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On the boundaries of a convective zone and the extent of overshooting

Published online by Cambridge University Press:  01 April 2008

L. Deng  and
D. R. Xiong
L. Deng
Affiliation:
National Astronomical Observatories, Chinese Academy of Sciences, Beijing [email protected]
D. R. Xiong
Affiliation:
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing [email protected]
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Abstract

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In this work, we will show that a proper definition of the boundary of a convective zone should be the place where the convective energy flux (i.e. the correlation of turbulent velocity and temperature) changes its sign. Therefore, it is convectively unstable region when the flux is positive, and it is convective overshooting zone when the flux becomes negative. In our nonlocal convection theory, convection is already sub-adiabatic (∇ < ∇ad) far before reaching the unstable boundary; while in the overshooting zone below the convective zone, convection is sub-adiabatic and super-radiative (∇rad < ∇ < ∇ad). The transition between the adiabatic temperature gradient and the radiative one is continuous and smooth instead of a sudden switch. In the unstable zone, the temperature gradient is approaching radiative rather than going to adiabatic. The distance of convective overshooting is different for different physical quantities. The overshooting distance in the context of stellar evolution, measured by the extent of mixing of stellar matter, should be more extended than that of other physical quantities. It is estimated as large as 0.25–1.7 Hp depending on the evolutionary timescale.

Keywords

convectionstars:evolution
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S252: The Art of Modeling Stars in the 21st Century , April 2008 , pp. 83 - 88
Copyright
Copyright © International Astronomical Union 2008

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