Přednášky a semináře
Astronomický ústav AV ČR pořádá celoústavní semináře, kde se představuje každé vědecké oddělení - Stelární oddělení, Sluneční oddělení, Oddělení meziplanetární hmoty a Oddělení galaxií a planetárních systémů, a to jak organizačními novinkami z oddělení, tak jednou nominovanou přednáškou na vědecké téma. Semináře pořádáme se zhruba čtvrtletní periodou v půldenním bloku.
Drift of the Erupting Flux Rope Footpoints: Theory and Observations
Solar flares belong to the most geo-effective manifestations of solar activity and they are powered by magnetic reconnection. We present an analysis of 2015-Nov-04 eruptive flare which exhibited a drift of the footpoints of an erupting flux rope. Such a drift has been recently predicted by the extensions to the standard solar flare model in 3D as a consequence of 3D reconnection geometries involving also flux rope field lines. Then we briefly report on other flare events to show that these 3D reconnection geometries are common features observed during eruptive flares. Our results indicate that the dynamics in eruptive flares are richer than previously thought, with consequences for the mass loading of eruptions and their
Physical properties of Taurid meteoroids of various sizes
aurids is a well-known annual meteor shower but it origin is still debated. Short period comet 2P/Encke is the most probable parent body of the shower but various asteroids were proposed to be members of the so-called Taurid complex as well. It was also proposed that 2P/Encke is just one fragment of a much larger comet, which disrupted tens of thousands years ago.
Pavel Spurný presented a discovery of a resonant Taurid branch, which is responsible for enhanced activity of the shower in some years. Here we used a well defined orbital sample of 16 Taurid fireballs with detailed radiometric light curves to study physical properties of Taurid meteoroids. The sample represented meteoroids of initial masses from 8 grams to 650 kg (diameters 1-70 cm). Our semi-empirical fragmentation model was used to study their atmospheric fragmentation and derive strength distribution within the meteoroids. We found that Taurids are of cometary origin and the material contains significant inhomogeneities.
Predicting spectra and spectral classes of low-metallicity massive single stars with rotation
Metal-poor massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and compact object mergers that might contribute to the early epochs of the Universe with their strong ionizing radiation. However, this assumption remains mainly theoretical because individual spectroscopic observations of such objects have rarely been carried out for metallicities lower than that of the Small Magellanic Cloud.
We will present the predictions of the state-of-the-art theories of stellar evolution combined with those of stellar atmospheres about a certain type of metal-poor (0.02 Z⊙) hot massive stars, the chemically homogeneously evolving stars. We computed synthetic spectra corresponding to a broad range in masses (20−130 M⊙) and covering several evolutionary phases from the zero-age main-sequence up to the core helium-burning stage. We investigated the influence of mass loss and wind clumping on spectral appearance and classified the spectra according to the Morgan-Keenan system.
Mapping the transformation of galaxies in intermediate redshift clusters
By using adaptive binning of on-the-sky positions of galaxies, members of clusters at intermediate redshifts, we produce maps of galaxy properties which we use to constrain the locations where different environmental processes take place. The main targets are two clusters at the same
redshift but at different evolutionary stage, which are compared with 30 other clusters from the ACReS survey. A520 is a major cluster merger while A963 is relatively relaxed massive cluster which shows strongly
anisotropic accretion of galaxies. Using optical spectroscopy and ultra-deep 21cm imaging, phase space analysis, as well as mapping of the large-scale structure of the universe in extended regions around the
clusters we reveal the combined effects of ram-pressure stripping and pre-processing that produce the low redshift clusters dominated to a various degree by passive galaxies.
Archiv minulých seminářů
Dále se konají menší tématické semináře jednotlivých oddělení:
Semináře slunečního oddělení
Vždy ve čtvrtek od 11:00 (září–červen) v zasedací místnosti slunečního oddělení pracoviště Ondřejov.
Penumbral brightening events
We studied brightening events observed in the penumbra of one among the largest sunspots emerged into the solar atmosphere over the last activity cycle, by using multi-wavelength observations from the IBIS spectropolarimeter and instruments onboard the SDO, IRIS, and Hinode satellites. We focused on the evolution of a penumbral area that was adjacent to two small-scale emerging flux regions (EFRs). We found that these regions and short-living magnetic features (MMFs) moving away from the penumbra led to reconfiguration of the magnetic fields in the studied area. Besides, we found that the studied brightening events likely derived from reconnection processes occurred at different atmospheric heights that were activated by the interaction of the pre-existing fields with either the EFRs or MMFs.
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.