A search for close binary systems in the SALT survey of hydrogen-deficient stars using <i>TESS</i>

The 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+TESS sample, the fraction of close binaries stands at 1/29 ≈ 3.5 % for intermediate helium hot subdwarfs and 0/124 = 0 % for extreme helium subdwarfs.