Line formation of neutral aluminium in the Sun.

Details Line formation of neutral aluminium in the Sun. Line formation of neutral aluminium in the Sun.

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...307..961b&link_type=abstract

Astronomy and Astrophysics, v.307, p.961-971

Astronomy and Astrophysics

Astrophysics

37

Atomic Processes, Line: Formation, Sun: Abundances, Sun: Photosphere, Stars: Abundances

Scientific paper

We investigate the formation of neutral aluminium lines in the solar photosphere using an atomic model containing 58 levels plus the ground state of Al II connected via radiative and collisional interaction. Synthetic line flux and intensity profiles are compared with the solar spectrum to study the relevant kinetic processes and their influence on level populations and line profiles. For neutral aluminium with its extremely large ground state photoionization cross-section near 2071 A the reduction of the ultraviolet radiation field due to metallic line absorption has to be taken into account using Kurucz' (1992) ODF opacities. In the photosphere of a cool star excitation and ionization due to collisions with neutral hydrogen can outweight electronic collisions. The influence of different types of collisional interactions with electrons and neutral hydrogen is therefore examined. As expected, the non-LTE effects in most of the solar Al I lines are small, irrespective of the details of the atomic model. The cores and innermost parts of the wings of the resonance lines at 3944 and 3961A are affected by only small deviations from the observed profiles, part of which is due to the uncertainty connected with the proper choice of the continuum flux in the region of the Ca II H+K lines. Since the first excited state, 4s^2^S , is slightly overpopulated with respect to both the 3p^2^P^o^ ground state and to 4p^2^P^o^ the strongest evidence for non-thermal excitation is found in the infrared lines at 1.3 and particularly at 12μm. Empirical evidence for the necessity to include neutral particle collisions in the kinetic equilibrium of aluminium arises from comparison of these lines with observations. General agreement with solar line profiles in the infrared and in the visible is found for an atomic model with both electronic collisions and a strongly reduced amount of neutral particle collisions. The solar model will serve as a reference for the investigation of cool metal-poor stars in which both the reduced electronic collision rates and the enhanced UV intensities lead us to expect more pronounced deviations from LTE.

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