2017MNRAS.467.3963K

EC 03089-6421, classified sdO in the Edinburgh-Cape (EC) blue object survey, is shown to have unusually rapid pulsations with a dominant frequency near 32 mHz (amplitude ∼0.02 mag; period 31.1 s) - which appears to be strongly variable in amplitude on time-scales of hours and days - and a generally weaker frequency near 29 mHz (amplitude ∼0.004 mag; period 34.2 s), which is also variable in amplitude. This star varies at twice the frequency of any known hot subdwarf pulsator. Although the low-resolution EC spectrogram appears very similar to those of DAO stars, our analysis derives T_eff = 40 200 ± 1600 K; log g = 6.25 ± 0.23 and log N(He)/N(H) = -1.63 ± 0.55; more recent spectrograms give T_eff = 37 400 ± 1000 K; log g = 5.70 ± 0.13 and log N(He)/N(H) = -2.02 ± 0.17, both of which indicate that the gravity is too low for a white dwarf star, although the low temperature derived from the Balmer lines is at odds with the absence of neutral Helium and the strength of He II 4686. It is possible that EC 03089-6421 is a field analogue of the ω Cen sdO variables.