How to define the boundaries of a convective zone, and how extended is overshooting ?

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	How to define the boundaries of a convective zone, and how extended is overshooting ?
	Deng, L.1; Xiong, D. R.2
刊名	MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
	2008-06-01
卷号	386 期号:4 页码:1979-1989
关键词	convection stars : evolution
ISSN号	0035-8711
英文摘要	In non-local convection theory, convection extends without limit and therefore an apparent boundary cannot be defined clearly, as in local theory. From the requirement that a similar structure for both local and non-local models has the same depth of convection zone, and taking into account the driving mechanism of turbulent convection, we argue 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 a convectively unstable region when the flux is positive, and it is a convective overshooting zone when the flux becomes negative. The physical picture of the overshooting zone drawn by the usual non-local mixing-length theory is incorrect. In fact, convection is already subadiabatic (del < del(ad)) long before reaching the unstable boundary, while in the overshooting zone below the convective zone, convection is subadiabatic and superradiative (del(rad) < del < del(ad)). The transition between the adiabatic and radiative temperature gradients is continuous and smooth instead of being a sudden switch. In the unstable zone, the temperature gradient approaches a radiative temperature gradient rather than an adiabatic temperature gradient. We would like to note again that the overshooting distance is different for different physical quantities. In an overshooting zone at deep stellar interiors, the e-folding lengths of turbulent velocity and temperature are about 0.3H(P), whereas that of the velocity-temperature correlation is much shorter, about 0.09H(P). The overshooting distance in the context of stellar evolution, measured by the extent of the mixing of stellar matter, should be more extended. It is estimated to be as large as 0.25-1.7H(P) depending on the evolutionary time-scale. The larger the overshooting distance, the longer the time-scales. This is because of the participation of the extended overshooting tail in the mixing process.
学科主题	Astronomy & Astrophysics
WOS标题词	Science & Technology ; Physical Sciences
类目[WOS]	Astronomy & Astrophysics
研究领域[WOS]	Astronomy & Astrophysics
关键词[WOS]	MIXING-LENGTH CONVECTION ; TURBULENT CONVECTION ; NONLOCAL CONVECTION ; PULSATIONAL STABILITY ; SOLAR PHOTOSPHERE ; VARIABLE-STARS ; MASSIVE STARS ; STELLAR ATMOSPHERES ; HEIGHT DEPENDENCE ; MAIN-SEQUENCE
收录类别	SCI
语种	英语
WOS记录号	WOS:000255944100018
公开日期	2015-04-20
内容类型	期刊论文
源URL	[http://libir.pmo.ac.cn/handle/332002/11208]
专题	紫金山天文台_院士文集_熊大闰
作者单位	1.Chinese Acad Sci, Natl Astron Observ, Beijing 100012, Peoples R China 2.Chinese Acad Sci, Purple Mt Observ, Nanjing 210008, Peoples R China
推荐引用方式 GB/T 7714	Deng, L.,Xiong, D. R.. How to define the boundaries of a convective zone, and how extended is overshooting ?[J]. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,2008,386(4):1979-1989.
APA	Deng, L.,&Xiong, D. R..(2008).How to define the boundaries of a convective zone, and how extended is overshooting ?.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY,386(4),1979-1989.
MLA	Deng, L.,et al."How to define the boundaries of a convective zone, and how extended is overshooting ?".MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 386.4(2008):1979-1989.