Open AccessHigh‐resolution Keck I spectroscopy of Galactic halo post‐asymptotic giant branch stars
Author(s) -
Mooney C. J.,
Rolleston W. R. J.,
Keenan F. P.,
Dufton P. L.,
Ryans R. S. I.,
Aller L. H.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05912.x
Subject(s) - physics , asymptotic giant branch , astrophysics , stars , astronomy , halo , red giant , carbon star , galactic halo , giant star , galaxy
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.