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Oxygen Abundances Derived from UV OH and O I IR Lines in Very Metal-Poor Stars

Published online by Cambridge University Press:  30 March 2016

Ramón J. García López ,
Garik Israelian ,
Rafael Rebolo ,
Piercarlo Bonifacio ,
Paolo Molaro ,
Gibor Basri  and
Natalya Shchukina
Ramón J. García López
Affiliation:
Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, E-38071 La Laguna, Tenerife, Spain
Garik Israelian
Affiliation:
Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
Rafael Rebolo
Affiliation:
Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain Consejo Superior de Investigaciones Científicas, Spain
Piercarlo Bonifacio
Affiliation:
Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34131 Trieste, Italy
Paolo Molaro
Affiliation:
Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34131 Trieste, Italy
Gibor Basri
Affiliation:
Astronomy Department, University of California, Berkeley, California94720, USA
Natalya Shchukina
Affiliation:
Main Astronomical Observatory, National Academy of Sciences, 03680 Kyiv-127, Ukraine

Abstract

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Oxygen abundances have been derived in a sample of very metal-poor stars using the O I triplet at λλ 7771-5 Å and OH lines in the near UV. A detailed NLTE analysis of iron lines has been carried out for one of the observed stars, BD +23° 3130, providing consistent values of effective temperature and surface gravity that are in very good agreement with independent estimates from the infrared flux method and Hipparcos parallaxes, respectively. These parameters, especially the higher gravity obtained with respect to previous analyses, reduce the discrepancies claimed between the oxygen abundances determined from OH, O I triplet and [O I] λ 6300 Å lines, and give consistent abundances to within 0.16 dex for BD +23° 3130 ([Fe/H]NLTE = −2.43). The oxygen abundances derived for this new sample confirm previous findings for a progressive linear increase in the oxygen-to-iron ratio with a slope −0.33 ± 0.02 (including NLTE corrections to the iron abundances for all the stars considered) from solar metallicity to [Fe/H]∼ −3, and [O/Fe] values as high as ∼ 1.1 for stars with [Fe/H]≾ −2.5. These results can be interpreted as evidence for oxygen overproduction in the very early epoch of the formation of the Galactic halo, possibly associated with supernova events with very massive progenitor stars.

Type
II. Joint Discussions
Information
Highlights of Astronomy , Volume 12: Highlights of Astronomy. As presented at the XXIVth General Assembly of the IAU, 2000 , 2002 , pp. 413 - 415
Copyright
Copyright © Astronomical Society of Pacific 2002

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