哈雷彗星主尾流的研究

哈雷彗星在日彗距较大时出现长而直的主彗尾（尾流），这是很有趣的。尾流一般是指等离子体尾流；但是，当地球接近彗星轨道面时，尘埃尾流可能叠加到主彗尾上。在一般感光波段宽的彗星底片上很难区分这两种尾流。本文选取哈雷彗星在不同日彗距的5条主尾流，作了光度测量和比较分析。得出沿各尾轴及其垂直方向几个截面的亮度分布、亮度半极大全宽、尾轴的视风差角和真风差角及彗尾长度。在所分析的蓝敏底片上，过近日点前的2个尾流肯定是等离子体尾流，而5个尾流的相似性以及其他证据说明它们主要都是等离子体尾流，尘埃彗尾的污染是次要的。

Five Main Tall Streamers of Comet Halley

It is of much interest that comet Halley showed very long and straight main tail (tail streamer) at larger heliocentric distance. The streamer refers usually to the plasma one. However, a dust streamer may superimpose to the main tail when the Earth is close to the cometary orbit plane, as well as the presence of neutral sodium in the tail ward direction of a few bright comets has been noted. Because of wide sensitive wave range of the photographic plate and projective effect, both the plasma streamer and the dust streamer in main tail of a cometary image may be superimposed and difficult to be distinguished from each other for lacking evidence. In this paper, photometry and geometric measurement of five main tail streamers of comet 1P/Halley at different heliocentric distances are made and compared. Brightness profiles along streamer axis and several transverse cuts, full widths at half maximum (FWHM) of the streamers, apparent and actual aberration (lag) angles of the axis as well as tail lengths are obtained. Among these streamers in blue light plates, two streamers before perihelion passage are definitely plasma ones. Similar photometric and geometric features of these five streamers as well as other evidence suggest that other three streamers are mainly plasma ones instead of dust ones and dust contamination (or sodium tail) may be secondary.