Spectral analysis of O(He)-type post-AGB stars *
S. Dreizler 1 and
B. Wolff 2
Received 25 May 1998 / Accepted 17 July 1998
We present an analysis of two recently discovered, very hot hydrogen-deficient post-AGB stars of spectral type O(He), namely HS 1522+6615 and HS 2209+8229, by means of state-of-the-art NLTE model atmospheres based on new optical, UV, and X-ray observations.
In the spectra of HS 1522+6615 we discovered a variability of the line complex on a time scale of few days. We also report on the discovery of a ring structure in the planetary nebula K 1-27 which has an O(He)-type central star.
We discuss how the group of O(He) stars fits in our picture of hydrogen-deficient post-AGB stellar evolution.
Key words: stars: abundances stars: evolution stars: individual: HS 1522+6615 stars: individual: HS 2209+8229 stars: AGB and post-AGB planetary nebulae: individual: K 1-27
* Based on observations obtained at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy; collected at the European Southern Observatory, La Silla, Chile; on observations made with ROSAT, retrieved from the archive; and on observations made with the International Ultraviolet Explorer (IUE) and retrieved from the IUE Final Archive; this research has made use of the SIMBAD database, operated at CDS, Strasbourg, France
Send offprint requests to: T. Rauch, (email@example.com)
© European Southern Observatory (ESO) 1998
Online publication: September 14, 1998