A Determination of the Chemical Composition of Alpha Centauri A from Strong Lines

Abstract

Using the theory of collisional line broadening developed by Anstee and O'Mara (1991, 1995) and the spectrum synthesis software developed by John Ross, the abundances of Fe, Mg, Ca and Na in Alpha Centauri A are determined from strong lines. The abundances are approximately 0.2 dex higher than in the Sun. The derived abundances are independent of non-thermal motions in the atmosphere of Alpha Centauri A. The microturbulence obtained from medium-strong lines using the abundances obtained from the strong lines is 1.34 +/- 0.12 km/s, i.e., 0.20 km/s larger than in the Sun, which is fully consistent with the lower surface gravity of Alpha Centauri A. This microturbulence can then be used in determination of the abundance of other elements for which there are no strong lines in the spectrum. This thesis is the first application of this theory to determine abundances and the microturbulence of Alpha Centauri A. Recent results are published by Doyle et al.(astro-ph/0407468)