Welch W J, Dreher J W, Jackson J M, Terebey S, Vogel S N
Science. 1987 Dec 11;238(4833):1550-5. doi: 10.1126/science.238.4833.1550.
High-resolution molecular line and continuum radio images from the Hat Creek Radio Observatory and the Very Large Array suggest that the core of the W49A star-forming region is undergoing gravitational collapse. The radio continuum shows a 2-parsec ring of at least ten distinct ultracompact H-II regions, each associated with at least one O star. The ring is a region of large-scale, organized massive star formation. Recombination line velocities and HCO(+) excitation requirements indicate that the ring is rotating around 50,000 solar masses of material. Because the HCO(+) (1-0) line shows red-shifted absorption but blue-shifted emission, the molecular cloud core is believed to be collapsing toward the center of the ring. The HCO(+) radial velocities, as well as H-I, H(2)CO, and magnetic-field measurements, fit a simple model of inside-out gravitational collapse of a once magnetically supported cloud.
来自哈特溪射电天文台和甚大天线阵的高分辨率分子谱线和连续谱射电图像表明，W49A恒星形成区的核心正在经历引力坍缩。射电连续谱显示出一个直径2秒差距的环，其中至少有十个不同的超紧凑H-II区，每个H-II区至少与一颗O型星相关联。这个环是一个大规模、有组织的大质量恒星形成区域。复合谱线速度和HCO(+)激发条件表明，这个环正围绕着约50000个太阳质量的物质旋转。由于HCO(+)（1-0）谱线显示出红移吸收但蓝移发射，因此分子云核心被认为正在朝着环的中心坍缩。HCO(+)的径向速度以及H-I、H₂CO和磁场测量结果符合一个关于曾经由磁场支撑的云团由外向内引力坍缩的简单模型。
