Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...271..451f&link_type=abstract
Astronomy and Astrophysics, Vol. 271, p. 451 (1993)
Astronomy and Astrophysics
Astrophysics
123
Convection, Lines: Formation, Spectroscopy, Stars: Temperatures Of, Sun: Photosphere Of
Scientific paper
Based on horizontally homogeneous model atmospheres the analysis of the first members of the hydrogen Balmer line series leads to a revision of the convective efficiency near the surfaces of cool dwarf stars. The synthesis of the Balmer lines includes Stark and resonance broadening. It fits the observed profiles of Hα through Hδ in such different stars as the Sun, Procyon, and the extremely metal-poor subdwarfs G41-41 and HD 140283. It turns out that the existence of the two different but equally important line-broadening mechanisms requires a temperature stratification near continuum optical depth unity which cannot be reconciled with a mixing-length 1 ≃ 1... 2 Hp as is usually derived from stellar interior calculations. With such high values of 1 the synthesis of the Balmer lines leads to effective temperatures differing by as much as 400 K. Comparison of Hα and Hβ profiles instead results in a much smaller mixing-length, 1 = (0.5±0.3) Hp, which seems to fit for all FG-type dwarfs even in the metal-poor limit. Thus, for the first time, spectroscopic observations of stars lead directly to a consistent determination of the temperature stratification in the lower photosphere.
Axer Markus
Fuhrmann Klaus
Gehren Thomas
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