Four new subdwarf B pulsators

Free access article

Issue		A&A Volume 378, Number 2, November I 2001


Page(s)		466 - 476
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20011218

A&A 378, 466-476 (2001)
DOI: 10.1051/0004-6361:20011218

Four new subdwarf B pulsators

R. Østensen^{1, 2}, U. Heber³, R. Silvotti⁴, J.E. Solheim², S. Dreizler⁵ and H. Edelmann³

¹ Isaac Newton Group of Telescopes, 37800 Santa Cruz de La Palma, Canary Islands, Spain
² Institutt for Fysikk, Universitetet i Tromsø, 9037 Tromsø, Norway
    e-mail: janerik@phys.uit.no
³ Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, 96049 Bamberg, Germany
    e-mail: ai03@sternwarte.uni-erlangen.de; edelmann@sternwarte.uni-erlangen.de
⁴ Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
    e-mail: silvotti@na.astro.it
⁵ Institut für Astronomie und Astrophysik, Waldhäuser Straße 64, 72076 Tübingen, Germany
    e-mail: dreizler@astro.uni-tuebingen.de

(Received 13 June 2001 / Accepted 28 August 2001 )

Abstract
We report the detection of short period oscillations in the sdB stars HS 0039+4302, HS 0444+0408, HS 1824+5745 and HS 2151+0857 from time-series photometry made at the Nordic Optical Telescope (NOT) of a sample of 55 candidates. Hence these four hot subdwarfs are new members of the EC 14026 class of pulsating sdB stars. HS 0039+4302 is a multi-mode pulsator with at least four distinct periods in the range between 182 and 234 s, and amplitudes up to 8 mma. HS 0444+0408 shows one dominant pulsation at 137 s ( $A \sim 12$ mma) and a second weaker pulsation at 170 s ( $A \sim 3$ mma). For HS 1824+5745 we find a single period of 139 s with an amplitude of about 5 mma. HS 2151+0857 shows four periods in the range 129-151 s with amplitudes between 2 and 5 mma. Our NLTE model atmosphere analysis of the time-averaged optical spectra place all stars well within the theoretical sdBV instability strip.

Key words: subdwarfs -- stars: oscillations -- stars: individual: HS 0039+4302, HS 0444+0408, HS 1824+5745, HS 2151+0857

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

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