WP4: Radiative processes in solar and stellar atmospheres

The research on stellar radiative processes mainly concerns empirical and theoretical aspects of the spectral and photometric variability of various types of variable stars. On the other hand, the research on radiative processes in the solar atmosphere embraces basic mechanisms of emission in the solar atmosphere, especially from the solar chromosphere, i.e., the continuum radiation (thermal and non-thermal bremsstrahlung) and the spectral line emission. The research in this field provides a better understanding of plasma instabilities and plasma emission mechanisms, comprehension of the physical state of solar and stellar atmospheres, as well as MHD and HD processes in circumstellar space.


T4.1. Spectroscopic and photometric properties of variable stars

The research related to the stellar radiative processes will be focused on various aspects of the physics of stellar atmospheres and binary stars. It is primarily based on continuous photometric monitoring of various stellar objects. The research encompasses spectroscopic and photometric properties of Be stars, Be shell stars and selected eclipsing binary stars, observations and interpretation of light variations of variable stars in galactic clusters and selected Ap stars, the light variability of pulsating red giants, and classic chemically-peculiar magnetic stars. In addition, the research will make use of the discovery and characterization of variable stars employing the LINEAR sky survey data base. The empirical aspect of T4.1 is based on both the archived and newly measured data provided mainly by Hvar Observatory 65-cm and 1-m telescopes, Ondrejov Observatory 2-m spectrographic telescope (Czech Republic), and the LINEAR sky survey data.


T4.2. Circumstellar and accretion-disc matter

The research within T4.2 considers the influence of the circumstellar matter to the radiation field of eclipsing binaries, the light variability of young stars due to their accretion disks, and numerical HD and MHD modelling of accretion and discs. The empirical aspect of T4.2 is based on both the archived and newly measured data provided mainly by Hvar Observatory 65-cm and 1-m telescopes, as well as the Ondrejov Observatory 2-m spectrographic telescope (Czech Republic).


T4.3. Investigation of the solar He I 1083 nm spectral line

The research in the scope of T4.3 concerns the formation of the He I 1083 nm spectral line in the solar atmosphere. This line provides a unique insight into both chromospheric and coronal plasma processes on the Sun. The archived full-disc solar images in the He I 1083 nm line obtained with the ChroTel instrument installed at the Vacuum Tower Telescope, German Solar Telescopes at Izana, Tenerife are used to study the evolution of coronal holes, evolution of CMEs and coronal waves, and enhanced helium absorption at the feet of coronal loops.


T4.4. Analysis of solar plasma with ALMA

The research within T4.4 is related to solar observations that will be performed with the new system of radio telescopes, ALMA (Atacama Large Millimeter/submillimeter Array). Solar measurements performed with ALMA are used to test models of the solar radiation at mm and sub-mm wavelengths relying on various radiation mechanisms applied to different models of the solar atmosphere. In addition, the coronal and chromospheric heating and centre-to-limb brightness variation of the Sun at mm and sub/mm wavelengths are also investigated.