Detection of pulsations in three subdwarf B stars

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Abstract
We report the detection of short period oscillations in the sdB stars HS 0815+4243, HS 2149+0847 and HS 2201+2610 from time-series photometry made at the Nordic Optical Telescope (NOT) from a sample of 31 candidates. Hence these three hot subdwarfs are new members of the EC 14026 class of pulsating sdB stars. One short period is detected for HS 0815+4243 (P ∼ 126 s; A ∼ 7 mma) and two short periods are seen for HS 2149+0847 (P ∼ 142, 159 s; A ∼ 11, 7 mma), whereas the single oscillation detected for HS 2201+2610 has a considerably longer period (P ∼ 350 s; A ∼ 11 mma). Our NLTE model atmosphere analysis of the time-averaged optical spectra indicate that HS 0815+4243 has T eff = 33 700 K and , HS 2149+0847 has K and log , and HS 2201+2610 has T eff = 29 300 K and log . This places the former two at the hot end and the latter at the cool end of the theoretical sdBV instability strip.