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: email@example.com
3 Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, 96049 Bamberg, Germany e-mail: firstname.lastname@example.org; email@example.com
4 Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy e-mail: firstname.lastname@example.org
5 Institut für Astronomie und Astrophysik, Waldhäuser Straße 64, 72076 Tübingen, Germany e-mail: email@example.com
Corresponding author: R. Østensen, firstname.lastname@example.org
Accepted: 28 August 2001
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 ( mma) and a second weaker pulsation at 170 s ( 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
Based on observations obtained at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.
Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Plank-Institute für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy.
© ESO, 2001