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Oxygen abundances in metal-poor subgiants

Published online by Cambridge University Press:  23 December 2005

A.E. García Pérez
Affiliation:
Institute for Astronomy and Space Physics, Box 515 SE-751 20 Uppsala, Sweden email: aegp@astro.uu.es, email: bg@astro.uu.se Present address: Department of Physics and Astronomy, The Open University, Walton Hall, MK7 6AA, UK email: a.e.garcia-perez@open.ac.uk.
M. Asplund
Affiliation:
Mt. Stromlo Observatory, Cotter Rd., Weston, ACT 2611, Australia email: martin@mso.anu.edu.au
F. Primas
Affiliation:
European Southern Observatory, Karl-Schwarzschild Str. 2, D-85748 Garching b. München, Germany email: fprimas@eso.org
P.E. Nissen
Affiliation:
Department of Physics and Astronomy, University of Århus, DK-8000 Århus C, Denmark email: pen@phys.au.dk
B. Gustafsson
Affiliation:
Institute for Astronomy and Space Physics, Box 515 SE-751 20 Uppsala, Sweden email: aegp@astro.uu.es, email: bg@astro.uu.se
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Abstract

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There seems to be no consensus on the [O/Fe] values found in metal-poor stars nor their trend with metallicity: different indicators give different results. We present here [O/Fe] derived from three different oxygen abundance indicators ([OI], OI and OH UV lines) for a sample of thirteen subgiant stars with metallicities in the range $-3\le\mathrm{[Fe/H]\le-1.5$. Oxygen and iron abundances were determined from the analysis of high $S/N$ spectra acquired with the UVES spectrograph at VLT. We found good agreement between [O/Fe] estimates based on OH and the estimates based on [Oi] ($\mathrm{mean\ difference}\sim-0.09\pm0.25(\mathrm{s.d.})$), although the scatter is not insignificant. Unfortunately, good agreement is not reached for the third indicator ($\mathrm{mean\difference}\sim0.19\pm0.22(\mathrm{s.d.})$). Our [OI] and OH-based estimates do not show a well defined linear trend with metallicity. Another interesting result is that the abundances based on molecular lines ($\mathrm{[O/Fe]}\sim0.45$) are in general lower than previous published results for turn-off stars even though a lower solar oxygen abundance ($A(\mathrm{O})=8.74$) was assumed.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union