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: Teff from V-K and V-R: log g from HIPPARCOS parallaxes, and [Fe/H] and ξl 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 ([Mg/Fe] = +0.22 dex) compared to the [Mg/Fe] values for other stars with similar [Fe/H]. © 2001 MAIK "Nauka/Interperiodica".