Evidence for departures from LTE in Na and Al in late-type giants

Abstract
Ten G7–K4 giants were analysed to determine the abundances of the elements Na, Mg, Al, Si, Ti and Fe. It was found that the abundances of Mg, Si and Ti agreed with the results of analyses of dwarfs by Tomkin, Lambert & Balachandran and Edvardsson, Gustafsson & Nissen, but the abundances of Na and Al were found to be enhanced with respect to the dwarfs by approximately 0.3 dex. It is contended that the Na and Al lines are affected by departures from LTE and that the LTE analyses of Na and Al in giants and supergiants are thus in error. Also it is shown that if the Na and Al abundances in the giants are corrected to agree with the dwarfs then the observational data agrees much better with theoretical studies of explosive nucleosynthesis such as that of Pardo, Couch & Arnett.

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