Sulphur and zinc abundances in Galactic stars and damped Lyα systems ^*,**

¹ Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China e-mail: cyq@bao.ac.cn
³ Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia e-mail: martin@mso.anu.edu.au
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK e-mail: pettini@ast.cam.ac.uk

Corresponding author: P. E. Nissen, pen@phys.au.dk

Received: 9 July 2003
Accepted: 19 November 2003

Abstract

High resolution spectra of 34 halo population dwarf and subgiant stars have been obtained with VLT/UVES and used to derive sulphur abundances from the and  lines. In addition, iron abundances have been determined from 19  lines and zinc abundances from the lines. The abundances are based on a classical 1D, LTE model atmosphere analysis, but effects of 3D hydrodynamical modelling on the [S/Fe], [Zn/Fe] and [S/Zn] ratios are shown to be small. We find that most halo stars with metallicities in the range have a near-constant ; a least square fit to [S/Fe] vs. [Fe/H] shows a slope of only . Among halo stars with the majority have , but two stars (previously shown to have low α/Fe ratios) have . For disk stars with , [S/Fe] decreases with increasing [Fe/H]. Hence, sulphur behaves like other typical α-capture elements, Mg, Si and Ca. Zinc, on the other hand, traces iron over three orders of magnitude in [Fe/H], although there is some evidence for a small systematic Zn overabundance () among metal-poor disk stars and for halo stars with . Recent measurements of S and Zn in ten damped Lyα systems (DLAs) with redshifts between 1.9 and 3.4 and zinc abundances in the range show an offset relative to the [S/Zn] – [Zn/H] relation in Galactic stars. Possible reasons for this offset are discussed, including low and intermittent star formation rates in DLAs.