In a long-term project we have followed-up spectroscopically on hot subdwarf candidates from the "Palomar-Green Catalogue of Ultraviolet Excess Stellar Objects" (Green et al., 1986). While most objects turned out to be hot subluminous stars (Moehler et al., 1990b, Theissen et al., 1993) or blue horizontal branch stars (Schmidt et al., 1992) a few candidates showed surface gravities too low for such stars and more typical for giant stars. In addition these objects exhibit normal helium line strengths, again in contrast to the usually helium weak-lined hot subdwarfs.
The normality of the H/He spectrum might indicate that these stars are normal, i.e. massive giants in a strange place, very far from the galactic disk. In this case they were either created in the disk and thrown out (cf. Leonard, 1991) or they were born in the halo (which could be explained by the model of the "galactic fountain", Dyson & Hartquist, 1983). On the other hand, such stars could be post-AGB stars on their way from the asymptotic giant branch (AGB) to the white dwarf domain that spectroscopically mimic massive stars. Since this part of the evolution proceeds very fast (104 years, Schönberner, 1983), such objects should be rather rare. Indeed, not many have been found and analysed so far (Conlon et al., 1991, 1993a).
Since a metallicity analysis offers a good possibility to distinguish between young, massive OB stars and post-AGB stars we decided to get higher resolution (about 1 Å) spectra of some of these stars. Here we report the results for two objects, PG 1323-086 and PG 1704+222. Lower resolution spectra of PG 1704+222 have already been discussed by Conlon et al. (1993a). In addition to these stars we observed spectra of well known and analysed main-sequence and sub-giant OB stars to allow direct comparisons between the spectra. In Sect. 2 we describe the observations and the reduction of the data. Sects. 3 and 4 describe the determination of atmospheric parameters and abundances. Sect. 5 gives the kinematic data of the stars, while Sect. 6 gives a discussion of the results.
© European Southern Observatory (ESO) 1998
Online publication: June 26, 1998