Spectral analysis of the multi mode pulsating subluminous B star PG 1605+072

PG 1605+072 has unique pulsational properties amongst the members of the ne w class of pulsating sdB (EC 14026) stars. It has the longest periods and t he richest, most puzzling frequency spectrum (55 periods). We present a qua ntitative analysis of a Keck HIRES spectrum using NLTE and LTE model atmosp heres. Atmospheric parameters (T-eff, log g. log n(He)/n(H)), metal abundan ces, and the rotational velocity are determined. He, C, N and O are subsola r as well as the intermediate mass elements Mg and Si, whereas Ne and Fe ar e solar. This abundance pattern is caused by diffusion. PG 1605+072 display s considerable line broadening probably caused by rotation (v sini = 39 km/ s, P<8.7h) and, therefore, is predicted to evolve into an unusually fast ro tating white dwarf. Unequal rotational splitting may explain its puzzling p ulsation pattern. The solar Fe abundance and the rapid rotation nicely conf irms recent predictions of diffusion/pulsation models.