Detection of pulsations in three subdwarf B stars ^*,**

¹ Institutt for Fysikk, Universitetet i Tromsø, 9037 Tromsø, Norway e-mail: janerik@phys.uit.no
² Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, 96049 Bamberg, Germany e-mail: ai03@sternwarte.uni-erlangen.de; edelmann@sternwarte.uni-erlangen.de
³ Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: silvotti@na.astro.it
⁴ Institut für Astronomie und Astrophysik, Waldhäuser Straße 64, 72076 Tübingen, Germany e-mail: dreizler@astro.uni-tuebingen.de

Corresponding author: R. Østensen, roy@phys.uit.no

Received: 10 August 2000
Accepted: 5 December 2000

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.