2019MNRAS.485.4330K

We present new results for hot subdwarf stars from the Edinburgh-Cape (EC) blue object survey. EC 03089-6421, an sdO star recently discovered to be a very rapid pulsator with periods near 31.1 and 34.2 s (29.2 and 32.1 mHz), is shown to have an even faster pulsation near 26.6 s (37.6 mHz) although all pulsations are variable in amplitude and effectively disappear in one of our runs. Five stars are discovered to be of the rapidly-pulsating (sdBV_r) type: EC 01441-6605, EC 10834-1301, EC 11275-2504, EC 11545-1459, and EC 21281-5010 each exhibit between one and three variations in the range 2-3 min (∼8.2-6.4 mHz) and are therefore p-mode pulsators. EC 15061-1442 shows a large-amplitude variation with a period ∼0.075 d if the star is a reflection effect binary and 0.15 d if an ellipsoidal variable. No eclipses are detected. Low-resolution EC survey classification spectroscopy is combined with published photometry from GALEX, WISE, and 2MASS and parallaxes from GAIA to derive, where possible, fundamental stellar parameters. The sdBV_r stars have T_eff in the range 34 000-45 000 K and log g between 5.0 and 5.6 consistent with p-mode pulsators. Derived stellar masses and radii are in the ranges 0.15-0.4 M_☉ and 0.15-0.2 R_☉. The sdOV star, EC 03089-6421 is found to have T_eff = 52 000 ± 3000 K and log g = 5.6 ± 0.2, and with a mass ∼0.1 M_☉ could be a progenitor to an extremely low-mass white dwarf.