The Chemical Composition of α Cen A: Strong Lines and the ABO Theory of Collisional Line Broadening

The mean abundances of Mg, Si, Ca, Ti, Cr, and Fe based on both strong and weak lines of α Cen A are determined by matching the observed line profiles with those synthesised from stellar atmospheric models and comparing these results with a similar analysis for the Sun. There is good agreement between the abundances from strong and weak lines. Strong lines should generally be an excellent indicator of abundance and far easier to measure than the weak lines normally used. Until the development of the Anstee, Barklem, and O'Mara (ABO) theory for collisional line broadening, the uncertainty in the value of the damping constant prevented strong lines being used for abundance determinations other than in close differential analyses. We found that α Cen A has a mean overabundance of 0.12 +/- 0.06 dex compared to solar mean abundances. This result agrees remarkably well with previous studies that did not use strong lines or the ABO theory for collisional line broadening. Our result supports the conclusion that reliable abundances can be derived from strong lines provided this new theory for line broadening is used to calculate the van der Waals damping.