2M0415+0154: a new bright, short-period subdwarf B pulsator^*

¹ Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: [raquel;roy]@ster.kuleuven.be
² Steward Observatory, University of Arizona, Tucson, AZ 85721, USA e-mail: bgreen@as.arizona.edu
³ Dr. Remeis-Sternwarte, Sternwartstr. 7, 96049 Bamberg, Germany e-mail: geier@sternwarte.uni-erlangen.de

Received: 21 November 2008
Accepted: 28 January 2009

Abstract

Context. The discovery of stellar oscillations in some subdwarf B stars presents the opportunity of studying the interior structure of these objects, thereby clarifying their possible formation channels.

Aims. Our ongoing survey attempts to increase the number of pulsating hot subdwarfs to better understand the complexities of the various subgroups within the population of pulsators and to identify targets suitable for seismological analysis.

Methods. Light curves for a list of potential pulsators were obtained at the Nordic Optical Telescope. The candidates were mainly selected based on similar  and  as known pulsators. A frequency analysis of the light curves was performed to investigate the multiperiodic photometric variability.

Results. From the sample we surveyed in 2007, 2M0415+0154 was the only star clearly showing photometric modulations. Follow-up photometry revealed three clear pulsation modes with periods between 143 and 150 s. Additional spectroscopic data was taken on 2M0415+0154 to refine its physical parameters. We find  = 34 0000 K,  =  dex, , which are typical of sdB pulsators in this period range. No evidence of a companion was found.

Conclusions. A new short-period sdB star has been discovered, 2M0415+0154. Its physical parameters and oscillation frequencies agree with those of other V361 Hya stars. The relative brightness and simple frequency spectrum of this star make it a suitable target for empirical mode identification, essential for a seismological analysis of simple pulsators.