A search for close binary systems in the SALT survey of hydrogen-deficient stars using {\it TESS}

TL;DR

This study used TESS data to search for short-period variability in hydrogen-deficient stars from the SALT survey, identifying one confirmed close binary and analyzing the binary fraction among different subtypes.

Contribution

It provides the first systematic search for close binaries in hydrogen-deficient stars using TESS, revealing the binary fraction and characterizing variability causes.

Findings

One confirmed close binary system (Ton S 415) identified.

Close binary fraction is approximately 3.5% among intermediate helium hot subdwarfs.

No close binaries found among extreme helium subdwarfs.

Abstract

The {\it TESS} periodograms of the SALT survey catalogue of hydrogen-deficient stars were searched for evidence of short-period variability. Periodic light curve variations were identified in 16 stars out of 153 catalogue objects, of which 10 were false positives. From the remaining 6 identified variables, Ton S 415 is a known close binary system and the sixth close binary containing a hydrogen-deficient hot subdwarf. Radial velocity and SED analyses ruled out the remaining 5 as close binary systems; the causes of their variability remain uncertain. With one or more K-type companions, BPS CS 22956-0094 may be a wide binary or triple. From this SALT+{\it TESS} sample, the fraction of close binaries stands at $ 1/29 \approx 3.5\%$ for intermediate helium hot subdwarfs and $0/124 = 0\%$ for extreme helium subdwarfs.