On the boundaries of a convective zone and the extent of overshooting
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.
convection stars:evolution
L.Deng D.R.Xiong
National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012 Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210008
国际会议
The 252th Symposium of the International Astronomical Union(国际天文学联合会第252届研讨会)
海南三亚
英文
83-88
2008-04-06（万方平台首次上网日期，不代表论文的发表时间）