Star Formation in W49A: Gravitational Collapse of the Molecular Cloud Core Toward a Ring of Massive Stars
WM. J. WELCH 1,
J. W. DREHER 1,
J. M. JACKSON 1,
S. TEREBEY 1, and
S. N. VOGEL 1
1 Director, Radio Astronomy Laboratory, University of California, Berkeley, CA 94720.
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, H2CO, and magnetic-field measurements, fit a simple model of inside-out gravitational collapse of a once magnetically supported cloud.
Submitted on May 27, 1987
Accepted on October 28, 1987
