High-resolution Keck I spectroscopy of Galactic halo post-asymptotic giant branch stars
Abstract
Absolute and differential abundance analyses have been performed from high-resolution, high signal-to-noise ratio optical (Keck I) spectra for three evolved Galactic halo stars, namely PG 1704 + 222, HD 341617 and LS IV -04 01. Their derived atmospheric parameters indicate that all three objects are undergoing a post-asymptotic giant branch (post-AGB) phase of evolution. A differential abundance analysis reveals HD 341617 as having a mild carbon deficiency of 0.74 dex, possibly due to the star having evolved off the AGB before the onset of the third dredge-up. Although such carbon underabundances are typical of hot post-AGB objects, the same trend is not observed in PG 1704 + 222, where the carbon abundance is found to be consistent with those derived for nitrogen and oxygen. Hence, a dredge-up scenario need not be invoked to explain the chemical composition of PG 1704 + 222. For LS IV -04 01 no iron deficiency is apparent relative to magnesium and silicon, and hence a gas-dust separation event in the AGB progenitor need not be invoked for this star.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2002
- DOI:
- 10.1046/j.1365-8711.2002.05912.x
- Bibcode:
- 2002MNRAS.337..851M
- Keywords:
-
- stars: abundances;
- stars: AGB and post-AGB;
- stars: early-type;
- stars: Population II