期刊
ASTROPHYSICAL JOURNAL
卷 541, 期 1, 页码 207-217出版社
UNIV CHICAGO PRESS
DOI: 10.1086/309416
关键词
Galaxy : abundances; radiative transfer; stars : abundances; stars : atmospheres
Abundances of alpha-elements such as Ca and Mg in disk and halo stars are usually derived from equivalent width lines measured on high-resolution spectra and assuming local thermodynamic equilibrium (LTE). In this paper, we present non-LTE differential abundances derived by computing the statistical equilibrium of Ca I and Mg I atoms, using high-resolution equivalent widths available in the literature for 252 dwarf to subgiant stars. These non-LTE abundances, combined with recent determination of non-LTE abundances of iron, seem to remove the dispersion of the [Ca/Fe] and [Mg/Fe] ratios in the galactic halo and disk phases, revealing new and surprising structures. These results have important consequences for chemical evolution models of the Galaxy. In addition, non-LTE abundance ratios for stars belonging to the M92 cluster apparently have the same behavior. More high-resolution observations, mainly of globular clusters, are urgently needed to confirm our results.
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