年轻星天体喷流的近红外成像观测进展

Recent Progress in the Near Infrared Imaging of Jets from Young Stellar Objects

分子氢的红外振动发射线是显现年轻星质量外流的重要谱线之一．自Ｇａｕｔｉｅｒ等人１９７６年在猎户座发现年轻星质量外流的分子氢发射开始，人们在银河系内几乎所有的恒星形成区都发现了这种线发射。研究表明，分子氢发射与年轻星周围的其它活动现象（如分子外流和光学喷流）之间有着非常密切的联系．红外和光学喷流代表了年轻星剧烈活动的两个侧面，是喷流与周围介质相互作用强弱不同的表现，这种作用还拖带周围介质，产生分子外流。光 学、红外喷流和分子外流组成了恒星形成区壮观的景象，它们是恒星形成活动的重要标志。 随着红外探测技术的飞速发展，对年轻星外流活动现象的观测越来越丰富和详细，使 人们对这种现象的本质越来越了解。在２０世纪９０年代ＮＩＣＭＯＳ等大阵列红外探测器投入 使用后，红外成像观测有了长足的进步．目前已在７０个左右的区域里发现了Ｈ２发射，这 一数字还在迅速增加。今后的研究主要可能向两个方向发展。其一是高分辨观测，进一步了 解Ｈ２发射的结构以及与光学喷流和分子外流之间的关系；其二是巡天观测，了解银河系内 的恒星形成区Ｈ２发射的大尺度结构和恒星形成的统计分布规律。

The infrared ro-vibrational lines of molecular hydrogen are the most important tracers of mass outflow around young stellar objects (YSOs). Since the first discovery by Gautier et al. in 1976, the molecular hydrogen lines have been detected in almost all star forming regions in the Galaxy over the subsequent decades. Further studies show that H2 line emissions are closely associated with other energetic activities around YSOs such as molecular outflows and optical jets. Infrared and optical jets are two different manifestations of the same jet interaction with ambient media. Such interaction leads to the entrainment of ambient material and subsequently drives molecular outflow. Optical/infrared jets and molecular outflows make up the spectacular scenery in the star forming regions and are the signposts of star forming activities. With the advent of the large array detector such as NICMOS in the 1990's, great progress has been made in near infrared imaging observation. So far about 70 regions have been detected in H2 emission, with the number increasing rapidly. Future development will be in two directions: observation at higher angular resolution should reveal the detailed structure of H2 jets, which will also help to understand the relation between H2 emissions, HH jet, and CO outflows; large scale survey will provide information on the large scale structure and distribution of H2 knots in star forming regions in the Galaxy.