A new way to measure the departure from thermodynamic equilibrium in stellar atmospheres  

作　　者：Zhong-Quan Qu Long-Fei Hao Xiao-Li Yan Cheng-Lin Xu 

机构地区：[1]Yunnan Astronomical Observatory/National Astronomical Observatories, Chinese Academy of Sciences, Kunming 650011, China [2]Graduate School, Chinese Academy of Sciences, Beijing 100049, China [3]Mathematics Department, Yunnan Normal University, Kunming 650122, China

出　　处：《Chinese Journal of Astronomy and Astrophysics》2009年第2期205-212,共8页中国天文和天体物理学报（英文版）

基　　金：Supported by the National Natural Science Foundation of China;sponsored by the National Natural Science Foundation of China(No. 10673031); as well as the National Basic Research Program of China (973) under grant num-ber G2006CB806301.

摘　　要：A new way to measure the departure from thermodynamic equilibrium is proposed based on the departure factor which evaluates the deviation from a Boltzmann level distribution, used by Short and Hauschildt （2005） and others. The way is based on an explicit relationship describing the departure factor as a function of line to continuum source, dynamic temperature and line photon frequency, under three assumptions that the scattering can be neglected, the background continuum can be treated as a Planck function, and finally the complete redistribution can be true. It has the advantage that the departure can be very conveniently evaluated from the spectral analysis with only the radiative transfer involved. Some physical insights are recovered for some extreme cases. Some example calculations of the departure are presented for the quiet Sun, faint solar flare and strong solar flare for the generally used solar chromospheric lines： Hα, Hβ, CaII H, K and triplet. It is revealed that in the case of solar flares, the departure is less than thermodynamic equilibrium along the larger depth range than in the quiet sun due to chromospheric condensation. It becomes hard to distinguish the departures for the different lines of the same atom or ion. It is expected that this investigation can be constructive for studying stellar atmospheres in cases where the three assumptions are close to reality.A new way to measure the departure from thermodynamic equilibrium is proposed based on the departure factor which evaluates the deviation from a Boltzmann level distribution, used by Short and Hauschildt （2005） and others. The way is based on an explicit relationship describing the departure factor as a function of line to continuum source, dynamic temperature and line photon frequency, under three assumptions that the scattering can be neglected, the background continuum can be treated as a Planck function, and finally the complete redistribution can be true. It has the advantage that the departure can be very conveniently evaluated from the spectral analysis with only the radiative transfer involved. Some physical insights are recovered for some extreme cases. Some example calculations of the departure are presented for the quiet Sun, faint solar flare and strong solar flare for the generally used solar chromospheric lines： Hα, Hβ, CaII H, K and triplet. It is revealed that in the case of solar flares, the departure is less than thermodynamic equilibrium along the larger depth range than in the quiet sun due to chromospheric condensation. It becomes hard to distinguish the departures for the different lines of the same atom or ion. It is expected that this investigation can be constructive for studying stellar atmospheres in cases where the three assumptions are close to reality.

关 键 词：LINE formation -- radiative transfer -- stars ATMOSPHERES 

分 类 号：P144[天文地球—天体物理] O642.4[天文地球—天文学]