Non-LTEmodelling of AL I lines in atmospheres of late-type stars

V. S. Menzhevitski ; V. V. Shimansky ; N. N. Shimanskaya

Učënye zapiski Kazanskogo universiteta. Seriâ Fiziko-matematičeskie nauki, Uchenye Zapiski Kazanskogo Universiteta. Seriya Fiziko-Matematicheskie Nauki, Tome 153 (2011) no. 2, pp. 95-101

Résumé

In this work, the results of the analysis of Al I lines forming in atmospheres of late-type stars (A–K) without assumption of local thermodynamic equilibrium are presented. We developed a 39-level model of aluminum atom containing levels with $l\leq3$ and $n\leq12$ of Al I, and a level corresponding to the ground state of Al II. Based on the study of the line profiles and equivalent widths in the solar spectrum, we refined some atomic parameters for Al I lines ($\lambda\lambda$ 3944.01 Å, 3961.52 Å, 6693.03 Å, 6698.68 Å, 7362.29 Å, 7836.13 Å). For the selected Al I lines, grids of non-LTE corrections to the Al abundance defined with the LTE assumption were calculated. The results of the calculations for Kurucz's atmosphere models (in a wide range of stellar parameters) allows us to conclude that the Al I atom is in an overionization state: the $3p$ level is underpopulated in the line formation region. This is due to the dominance of ionization processes from the ground level by UV radiation over the cascade transitions from the high-excited levels, which is caused by a great value of the $3p$ level ionization cross section. This effect becomes more pronounced with increasing temperature and decreasing metallicity of the star. Non-LTE corrections to the Al abundance reach $(0.15\div0.25)$ dex for subordinate line $\lambda$ 6698.68 Å, $(0.4\div0.7)$ dex for subordinate line $\lambda$ 7836.13 Å, $(0.2\div0.45)$ dex for resonance line $\lambda$ 3961.52 Å, and it is $(0.6\div0.8)$ dex in the case of low metallicity ($[\mathrm A]=-2.0$) for certain atmosphere models.

Détail

Keywords: chemical composition, aluminum abundance, statistical equilibrium, late-type stars
Mots-clés : line formation, non-LTE corrections.

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