Abundances in field dwarf stars. III - Magnesium abundances

A spectrum synthesis technique is applied to derive intermediate dispersions spectra of 108 field dwarf stars and three Hyades dwarfs in order to calculate the Mg abundances relative to Fe. The synthetic spectra were calculated using dwarf model atmospheres in the MOOG program with inputs of atomic and molecular line data from previous surveys. A complete listing of the molecular Mg abundances calculated is provided. As noted by other researchers, Mg is overabundant in halo stars in comparison with Fe abundances, indicating that the excess Mg was produced by stellar nucleosynthesis. The overabundance was present whenever the forbidden Fe/forbidden H ratio was less than -1. The mean value of the forbidden Mg/forbidden Fe ratio in these stars was +0.24. The process which produced the Mg overabundance may be responsible for an observed oxygen overabundance in the same halo stars.