Contributed Talk - Splinter Stellar

Thursday, 24 September 2020, 14:23   (virtual room M)

Observational evidence that binary interaction is always required to form hot subdwarf stars

Ingrid Pelisoli (1), J. Vos(1), S. Geier(1), V. Schaffenroth(1), A. Baran (2)
(1) Universit├Ąt Potsdam, (2) Pedagogical University of Krakow

Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed. If such formation scenarios without interaction were possible, that would also imply the existence of hot subdwarfs in wide binaries that are not predicted to interact. We probe the existence of these systems by analysing light curves from the Transiting Exoplanet Survey Satellite (TESS) for all known hot subdwarfs with a main sequence wide binary companion, and by searching for common proper motion pairs to spectroscopically confirmed hot subdwarfs. In this talk, I will present our results showing that (i) the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars, providing evidence of previous interaction causing spin-up, and (ii) there is a shortage of hot subdwarfs in common proper motion pairs, considering the frequency of such systems among progenitors. These results suggest that binary interaction is always required for the formation of hot subdwarfs.