Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...192..264g&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 192, no. 1-2, March 1988, p. 264-274.
Astronomy and Astrophysics
Astrophysics
58
Abundance, Barium, Early Stars, Magnesium, Stellar Spectra, Thermodynamic Equilibrium, A Stars, B Stars, Chemical Composition, Metal Ions, Stellar Atmospheres
Scientific paper
Based on high-dispersion photographic spectrograms in the visual spectral range, an abundance determination is carried out for magnesium and barium in the photosphere of Vega. Adopting an Atlas 6 model atmosphere with Teff = 9500 K and log g = 3.90, departures from LTE are investigated using model atoms with 71 + 28 (Mg I/Mg II) and 42 (Ba II) levels, respectively. Only small non-LTE abundance corrections (-0.03 dex) are found for Mg I and Mg II, while marked non-LTE effects are present for Ba II (+0.29 dex). A magnesium abundance of 7.00 + or - 0.15 and a barium abundance of 1.92 + or - 0.23 are deduced, implying a significant underabundance of magnesium, but only a mild deficiency of barium with respect to the sun. Satisfactory agreement exists between abundances inferred from both ionization stages of Mg. The Mg abundance obtained here agrees closely with other abundance determinations based on UV lines. The dependence of the derived abundances on various atomic and atmospheric parameters is discussed.
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