Abstract

Contributed Talk - Splinter CloseBinaries   (MW-0250)

Discovery of a composite sdB binary with a strongly active K-type companion

U. Heber (1), A.Gebhardt(1), L.Kufleitner(1), S. Geier(2), M.Dorsch(2), A. Bhat(2), F. Mattig(2),V. Schaffenroth (3)
(1) FAU Erlangen-Nürnberg, (2) Uni Potsdam,(3) TLS, Tautenburg

We report the discovery of rotational modulation in the TESS light curve (30 min. cadence) of the composite sdB+K binary TIC96520292 resulting from star spots on the surface of the companion. In addition, two strong flares lasting for a few hours were recorded, indicating magnetic activity. High resolution (UVES) spectra reveal strong chromospheric emission in the Calcium H and K lines as well as in the Ca NIR triplet. The atmospheric parameters were determined from UVES spectra for both stars. The atmospheric parameters of the hot subdwarf are typical for sdB stars. The companion is a normal composition rapidly rotating K1V star. An analysis of the spectral energy distribution allowed us to determine the angular diameter, the surface ratio of the components, the effective temperature of the companion as well as the interstellar reddening. Gaia's precise parallax is used to derive the radii and luminosities of both stars. While two similar binaries have been discovered from TESS short cadence (2 min.) light curves before, the activity and flares of TIC96520292 are extraordinally strong.