This paper presents the results of an extensive set of calculations about ionization equilibrium and NLTE effects on compact circumstellar HII regions embedded in clouds. In the mode! of a spherically symmetric and is...This paper presents the results of an extensive set of calculations about ionization equilibrium and NLTE effects on compact circumstellar HII regions embedded in clouds. In the mode! of a spherically symmetric and isothermal wind with a steady mass loss, pure hydrogen composition as well as Sobolev approximation, our research indicates that compact HII regions are far away from LTE state. The collisional ionization and photoionization from excited levels have great effects on the size of an HII region, the distribution of departure coefficients and the flux ratio of observed spectral lines. They can be used to explain the infrared line excess and the line deficit problems of YSOs. We conclude that it is unreasonable to infer the spectral type, mass loss rate and foreground extinction of the central star from optically thin line recombination theory.展开更多
基金Project supported by the National Natural Science Foundation of China and Astrophysical Branch of Chinese Astronomical Committee.
文摘This paper presents the results of an extensive set of calculations about ionization equilibrium and NLTE effects on compact circumstellar HII regions embedded in clouds. In the mode! of a spherically symmetric and isothermal wind with a steady mass loss, pure hydrogen composition as well as Sobolev approximation, our research indicates that compact HII regions are far away from LTE state. The collisional ionization and photoionization from excited levels have great effects on the size of an HII region, the distribution of departure coefficients and the flux ratio of observed spectral lines. They can be used to explain the infrared line excess and the line deficit problems of YSOs. We conclude that it is unreasonable to infer the spectral type, mass loss rate and foreground extinction of the central star from optically thin line recombination theory.
