Sulphur and zinc abundances in Galactic stars and damped Lyα systems

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 λλ8694.0, 8694.6 and λλ9212.9, 9237.5 SI lines. In addition, iron abundances have been determined from 19 Fell lines and zinc abundances from the λλ4722.2,4810.5 lines. The abundances are based on a classical ID, 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 -3.2 -1, [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 ([Zn/Fe] ≃ +0.1) among metal-poor disk stars and for halo stars with [Fe/H] < -2.0. 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 -2.1 < [Zn/H] < -0.15 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.