Balloon 090100001: A short and long period pulsating sdB star

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Spain e-mail: ror@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38200 La Laguna, Spain e-mail: fph@iac.es
³ Departamento de Física Aplicada, Universidade de Vigo, 36200 Vigo, Spain e-mail: ulla@uvigo.es
⁴ Instituto de Astrofísica de Andalucía, 18008 Granada, Spain e-mail: garrido@iaa.es
⁵ Isaac Newton Group of Telescopes, 37800 Santa Cruz de La Palma, Spain e-mail: roy@ing.iac.es
⁶ Department of Physics and Astronomy, University of Delaware, Newark, DE 1976, USA e-mail: jimmacd@udel.edu

Received: 11 January 2005
Accepted: 1 April 2005

Abstract

We report the discovery of long period oscillations in the light curve of the bright sdB pulsator Balloon 090100001. We find at least three peaks in the low frequency amplitude spectrum of the star (at periods 2733, 3665, 4378 s) and 10 certain frequencies in the short period range (118–356 s), but probably more than 25 frequencies modulate the light curve of this object. This star is one of only two sdBs, together with HS 0702+6043, known to show simultaneously short and long period pulsations. We also discuss the results of a set of multicolour photometric observations of the target, for which an amplitude-phase diagram is possible for the two dominant peaks. Comparision with theoretical models indicate that the short period peaks correspond to p modes clustered around the fundamental and the first three overtones, while the long period peaks correspond to g modes of high radial order.