耀斑谱线轮廓不对称性研究

A Study on Spectral Line Asymmetry of Chr omospheric Flares

耀斑谱线轮廓的不对称性是耀斑动力学过程的一个重要观测事实。本文在一定的耀斑半经验大气模型基础上,计算了不同速度模式和色球凝聚下的Ha和CaⅡK谱线轮廓,从半经验角度探讨了大气各个层次的速度对Hα和CaⅡK谱线轮廓的影响。结果表明:耀斑早期短时间的Hα蓝不对称性可由位于过渡区的色球凝聚引起;随后的红不对称性是上部色球物质向下运动的结果;而后来出现的CaⅡK不对称性特征则可由色球中、下部具有10—20km/s的向下速度来解释。

Under a fixed model of chromospheric flare, we investigate the influences of Ha and CallK line profiles on various velocity distributions from a semiempirical view. The results show that: Ha line is very sensitive to the velocity in the upper chromosphere but insensitive to that in the middle or the lower part; the profile of CallK line has responses to velocity in any layer of the chromosphere, but the degree of CallK line asymmetry is weaker than that of Ha and it could be ignored if the velocity is as small as 10 km/s; the chromospheric condensa- tion in the lower part of the transition region has a strong influence on Ha line but contrary to CallK line; the typical characteristic of Ha line effected by the chromospheric condensation in the transition region is reversed blue asymmetry, i.e. the intensity of the blue peak is stronger than that of the red peak; the stronger the chromospheric condensation is, the more obvious the Ha line asymmetry appears; and so on. Summarizing the results calculated, we further obtained: The Hα blue asymmetry observed usually in the early stage of flares may be caused by the chromospheric condensation in the transition region; the Ha red asymmetry appeared later may result from the downward movemem of the upper chromosphere; and still later CallK asymmetry may be explained by the 10-20 km/s downward velocity in the middle or lower part of the chromosphere. This explanation is selfconsistent among the observations of Hα and CallK lines during the flares.