High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances
- Lawrence Livermore National Laboratory, MS L-413, P.O. Box 808, Livermore, California 94550 (United States)
- University of California Observatories, Lick Observatory, Santa Cruz, California 95064 (United States)
- Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
- Observatorio Astronomico, Laprida 854, 500 Cordoba (Argentina)
Oxygen and sodium abundances or upper limits have been determined for 17 red giant members of the metal-poor Galactic globular clusters M68 (two stars), M30 (two stars), M15 (two stars), M55 (two stars), and NGC 6397 (five stars), as well as for the moderately metal-poor clusters NGC 4833 (one star), NGC 6144 (one star), and NGC 6752 (three stars). The behavior of [O/Fe] with respect to luminosity and metallicity is investigated. As found in previous works, the oxygen-to-iron ratios show an upper envelope, in agreement with the mean level of field halo stars of similar metallicities ([O/Fe]=+0.4{plus_minus}0.15). Moreover, as is true of the more metal-rich giants in globular clusters, about one-third of the stars do not have enhanced oxygen with respect to iron, in contrast to field giants of similar metallicity, which are almost invariably oxygen-rich. Several explanations for this deficiency are examined, including emission possibly associated with mass-loss filling in the oxygen lines and evolutionary mixing effects. In particular, the abundances of oxygen and sodium are seen to be anticorrelated, in agreement with previous results (Kraft {ital et} {ital al}. 1995). The enhancement of oxygen in these extremely metal-poor clusters appears similar to that of less metal-deficient clusters, an important datum for determinations of their relative ages. {copyright} {ital 1996 The American Astronomical Society.}
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 467178
- Journal Information:
- Astrophysical Journal, Vol. 470, Issue 2; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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