EDP Sciences
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Volume 415, Number 2, February IV 2004
Page(s) 559 - 569
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20034616

A&A 415, 559-569 (2004)
DOI: 10.1051/0004-6361:20034616

On the Galactic chemical evolution of sulfur

N. Ryde1, 2 and D. L. Lambert2

1  Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
2  Department of Astronomy, University of Texas, Austin, TX 78712-1083, USA

(Received 21 May 2003 / Accepted 12 November 2003 )

Sulfur abundances have been determined for ten stars to resolve a debate in the literature on the Galactic chemical evolution of sulfur in the halo phase of the Milky Way. Our analysis is based on observations of the S I lines at 9212.9, 9228.1, and 9237.5 Å for stars for which the S abundance was obtained previously from much weaker S I lines at 8694.0 and 8694.6 Å. In contrast to the previous results showing [S/Fe] to rise steadily with decreasing [Fe/H], our results show that [S/Fe] is approximately constant for metal-poor stars ( $\rm [Fe/H]\la -1$) at $\rm [S/Fe] \simeq +0.3$. Thus, sulfur behaves in a similar way to the other  $\alpha$ elements, with an approximately constant [S/Fe] for metallicities lower than ${\rm [Fe/H]}\simeq -1$. We suggest that the reason for the earlier claims of a rise of [S/Fe] is partly due to the use of the weak S I  8694.0 and 8694.6 Å lines and partly uncertainties in the determination of the metallicity when using Fe I lines. The S I  9212.9, 9228.1, and 9237.5 Å lines are preferred for an abundance analysis of sulfur for metal-poor stars.

Key words: stars: abundances -- stars: atmospheres -- stars: population II -- Galaxy: abundances -- Galaxy: evolution -- Galaxy: halo

Offprint request: N. Ryde, ryde@astro.uu.se

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