The nonsolar abundance ratios of Arcturus deduced from spectrum synthesis

Abstract

Using opacity distribution functions based on a newly expanded atomic and molecular line list, we have calculated a model atmosphere for Arcturus that reproduces the observed flux distribution. Individual line parameters in the list were adjusted to match the solar spectrum in a preliminary way, in the regions 5000-5500 Å, 6000-6500 Å, and 7500-9000 Å. The Arcturus model spectrum calculated with these adjustments reproduces well the profiles of all lines in the observed spectrum of the Griffin atlas for which the solar gf-values are well determined. The Arcturus model has an iron abundance [Fe/H] = -0.5 ± 0.1, a temperature T eff = 4300 ± 30 K, gravity log g = 1.5 ± 0.15, and an overabundance of the light metals. The factor of 2 enhancement in Arcturus of O, Mg, Si, Ca, and Ti is similar to that of halo stars of much lower metallicity and velocity about the Galactic center. This enhancement significantly affects the ionization equilibria and opacities of Arcturus.