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arXiv · 2211.03598

TESS uncloaks the secondaries in hydrogen-deficient binaries

C. Simon Jeffery
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Abstract

$\upsilon$ 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 $\upsilon$ 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.

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C. Simon Jeffery. 2022-11-07. TESS uncloaks the secondaries in hydrogen-deficient binaries. https://doi.org/10.1093/mnrasl%2Fslac140

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