Long-term EXOTIME photometry and follow-up spectroscopy of the sdB pulsator HS 0702+6043

Abstract

Pulsating subdwarf B (sdB) stars oscillate in short-period p-modes or long-period g-modes. HS0702+6043 (DW Lyn) is one of a few objects to show characteristics of both types and is hence classified as hybrid pulsator. It is one of our targets in the EXOTIME program to search for planetary companions around extreme horizontal branch objects. In addition to the standard exercise in asteroseismology to probe the instantaneous inner structure of a star, measured changes in the pulsation frequencies as derived from an O-C diagram can be compared to theoretical evolutionary timescales. Based on the photometric data available so far, we are able to derive a high-resolution frequency spectrum and to report on our efforts to construct a multi-season O-C diagram. Additionally, we have gathered time-resolved spectroscopic data in order to constrain stellar parameters and to derive mode parameters as well as radial and rotational velocities.