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Astron. Astrophys. 317, 114-120 (1997)

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The effect of turbulent pressure on the red giants and AGB stars

I. On the internal structure and evolution

S.Y. Jiang and R.Q. Huang

Yunnan observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, P.R. China

Received 24 January 1996 / Accepted 7 May 1996

Abstract

The expressions for the turbulent pressure, equation of state and thermodynamic quantities taking account of turbulent pressure are derived in the framework of the mixing-length theory of convection. The numerical computations indicate that the turbulent pressure in the region close to the surface of a red giant or an AGB star can reach a value of 30-40 percent of the total pressure. A comparison of the evolution of a star with [FORMULA] from the zero-age main sequence to the AGB stage adopting turbulent pressure with that of the neglected turbulent pressure shows that the effect of turbulent pressure on the internal structure and evolution in the phase from the He-core burning stage to the AGB stage is significant. A similar investigation for the star of [FORMULA] shows that the effect of turbulent pressure on the internal structure in the same evolutionary phase is small. However, the effect of turbulent pressure on the evolutional track in the AGB phase is obvious.

Key words: stars: AGB — stars: interiors — stars:evolution — convection — turbulence

Send offprint requests to: R.Q. Huang

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© European Southern Observatory (ESO) 1997

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