Astronomy and Astrophysics, volume 290, 897-905 (1994/10-3)
Abundance analysis of the hot post-AGB star Barnard 29.
CONLON E.S., DUFTON P.L. and KEENAN F.P.
Abstract (from CDS):
We present a model atmosphere analysis for the relatively bright (V∼13) globular cluster post-AGB star, Barnard 29, using IUE and high resolution (0.06A FWHM) optical spectra. The derived atmospheric parameters are Teff=20000±1000K and logg=3.0±0.1dex, which imply a current mass of ∼0.55M☉. The chemical composition provides important constraints on the post-AGB evolutionary stage. We find an overall metal deficiency of 1.46±0.11dex, which is compatible with the mean [Fe/H] obtained from previous M13 studies. The most interesting feature is the severe carbon deficiency of more than 2.0dex which has also been observed in a number of high latitude B-type low gravity stars. Hence the present results supports the recent classification of these objects as hot post-AGB stars. Relative to the overall metallicity, the observed carbon deficiency of Barnard 29 coupled with a significant nitrogen overabundance indicates that this star has left the AGB before the third dredge-up has occurred. The implications for AGB and post-AGB evolution are briefly discussed.