The EC 14026 stars - VII. PG 1605+072, a star with many pulsation modes

Abstract

We report the discovery of large-amplitude (~0.25 mag) pulsations in the bright (V=12.8) sdB star, PG 1605+072. The dominant period is 480s, but more than 20 periods were present on at least three separate occasions. Frequency analysis of the complete data set yields more than 30 periods. A few of these are harmonics or linear combinations of the strongest modes. Excluding the latter, the periods span a range of almost 400s, which contrasts with the typical range <20s for most other EC 14026 stars. Analysis of multicolour photometry limited any cool companion to being a main-sequence star of type M0 or later. Balmer line profile fitting yielded an effective temperature of 32 100+/-1000K and a log g of 5.25+/-0.10, significantly smaller than in the other stars of the EC 14026 class, and possibly indicative of a more evolved state. The lower gravity is probably responsible for the fact that the pulsation periods and amplitudes are respectively much longer and larger than in other stars of the class. This star is an obvious target for asteroseismological investigation using a multilongitude photometric campaign.