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TwitterA&A 415, 155-170 (2004)
DOI: 10.1051/0004-6361:20031655
Oxygen trends in the Galactic thin and thick disks
T. Bensby, S. Feltzing and I. LundströmLund Observatory, Box 43, 221 00 Lund, Sweden
(Received 21 July 2003 / Accepted 24 October 2003)
Abstract
We present oxygen abundances for 72 F and G dwarf stars in the solar
neighbourhood. Using the kinematics of the stars we divide them into two
sub-samples with space velocities that are typical for the thick and thin
disks, respectively. The metallicities of the stars range from
[Fe/H]
-0.9 to
+0.4 and we use the derived oxygen abundances
of the stars to:
(1) perform a differential study of the oxygen trends in the thin
and the thick disk;
(2) to follow the trend of oxygen in the thin disk to the highest
metallicities.
We analyze the forbidden oxygen lines at 6300 Å
and 6363 Å as well as the (NLTE afflicted) triplet lines around
7774 Å. For the forbidden line at 6300 Å we have spectra of very high
S/N (
>400) and resolution (
R
215 000). This has enabled a
very accurate modeling of the oxygen line and the blending Ni lines. The high
internal accuracy in our determination of the oxygen abundances from this line
is reflected in the very tight trends we find for oxygen relative to iron.
From these abundances we are able to draw the following major conclusions:
(i) That the [O/Fe] trend at super-solar [Fe/H] continues downward which is in
concordance with models of Galactic chemical evolution. This is not seen
in previous studies as it has not been possible to take the blending Ni lines
in the forbidden oxygen line at 6300 Å properly into account;
(ii) That the oxygen trends in the thin and the thick disks are distinctly
different. This confirms and extends previous studies of the other
-elements;
(iii) That oxygen does not follow Mg at super-solar metallicities;
(iv) We also provide an empirical NLTE correction for the infrared
triplet that could be used for dwarf star spectra with a
S/N such that only
the triplet lines can be analyzed well, e.g. stars at large distances;
(v) Finally, we find that Gratton et al. (1999) overestimate the
NLTE corrections for the permitted oxygen triplet lines at ~7774 Å
for the parameter space that our stars span.
Key words: stars: fundamental parameters -- stars: abundances -- galaxy: disk -- galaxy: formation -- galaxy: abundances -- galaxy: kinematics and dynamics
Offprint request: T. Bensby, thomas@astro.lu.se
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