Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997azh....74..601b&link_type=abstract
Astronomicheskij Zhurnal, vol. 74, p. 601
Astronomy and Astrophysics
Astronomy
1
F Stars, G Stars, Stellar Atmospheres, Strontium, Metal Ions, Atmospheric Composition, Statistical Analysis, Radiative Transfer, Ground State, Electron Transitions, Resonance Lines, Thermodynamic Equilibrium
Scientific paper
The statistical equilibrium of Sr II in the atmospheres of stars with T(eff) = 5500-6500 K, log g = 1.0-4.5, and M/H from 0 to -3 has been analyzed for the first time. For Sr II, the pumping of excited states by chains of radiative bound-bound (b-b) transitions starting from the ground level and the subsequent photoionization from these states underlie the mechanism of departures from LTE. As a result, the upper excited levels and the Sr III continuum are overpopulated relative to the equilibrium state, the population of the ground 5s level is essentially constant, and the 5p level is depopulated when the b-b transitions are strong (in stars with M/H = 0 and -1) and is overpopulated when the b-b transitions from it are unable to remove the pumping produced by the resonance 5s-5p transition (stars with M/H = -2 and -3). As a consequence, the subordinate lines that arise during the transitions from the 5p level weaken compared to the LTE case over the entire range of the parameters, while the resonance lines strengthen for M/H = 0 and -1 and weakened for M/H = -2 and -3. In stars with normal heavy-element abundances, the departures from LTE for all Sr II lines, except for the infrared triplet in the 4d-5p transition (10400 A) are small: the non-LTE corrections to the strontium abundance do not exceed 0.05 dex.
Belyakova E. V.
Mashonkina Lyudmila I.
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