Přednášky a semináře
Semináře pořádáme nově s čtvrtletní periodou a s bohatším obsahem.
Příští seminářové odpoledne (od 13h)
18. 01. 2017
Dynamics of solar prominences
Abstract: Solar prominences are one of the manifestations of the solar activity. In filtergrams they appear as dark elongated structures on the background of solar photosphere (then called filaments) or as a bright objects above the solar limb. Using spectroscopic methods their Doppler velocity in the line-of-sight may be measured. This information may be further analyzed in two ways. In the first method oscillations of a prominence in the plane-of-the-sky may be detected. The results of analysis of oscillations along with modeling can bring us information of physical parameters in prominences, which is very valuable in so called prominence seismology - one of the branch of solar physics. The second way is to analyze Doppler velocity variation of so called knots in an observed prominence and to combine it with motion in the plane-of-the-sky. As a result full 3D knot trajectory may be constructed, which determines magnetic field topology. In the talk I will present results of observations of prominence dynamics with different telescopes of several prominences as well as synthetic models of oscillating prominence slab.
Archiv minulých seminářů
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.
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.
27. 02. 2017, 14:00
Revealing the structure of the outer disks of classical Be stars - are Be disks circumbinary?
Abstract: Classical Be stars possess self-ejected gaseous circumstellar disks governed by viscous forces. The structure of the inner parts (<20 stellar radii) of these disks is well explained by the viscous decretion disk model (VDD), which is able to reproduce multi-technique observable properties of most of the so-far studied objects. Due to the nature of the emission mechanism responsible for the IR and radio continuum excess (free-free emission), the outer parts of the disks are observable at radio wavelengths only. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for the handful of Be stars that were observed in radio, but the physical reason for this feature remained mostly unknown.
I will present results from the multi-technique modeling of beta CMi, for which we obtained new sub-mm data from the APEX telescope. The SED turndown observed in beta CMi could be reproduced only when assuming a truncated disk. The most plausible explanation for the truncation is the presence of a faint companion, which has been just independently confirmed as predicted via RV analysis of the H-alpha line. Results from the SED modeling of 5 additional stars, 4 of which have new multiband VLA data, will be presented. All the studied disks are found to be truncated, while only one of the objects is a previously known binary. The detailed structure of the radio SED revealed by the VLA observations allow for studying the exact nature of the disk truncation. The truncation is clearly not as sharp as expected, and certain features indicate that the disks may extend beyond the orbits of the companions, thus offering a possibility that Be disks are actually circumbinary disks. Impacts of the suspected high binarity fraction of Be stars on their possible common evolutionary scenario will be discussed.