THE CONTRACTING MOLECULAR CORES el AND e2 IN W51

摘要

We report on observations of the star-forming region W51 in the NH_3 (J, K) = (1, 1) and (2, 2) transitions at 1.3 cm. These observations have much greater sensitivity than our previous observations and they allow a kinematic analysis of the motions of the gas in two small star-forming cores. We present evidence for radial contraction of the gas in W51 e2 onto a young star and possibly also for similar contraction near W51 e1. The H Ⅱ region/molecular core W51 e2 seems to be in a stage where the central star has already arrived on the main sequence, whereas the cooler gas on scales of 0.1-0.2 pc is still contracting onto the mass concentration at the center. In contrast to the interpretation of Rudolph et al., we propose that the contraction extends only over a few tenths of a parsec near e2 instead of over the entire W51 molecular cloud complex.