TESS 2-minute data of 3,278 known hot subdwarfs show no transiting planet candidate at 0.15-10 d, and the eclipses of FBS 0603+830 agree with a low-mass white-dwarf companion

Question: Do the public TESS 2-minute light curves of known hot subdwarfs contain transiting planets or unexplained eclipses, and which limits follow? Approach: We matched the 6,616 known hot subdwarfs of Culpan et al. (2022) to the TIC and found SPOC 2-minute data for 3,278 stars (sectors 1 to 107). We searched the first, middle and last sector of each star (8,061 light curves) with a box least-squares search for periods of 0.15 to 10 d and durations scaled to a hot subdwarf. We set thresholds with 400 inverted-flux control sectors, applied automated tests for variability, shape, single events, duration and repetition, inspected all survivors by eye, made difference images, and measured completeness with 800 injected transits. Results: No planet candidate remains. The 37 signals that passed the automated tests are pulsations, aliases of known eclipsing binaries, blends, noise, and two catalogued eclipsing binaries (TOI-464.01, a TFOPWG false positive, and FBS 0603+830). The search recovers known HW Vir-type systems such as HW Vir, AA Dor and PG 1336-018. For a star radius of 0.2 solar radii, the 95 % upper limits on the fraction of hot subdwarfs with a transiting body are 0.6 %, 1.9 % and 5.1 % for 8 to 15 Earth radii at 0.15-1, 1-3 and 3-10 d, and 1.7 % for 2 to 4 Earth radii at 0.15-1 d. In seven sectors, FBS 0603+830 (P = 0.2608475 d) shows a flat 16.6-min primary eclipse of 1.03 %, a secondary eclipse (companion light 2.2 +/- 0.4 ppt), ellipsoidal (1.37 +/- 0.13 ppt) and beaming (0.48 +/- 0.11 ppt) signals, and no reflection effect. With an sdB mass of 0.47 solar masses, these give a companion of about 0.24 solar masses and 0.019 solar radii (R2/R1 = 0.099) with a black-body temperature near 10,000 K. This agrees with a cool low-mass white dwarf and not with an M dwarf or brown dwarf. Limitations: At most three sectors per star were searched. The limits use a uniform 0.2 solar-radius star and the automated tests only. The FBS 0603+830 masses depend on the assumed sdB mass and beaming factor; a radial-velocity orbit is necessary to confirm them.

hot subdwarfs · sdB stars · TESS · transit search · box least squares · occurrence rate · injection-recovery · eclipsing binaries · white dwarf companion · Doppler beaming · ellipsoidal variation · FBS 0603+830 · TOI-464 · HW Vir · null result · post-red-giant planets