Astron. Astrophys. 348, L25-L28 (1999)

Letter to the Editor

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

U. Heber ¹, I.N. Reid ² and K. Werner <sup>3

1</sup> Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstrasse 7, D-96049 Bamberg, Germany (heber@sternwarte.uni-erlangen.de)
² Palomar Observatory 105-24, California Institute of Technology, Pasadena, CA 91125, USA
³ Universität Tübingen, Institut für Astronomie und Astrophysik, D-72076 Tübingen, Germany

Received 16 June 1999 / Accepted 6 July 1999

Abstract

PG 1605+072 has unique pulsational properties amongst the members of the new class of pulsating sdB (EC 14026) stars. It has the longest periods and the richest, most puzzling frequency spectrum (55 periods). We present a quantitative analysis of a Keck HIRES spectrum using NLTE and LTE model atmospheres. Atmospheric parameters (, , ), metal abundances, and the rotational velocity are determined. He, C, N and O are subsolar as well as the intermediate mass elements Mg and Si, whereas Ne and Fe are solar. This abundance pattern is caused by diffusion. PG 1605+072 displays considerable line broadening probably caused by rotation (v sini = 39 km/s, P8.7h) and, therefore, is predicted to evolve into an unusually fast rotating white dwarf. Unequal rotational splitting may explain its puzzling pulsation pattern. The solar Fe abundance and the rapid rotation nicely confirms recent predictions of diffusion/pulsation models.

Key words: stars: abundances stars: atmospheres stars: horizontal-branch stars: individual: PG 1605+072 stars: oscillations stars: rotation

* Based on observations obtained at the W.M. Keck Observatory, which is operated by the Californian Association for Research in Astronomy for the California Institute of Technology and the University of California
** based on observations collected at the ESO Southern Observatory

Send offprint requests to: U. Heber

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999

helpdesk.link@springer.de