Astronomical Institute AS CR Academy of Sciences CR
Astronomical Institute,
Academy of Sciences of the Czech Republic

Working Group of Physics of Hot Stars

Research of the working group is focused on hot stars. Observational research in stellar astronomy in Ondřejov is closely connected with the 2-m telescope and its spectrographs. Since the beginning of operation of the 2-m telescope in the early seventies, there has been an interest in observations and analysis of Be stars. Many Be stars were monitored continuously since that time and results of this effort offer unique sets of data describing the stellar activity and variability on various time-scales. These spectroscopic data supplemented by observations from other observatories and also by photometric observations formed a base of a number of scientific publications. Also, international campaigns for joint spectroscopic and interferometric observations of selected targets are being organized with the aim of improving binary parameters (e.g., the inclination, mass) and constraining the properties of Be star envelopes (e.g., shape, inclination). Due to the significant improvements of the 2m telescope carried our recently, our observational interests have extended to fainter objects. And, consequently research was extended to include studies of B[e] stars.

The winds and disks around massive stars in their late evolutionary phases formed by non-spherical mass-loss are studied, as well as the influence of rapid stellar rotation on the mass-loss, chemical enrichment, and evolution of massive stars. This helps us to understand the evolution of (rotating) massive stars and the formation of disks and rings out of their ejected wind material. Such studies may help find the evolutionary link between individual well-known groups of evolved massive stars like the luminous blue variables, red supergiants, yellow hypergiants, and B[e] supergiants.

Another recent addition to the working group's research interest is the studies of white dwarf stars. White dwarfs are the final evolutionary products for the majority of stars and, therefore, are critical in retracing the history of star formation in our Galaxy. Detailed studies of their properties also set the end boundary conditions for theoretical models of stellar evolution, containing phases of nuclear burning, mass-loss on the asymptotic giant branch, and the effect of binary interactions. White dwarfs are at the heart of cataclysmic events such as type Ia supernovae and a study of the double-degenerate population is essential to develop an understanding of these events. Spectroscopic data are obtained at observatories in Chile and United States, as well as with space-borne telescopes.

A significant research branch of the working group conducts numerical modelling of stellar atmospheres and winds with a focus on radiative transfer and hydrodynamics. Group members are authors of codes for NLTE modelling of stellar atmospheres, radiative transfer in expanding atmospheres, and radiative-hydrodynamical simulations of stellar winds. The stellar atmosphere code calculates spherically symmetric NLTE model atmospheres in hydrostatic and radiative equilibrium by simultaneously solving the equations of radiative transfer, hydrostatic equilibrium, radiative equilibrium, and statistical equilibrium. This code was developed from scratch. Radiative transfer codes are able to solve the radiative transfer equation in a moving multidimensional medium. The hydrodynamics code is able to simulate the evolution of a two-component radiatively driven stellar wind. Dynamics of poorly coupled stellar wind from hot stars remains a very challenging problem.

The working group is actively involved in the preparation of new standards of the Virtual Observatory (VO), mainly those focused on optical spectroscopy, and the development of new VO tools. This is organised at the national level as the Czech Virtual Observatory (CZVO) in close collaboration with the International Virtual Observatory Alliance. The main achievements of CZVO activities are the VO-compatible archive of stellar spectra obtained with the 2-m telescope (the echelle spectra from HEROS that are already publicly available have been added to the VO registers) and the web service VO-KOREL facilitating the Fourier disentangling of spectra in VO with the widely acknowledged procedure KOREL.

The working group (in collaboration with the working group 'High Energy Astrophysics') is also involved in the preparation of ground-based pre-launch spectroscopic supplementary observations and related data analysis connected with the Gaia satellite (ESA). This research is supported by a PECS project.
Last update 19.09.2010