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

Zn abundances, derived from a model atmosphere analysis of the λ6362.35 Å $\ion{Zn}{i}$ line, are presented for 44 thin disk, 10 thick disk and 8 halo dwarf stars in the metallicity range $-1.0 < \mbox{\rm [Fe/H]}< +0.2$. It is found that [Zn/Fe] in thin disk stars shows a slight increasing trend with decreasing metallicity reaching a value $\mbox{\rm [Zn/Fe]}\simeq +0.1$ at $\mbox{\rm [Fe/H]}= -0.6$. The thick disk stars in the metallicity range $-0.9 < \mbox{\rm [Fe/H]}< -0.6$ have an average $\mbox{\rm [Zn/Fe]}\simeq +0.15$ dex, whereas five alpha-poor and Ni-poor halo stars in the same metallicity range have $\mbox{\rm [Zn/Fe]}\simeq 0.0$ 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