Discovery and analysis of a hydrogen-rich PG 1159 star

The discovery of a new peculiar PG 1159 star by follow-up spectroscopy of candidates selected from objective-prism plates of the Hamburg Schmidt Survey is presented. From a NLTE model atmosphere analysis an effective temperature of 130 000 +/- 10 000 K and a surface gravity of log g = 6.2 +/- 0.2 are determined, which together with the high carbon abundance place HS 2324+3944 in the region of low gravity PG 1159 stars. The detection of hydrogen, however, makes HS 2324+3944 unique amongst the PG 1159 stars. While three central stars of Planetary Nebulae have spectra similar to HS 2324+3944, hydrogen could not be detected up to now in any PG 1159 star not associated with a nebula. The abundances of helium, carbon and nitrogen (C/He=0.3, N/He< 2 . 10-3) are similar to that of ''normal'' PG 1159 stars while the O abundance is found to be somewhat lower than ''normal'' (O/He=2-10 . 10-3).