A survey for pulsating subdwarf B stars with the Nordic Optical Telescope ^*

¹ Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: [roy;raquel]@ster.kuleuven.be
² Institutt for Teoretisk Astrofysikk, Universitetet i Oslo, 0212 Blindern-Oslo, Norway
³ Dr. Remeis-Sternwarte, Astronomisches Institut der Univ. Erlangen-Nürnberg, 96049 Bamberg, Germany
⁴ INAF-Osservatorio Astronomico di Torino, Strada dell'Osservatorio 20, 10025 Pino Torinese, Italy
⁵ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁶ Departemento Física Aplicada, Universidade de Vigo, 36310 Vigo, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁸ Laboratoire d'Astrophysique de Toulouse-Tarbes, Univ. de Toulouse, 14 Av. Edouard Belin, 31400 Toulouse, France
⁹ Nordic Optical Telescope, 38700 Santa Cruz de La Palma, Spain

Received: 15 October 2009
Accepted: 6 January 2010

Abstract

Context. A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009.

Aims. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars.

Methods. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations.

Results. In total twenty new pulsators were found in this survey, most of which have already been published and some extensively studied. We present four new short period pulsators, bringing the total of such pulsators up to 49. We also give limits on pulsation amplitudes for 285 objects with no obvious periodic variations, summarise the results of the survey, and provide improved physical parameters on the composite pulsators for which only preliminary estimates were published earlier.