Title: Non-LTE analysis of neutral magnesium in cool stars ?
Abstract: Calculations of the statistical equilibrium of mag- nesium in the solar photosphere have shown that NLTE pop- ulations hardly affect Mg line formation in the Sun. However, in metal-poor dwarfs and giants the influence of electron col- lisions is reduced, and the ultraviolet radiation field, enhanced due to reduced background line opacity, results in more pro- nounced NLTE effects. In the photosphere of a cool star excita- tion and ionization due to collisions with neutral hydrogen can outweigh electron collisions. Analyses based on NLTE popu- lations lead to significantly higher Mg abundances than those calculated from LTE. We calculate magnesium abundances in 10 cool dwarfs and subgiants with metallicities from 2:29 to 0:0. The results are based on spectra of high-resolution and high signal-to-noise ratio. Stellar effective temperatures are de- rived from Balmer line profiles, surface gravities from Hippar- cos parallaxes and the wings of the Mgib triplet, and metal abundances and microturbulence velocities are obtained from LTE analyses of Feii line profiles. For stars with metallici- ties between 2:0 < (Fe/H) < 1:0 abundance corrections (Mg=H)NLTE LTE 0:05-0:11 are found. As expected the corrections increase with decreasing metal abundance, and they increase slightly with decreasing surface gravity. We also cal- culate the statistical equilibrium of magnesium for series of model atmospheres with different stellar parameters and find that (Mg=H)NLTE LTE increases with effective temperature between 5200 and 6500 K. For extremely metal-poor stars the abundance corrections approach (Mg=H)NLTE LTE 0:23 at (Fe/H) 3:0.
Publication Year: 2000
Publication Date: 2000-10-01
Language: en
Type: article
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Cited By Count: 2
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