Four new subdwarf B pulsators

• Published in: Astronomy and astrophysics (Berlin) 2001-11, Vol.378 (2), p.466-476
• Main Authors: Østensen, R., Heber, U., Silvotti, R., Solheim, J. E., Dreizler, S., Edelmann, H.
• Format: Article
• Language: English
• Subjects: HS 0444+0408; HS 1824+5745; HS 2151+0857; stars: individual: HS 0039+4302; stars: oscillations; subdwarfs
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20011218

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.