THE EC-14026 STARS - VII - PG-1605+072, A STAR WITH MANY PULSATION MODES

We report the discovery of large-amplitude ( similar to 0.25 mag) puls ations in the bright (V = 12.8) sdB star, PG 1605 +/- 072, The dominan t period is 480 s, but more than 20 periods were present on at least t hree separate occasions. Frequency analysis of the complete data set y ields more than 30 periods. A few of these are harmonics or linear com binations of the strongest modes, Excluding the latter, the periods sp an a range of almost 400 s, which contrasts with the typical range < 2 0 s for most other EC 14026 stars. Analysis of multicolour photometry limited any cool companion to being a main-sequence star of type MO or later. Balmer line profile fitting yielded an effective temperature o f 32100 +/- 1000 K and a log g of 5.25 +/- 0.10, significantly smaller than in the other stars of the EC 14026 class, and possibly indicativ e of a more evolved state. The lower gravity is probably responsible f or 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 multi longitude photometric campaign.