Astronomy & Astrophysics

Free access article

Issue		A&A Volume 368, Number 1, March II 2001
Page(s)		175 - 182
Section		Formation, structure and evolution of stars
DOI		10.1051/0004-6361:20000488

A&A 368, 175-182 (2001)
DOI: 10.1051/0004-6361:20000488

Detection of pulsations in three subdwarf B stars

R. Østensen¹, J.-E. Solheim¹, U. Heber², R. Silvotti³, S. Dreizler⁴ and H. Edelmann²

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

(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 $\sim$ 126 s; A $\sim$ 7 mma) and two short periods are seen for HS 2149+0847 (P $\sim$ 142, 159 s; A $\sim$ 11, 7 mma), whereas the single oscillation detected for HS 2201+2610 has a considerably longer period (P $\sim$ 350 s; A $\sim$ 11 mma). Our NLTE model atmosphere analysis of the time-averaged optical spectra indicate that HS 0815+4243 has $T_{\rm eff}$ = 33 700 K and ${\rm log} g=5.95$ , HS 2149+0847 has $T_{\rm eff} = 35 600$ K and log g = 5.9, and HS 2201+2610 has $T_{\rm eff}$ = 29 300 K and log g= 5.4. This places the former two at the hot end and the latter at the cool end of the theoretical sdBV instability strip.

Key words: subdwarfs -- stars: oscillations -- stars: individual: HS 0815+4243 HS 2149+0847 HS 2201+2610

Offprint request: R. Østensen, roy@phys.uit.no

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