Measuring of short-duration meteor trains: altitude distribution of luminescence by double-station meteor observation with image intensified video cameras

流星出現直後にはごく稀に流星経路をなぞるように細い発光体が見える。それは短時間で減光し、形を変えながら消失する。これを流星痕と呼ぶ。流星痕の発生確率が最も高いのは毎年11月中旬に出現する「しし座流星群」である。我々はしし座流星群の2001年大出現で、イメージインテンシファイアを使用した流星の2点観測を実施した。動体検出ソフトウェアの使用により、動画から発光継続時間が短い流星痕（以下、短痕）を効率よく抽出できた。本研究では、しし座流星群に属する流星起源の短痕18例、しし群以外の流星起源の短痕8例、計26例の短痕を測定して発光高度と継続時間を求めた。その結果、（1）短痕は平均的に120kmから96kmの範囲で発光する。（2）短痕発生後、上端側は時間経過とともにその高度を直線的に徐々に低下させる一方で、下端側は母流星突入に伴い低高度側へ一気に成長し短痕長の最大を迎えた後、対数関数の漸近曲線的に上昇し、短痕消失直前には平均高度107kmに収れんする。（3）短痕の継続時間は短いもので0.1秒、最長で5秒。（4）母流星絶対等級と短痕の継続時間に有意な相関がある。（5）短痕の継続時間はOI557.7nm（励起状態特性寿命0.7秒）発光を仮定すれば説明できる可能性が高い、ことが分かった。Just after appearing of meteors, faint illuminating trails can rarely be seen along their trajectories. The luminescence, so-called meteor trains, rapidly disappear with changing their shapes in the sky. Meteor shower with the most frequent appearance rate of meteor trains is “Leonid.” In 2001, during an encounter of Leonid meteor storm in Japan, double-station observation of meteors was carried out by using image-intensified (I.I.) video cameras. Purpose of the I.I. video observation was to obtain precise trajectory parameters of Leonid meteors, however, many video clips of meteors with meteor trains of short duration within 3 s (short-duration meteor trains, hereafter) were found. By using a motion-detection software, 26 short-duration meteor trains (18 examples of Leonids as well as 8 of sporadic meteors) were successfully picked out, deriving altitude distribution of short-duration meteor trains. As a result, (1) short-duration meteor trains averagely appeared between 120 km and 96 km altitude, (2) altitude distribution of short-duration meteor trains averagely changes in time to be finally centered at around 107 km, with having linear dependence for their upper limit altitudes as well as logarithmic dependence for lower limits, (3) duration time of short-duration meteor trains was in a range between 0.1 s to 5 s, (4) high correlation between absolute magnitudes of parent meteors and duration time of short-duration meteor trains, and (5) the altitude distribution of short-duration meteor trains could be explained with OI 557.7nm luminescence and collision (quenching) process with surrounding upper atmosphere.査読あり論