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.
Outflows from evolved stars
In my PhD Thesis we study the origin of powerful stellar outbursts in the late phases of evolution of stars like the Sun. This is one of the most controversial topics in the field, as the extraordinary variety of shapes revealed by observations are not expected to be the result of the evolution of stars that are basically spherical all over their lives. The stellar explosions that we are studying (GK Persei, R Aquarii) occur and develop on time-scales of years, even months. This allows us to study their evolution in real-time, a very rare opportunity in Astrophysics. To this aim, we have gathered over the years a unique collection of high-resolution images, from which we produce "movies" that reveal the expansion of the nebulae as projected in the plane of the sky. Images are complemented by spectra that measure the line-of-sight velocities, also required to build 3D models of the dynamical evolution of the outflows, a privileged information for theoretical modelling.
Simulating the interstellar medium, and its synthetic emission
To understand the dynamics and composition of the gas in the interstellar medium (ISM), numerical simulations are used to study its evolution. Such simulations can apply to different spatial scales and serve as a laboratory to track the evolution on long time scales. I will present simulations modeling the ISM within a piece of a galactic plane, as done within the SILCC project (Simulating the Life Cycle of molecular Clouds, project led by Stefanie Walch-Gasser), and within one single molecular cloud, as done in the SILCC-Zoom project (Daniel Seifried).
To further investigate what these simulations tell us about the ISM we observe, it becomes important to compare both sides. For this the synthetic emission of different lines of those simulations is estimated, and in a further step compared to observations. In the second part of the talk I will show some results concerning the synthetic [CII] line emission from carbon ions. This line is especially interesting due to its possible potential as a tracer of CO-dark molecular gas and of the star formation rate in galaxies.
Finally, I will talk about simulating the X-ray emission from star clusters (Richard Wünsch, Dorottya Szécsi, Sergio Martínez González). These models are suited for comparison with the X-ray emission of Green Pea Galaxies, which are compact objects with a high star formation rate and a low metallicity (Ivana Órlitova, Jiri Svoboda). Green Peas might be one source of escaping ionizing radiation responsible for the reionization of the Universe after the Dark Ages.
A piece of the puzzle of dissipation in flares and coronal heating: non-linear 3D flows inducing fragmented currents
Many magnetic structures in the solar atmosphere evolve rather slowly so that they can be assumed as (quasi-)static or (quasi-)steady and represented via magneto-hydrostatic (MHS) or magneto-hydrodynamic (MHD) equilibria, respectively. While exact 3D solutions would be desired, they are extremely difficult to find in steady MHD. We construct solutions with magnetic and flow vector fields that have three components depending on all three coordinates. We show that the non-canonical transformation method produces quasi-3D solutions of steady MHD by mapping 2D or 2.5D MHS equilibria to strongly related steady-MHD states, displaying highly complex currents. The existence of geometrically complex 3D currents within symmetric field-line structures provide the base for efficient dissipation of the magnetic energy in the solar corona by Ohmic heating. We also discuss the possibility of achieving force-free fields, and find that they only arise under severe restrictions of the field-line geometry and of the magnetic flux density distribution.
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.
Chromospheric observations and magnetic configuration of a supergranular structure
We present high spatial resolution narrow-band images in three different
chromospheric spectral lines, including Ca II K with the new CHROMospheric
Imaging Spectrometer installed at the Swedish 1-m Solar Telescope. These
observations feature a unipolar region enclosed in a supergranular cell, and
located 68 deg off the disk-centre. The observed cell exhibits a radial
arrangement of the fibrils which recalls of a chromospheric rosette. However,
in this case, the convergence point of the fibrils is located at the very
centre of the supergranular cell. Our study aims to show how the chromosphere
appears in this peculiar region and retrieve its magnetic field and velocity
distribution. In the centre of the cell, we measured a significant blue-shift
in the Ca II K nominal line core associated to an intensity enhancement. We
interpreted it as the product of a strong velocity gradient along the line of
sight. In this talk, we will discuss the techniques employed to obtain
magnetic field maps so close to the limb and suggest a possible configuration
that takes into account also the measured velocity within the unipolar
Semináře oddělení GPS
Obvykle v pondělí od 14 hod v přednáškové místnosti pracoviště Praha–Spořilov.