Synthetic photometry for non-radial pulsations in subdwarf B stars

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK e-mail: brc@arm.ac.uk
² Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
³ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Received: 10 May 2004
Accepted: 12 August 2004

Abstract

We describe a method for computing theoretical photometric amplitude ratios for a number of modes of nonradially pulsating subdwarf B stars in both SDSS and UBVR systems. In order to avoid costly solutions of the non-adiabatic non-radial pulsation equations, we have adopted the adiabatic approximation. We argue that this is a valid approach, at least for the V361 Hya stars, because observations show that the temperature perturbations dominate the radius perturbations in the flux variation. We find that for V361 Hya stars, low-degree () modes may be difficult to distinguish using optical photometry. However, the high degree modes () are relatively well separated and may be distinguished more easily. We have also computed the amplitude ratios for a number of modes in PG 1716+426 stars. For these stars, the amplitude ratios for low degree modes () are well resolved. For oscillations with periods ~40 min, higher-degree modes () may also be identified easily from their amplitude ratios. However for longer period oscillations, the  and the  modes approach the and  modes respectively.