TESS uncloaks the secondaries in hydrogen-deficient binaries

C. Simon Jeffery

Submitted on 7 November 2022


υ Sgr is the prototype of four known hydrogen-deficient binary (HdB) systems. These are characterised by a hydrogen-deficient A-type primary, variable hydrogen emission lines, and a normally unseen secondary presumed to be an upper main-sequence star. Orbital periods range from tens of days to 360 d. TESS observations of all four HdBs show a flux variation with well-defined period in the range 0.5 -- 0.9 d, too short to be associated with the supergiant primary, and more likely to be the rotation period of the secondary and associated with a chemical surface asymmetry or a low-order non-radial oscillation. The observed rotation period supports a recent analysis of the υ Sgr secondary. The observations give a direct glimpse of the secondary in all four systems, and should help to explain how the primary has been stripped to become a low-mass hydrogen remnant.


Comment: MNRAS: Accepted 2022 November 05. Submitted 2022 October 22, 5 pages

Subject: Astrophysics - Solar and Stellar Astrophysics