Revised magnesium abundances in Galactic halo and disk stars

A differential analysis of the magnesium abundances in 61 F-K dwarfs anti s ubgiants with metallicities -2.6 < [Fe/H] < +0.2 is performed based on publ ished observational data. Fundamental parameters for 36 stars are determine d: T-eff from V-K and V-R; log g from HIPPARCOS parallaxes, and [Fe/H] and xi (l) 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 o f 0.46 +/- 0.06 dex for metallicities -2.6 < [Fe/H] < -0.7 ME. The Mg overa bundance decreases abruptly to similar to +0.27 dex at [Fe/H] similar or eq ual to -0.7. At higher metallicities, the Ms abundance smoothly decreases t o the solar value at [Fe/H] = 0.0. Halo stars with metallicities [Fe/H] < - 1.0 exhibit lower Mg overabundances ([<([Mg/Fe])over bar>] = +0.22 dex) com pared to the [Mg/Fe] values for other stars with similar [Fe/H]. (C) 2001 M AIK "Nauka/Interperiodica".