2008/01/04 by Kim A. Venn, K. A. Venn, David L. Lambert +1 · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/529069
Accepted for ApJ. 17 pages, 10 figures
arxiv created 2008/01/04 · openalex publication_date 2008/04/04 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
Chemically peculiar stars define a class of stars that show unusual elemental abundances due to stellar photospheric effects and not due to natal variations. In this paper, we compare the elemental abundance patterns of the ultra-metal-poor stars with metallicities [ Fe/H ] ∼ − 5 to those of a subclass of chemically peculiar stars. These include post-AGB stars, RV Tauri variable stars, and the Lambda Bootis stars, which range in mass, age, binarity, and evolutionary status, yet can have iron abundance determinations as low as [ Fe/H ] ∼ − 5. These chemical peculiarities are interpreted as due to the separation of gas and dust beyond the stellar surface, followed by the accretion of dust-depleted gas. Contrary to this, the elemental abundances in the ultra-metal-poor stars are thought to represent yields of the most metal-poor supernovae and, therefore, observationally constrain the earliest stages of chemical evolution in the universe. Detailed chemical abundances are now available for HE 1327–2326 and HE 0107–5240, the two extreme ultra-metal-poor stars in our Galaxy, and for HE 0557–4840, another ultra-metal-poor star found by the Hamburg/ESO survey. There are interesting similarities in their abundance ratios to those of the chemically peculiar stars; e.g., the abundances of the elements in their photospheres are related to the condensation temperature of that element. If these three stars are chemically peculiar, then their CNO abundances suggest true metallicities of [ X/H ] ∼ − 2 to –4. It is important to establish the nature of these stars, since they are used as tests of the early chemical evolution of the Galaxy.