Bibcode
García López, R. J.; Israelian, G.; Rebolo, R.; Bonifacio, P.; Molaro, P.; Basri, G.; Shchukina, N.
Bibliographical reference
New Astronomy Reviews, Volume 45, Issue 8, p. 519-523.
Advertised on:
7
2001
Journal
Citations
5
Refereed citations
5
Description
Oxygen abundances have been derived in a sample of very metal-poor stars
from observations of the Oi triplet at /λλ 7771-5 Å
and OH lines in the near UV. Iron abundances derived in LTE were
corrected for NLTE effects following Thévenin and Idiart [ApJ 521
(1999) 753]. Furthermore, a detailed NLTE analysis of iron lines has
been carried out for one of the observed stars, BD +23/° 3130
([Fe/H]NLTE=-2.43), providing consistent values of effective
temperature, surface gravity and metallicity, that are in good agreement
with independent estimates from the infrared flux method, Hipparcos
parallaxes and recent NLTE work in the literature, respectively. These
parameters, especially the higher gravity obtained with respect to
previous analyses, reduce the discrepancies claimed by Fulbright and
Kraft [AJ 118 (1999) 527] between the oxygen abundances determined from
OH and [Oi] /λ 6300 Å lines, and give a similar abundance
from the Oi triplet for BD+23/° 3130. A mean value of the
oxygen-to-iron ratio [O/Fe]/=0.78+/-0.16 for this star is fully
consistent with the abundances derived from the three sets of features.
This consistency, which is found using 1D hydrostatic model atmospheres,
strongly constrains the effects predicted by 3D hydrodynamical models on
these three indicators. 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.