Revised Magnesium Abundances in Galactic Halo and Disk Stars

Abstract

A differential analysis of the magnesium abundances in 61 F-K dwarfs and subgiants with metallicities -2.6<[Fe/H]<+0.2 is performed based on published observational data. Fundamental parameters for 36 stars are determined: T eff from V-K and V-R; logg from HIPPARCOS parallaxes, and [Fe/H] and ξt from Fe II lines. The computations allow for non-LTE effects in the formation of the Mg I lines. For most of the stars, the standard errors in the Mg abundances do not exceed 0.07 dex. The metallicity dependence of [Mg/Fe] is analyzed. Magnesium shows a constant overabundance relative to Fe of 0.46±0.06 dex for metallicities -2.6<[Fe/H]<-0.7 Mg. The Mg overabundance decreases abruptly to ∼+0.27 dex at [Fe/H]⋍-0.7. At higher metallicities, the Mg abundance smoothly decreases to the solar value at [Fe/H]=0.0. Halo stars with metallicities [Fe/H]<-1.0 exhibit lower Mg overabundances ( ) compared to the [Mg/Fe] values for other stars with similar [Fe/H].