Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars
2012 (English)In: XXI INTERNATIONAL CONFERENCE ON SPECTRAL LINE SHAPES (ICSLS 2012), 2012, 012049- p.Conference paper (Refereed)
The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H <-> X(n'l') + H and charge transfer processes X(nl) + H <-> X+ + H- have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. . Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.
Place, publisher, year, edition, pages
2012. 012049- p.
, Journal of Physics Conference Series, ISSN 1742-6588 ; 397
IdentifiersURN: urn:nbn:se:uu:diva-193477DOI: 10.1088/1742-6596/397/1/012049ISI: 000312548700049OAI: oai:DiVA.org:uu-193477DiVA: diva2:602967
21st International Conference on Spectral Line Shapes (ICSLS), JUN 03-09, 2012, St Petersburg, RUSSIA