Invited Talk - Plenary
The impact of TESS on our understanding of compact binary stars
More than half of all stars are found to be not in single but in binary or even multiple systems. A significant number of them will influence each other during their lifetime. This is happening mostly via mass transfer from one star to the other. This mass transfer can be stable or unstable. An unstable mass transfer leads to a common envelope around both stars resulting in a very compact binary system. This very short-lived phase is still poorly understood and for a better understanding compact binary systems, which evolved through this phase, have to be studied. About a third of the hot subdwarfs of spectral type B, which are core-helium burning stars stripped of most of their envelope on the red giant branch, are found in compact binaries with cool, low-mass stellar, substellar or white dwarf companions with periods from about one hour to a few days. Investigations show that binary interaction is required for the formation of a hot subdwarf, which makes them ideal for studying mass transfer in binaries. The most compact hot subdwarf binaries must have gone through a previous common-envelope phase. Those compact binaries show different kinds of variations in their light curves, which can be used to characterize the primary star and its companion. Many hot subdwarfs have space-based light curves with high signal-to-noise ratio available now. We used the light curves from Transiting Exoplanet Survey Satellite (TESS) to look for more compact sdB binaries and to derive their orbital and fundamental parameters. In this talk I will present the results of our study of close hot subdwarf binaries with TESS light curves constraining their period and mass distributions as well as the nature of their companions for the first time and increasing the sample of studied post-common envelope systems significantly.