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Title: High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances

Abstract

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, anmore » important datum for determinations of their relative ages. {copyright} {ital 1996 The American Astronomical Society.}« less

Authors:
 [1];  [2];  [3];  [4]
  1. Lawrence Livermore National Laboratory, MS L-413, P.O. Box 808, Livermore, California 94550 (United States)
  2. University of California Observatories, Lick Observatory, Santa Cruz, California 95064 (United States)
  3. Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
  4. Observatorio Astronomico, Laprida 854, 500 Cordoba (Argentina)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
OSTI Identifier:
467178
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 470; Journal Issue: 2; Other Information: PBD: Oct 1996
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; STAR CLUSTERS; RED GIANT STARS; AGE ESTIMATION; ELEMENT ABUNDANCE; OXYGEN; SODIUM; SPATIAL DISTRIBUTION; SPECTRA

Citation Formats

Minniti, D, European Southern Observatory, D-85748 Garching bei Muenchen, Peterson, R C, Geisler, D, and Claria, J J. High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances. United States: N. p., 1996. Web. doi:10.1086/177921.
Minniti, D, European Southern Observatory, D-85748 Garching bei Muenchen, Peterson, R C, Geisler, D, & Claria, J J. High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances. United States. https://doi.org/10.1086/177921
Minniti, D, European Southern Observatory, D-85748 Garching bei Muenchen, Peterson, R C, Geisler, D, and Claria, J J. 1996. "High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances". United States. https://doi.org/10.1086/177921.
@article{osti_467178,
title = {High-dispersion spectroscopy of giants in metal-poor globular clusters. II. Oxygen and sodium abundances},
author = {Minniti, D and European Southern Observatory, D-85748 Garching bei Muenchen and Peterson, R C and Geisler, D and Claria, J J},
abstractNote = {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.}},
doi = {10.1086/177921},
url = {https://www.osti.gov/biblio/467178}, journal = {Astrophysical Journal},
number = 2,
volume = 470,
place = {United States},
year = {Tue Oct 01 00:00:00 EDT 1996},
month = {Tue Oct 01 00:00:00 EDT 1996}
}