Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...138..246d&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 138, no. 2, Sept. 1984, p. 246-252.
Astronomy and Astrophysics
Astrophysics
67
Atmospheric Turbulence, Flow Stability, Photosphere, Stellar Atmospheres, Supergiant Stars, Eddington Approximation, Hertzsprung-Russell Diagram, Shock Wave Propagation, Stellar Mass Ejection
Scientific paper
The author examines the consequences of the hypothesis that the stability limit of the atmospheres of hypergiants is reached when the effective acceleration of gravity geff = ggrav(1 - Γ)-gturb ≈ 0, where ggrav = GM/R2, gturb is the outward acceleration due to the gradient of turbulent pressure, and Γ is the Eddington ratio |grad/ggrav|. In stars close to the stability limit dissipation of mechanical energy builds up a field of supersonic turbulent motions in the photosphere which tends to destabilize the atmosphere. The larger the absolute luminosity, the deeper in the photosphere dissipation becomes important. This manifests itself in a rate of mass-loss, increasing with L. For near-unstable stars with Te ≈ 104K the rate of mass-loss is predicted to be nearly by a factor ten larger for a star brighter by one magnitude. This effect greatly changes the evolutionary tracks and explains why brighter stars have not been detected.
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