The [Zn/Fe] - [Fe/H] trend for disk and halo stars

Zn abundances, derived from a model atmosphere analysis of the λ6362.35 Å Zn I line, are presented for 44 thin disk, 10 thick disk and 8 halo dwarf stars in the metallicity range -1.0 < [Fe/H] < +0.2. It is found that [Zn/Fe] in thin disk stars shows a slight increasing trend with decreasing metallicity reaching a value [Zn/Fe] ≃ +0.1 at [Fe/H] = -0.6. The thick disk stars in the metallicity range -0.9 < [Fe/H] < -0.6 have an average [Zn/Fe] ≃ +0.15 dex, whereas five alpha-poor and Ni-poor halo stars in the same metallicity range have [Zn/Fe] ≃ 0.0 dex. These results indicate that Zn is not an exact tracer of Fe as often assumed in abundance studies of damped Lyman-alpha systems (DLAs). A better understanding of the nucleosynthesis of Zn is needed in order to obtain more detailed information on the past history of star formation in DLAs from e.g. the observed sulphur/zinc ratio.

Based on observations collected at the National Astronomical Observatories, Xinglong, China and the European Southern Observatory, La Silla, Chile (ESO No. 67.D-0106).