of outburst physics. Our measurements also demonstrated that the brief episodes of highly increased accretion, apart from contributing to the build-up of the final stellar mass, have substantial effect on the structure and composition of the circumstellar material: We discovered episodic crystallization of silicate grains in the disk surface due to the increased luminosity during the 2008 outburst, resulting in material that forms the building blocks of comets and planets.
Semináře oddělení GPS
Zpravidla v knihovně pracoviště Praha–Spořilov v různé dny.
28. 05. 2012, 14:00Ludwig-Maximilians-Universitaet, MunichCosmology and cluster astrophysics with the South Pole TelescopeAbstract: The South Pole Telescope (SPT) is 10-meter telescope operating at millimeter wavelengths whose primary goal is to search for clusters of galaxies via the Sunyaev-Zel'dovich (SZ) effect - the distortion of the cosmic microwave background imprinted by the hot intercluster plasma.
The mass and redshift distribution of the cluster population is sensitive to the geometry of the Universe and to the rate of structure growth. Galaxy clusters thus provide important insights into cosmological questions such as the nature of cosmic acceleration and the Gaussian character of underlying density perturbations. They can also serve as a consistency test of the general theory of relativity on cosmological scales.
I will explain the principles of cluster cosmology and give an overview of the SPT survey. I will discuss the current cosmological constraints from the SPT cluster data, highlighting the constraints on the dark energy equation of state, and the sum of the neutrino masses. I will also demonstrate the use of SPT clusters to answer astrophysical questions such as the cosmic evolution of gas cooling in the cluster cores and give examples of interesting individual systems discovered by SPT, raging from spectacular merging clusters to the most massive relaxed objects in the Universe.(Takes place at: Sporilov library)