Computer Science
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999alma.confe..72w&link_type=abstract
Science with the Atacama Large Millimeter Array (ALMA), Associated Universities, Inc., held October 6-8, 1999 at Carnegie Instit
Computer Science
Star Formation, W49N, Vla, Bima, Core, Hii
Scientific paper
We have made multi-frequency observations of the high mass star forming region W49N using the VLA and BIMA. The images, with resolution from 0.045 arcseconds (VLA at 7 mm) to 0.35 arcseconds (BIMA at 3.3 mm), obtain high dynamic range in an environment of complex emission, a hint of the capabilities to come with ALMA. Located on the far side of the Galaxy at a distance of 11.4 kpc, the W49N core contains more than a dozen ultracompact HII regions arranged in a 2 pc diameter ring (Dreher et al. 1984). This large scale organization has led to numerous speculations about mechanisms for triggering coherent events of high mass star formation. The large population of young sources appears at odds with the dynamical timescales for free expansion, a manifestation of the ``lifetime problem'' for ultracompact HII regions. The new millimeter images resolve individual ultracompact HII regions at the 500 AU size scale and reveal morphologies for many of them. Most show shell or ring structures. In all cases, the 3.3~mm emission is dominated by free-free emission; there is no evidence for any spectral breaks corresponding to the emergence of a dust component. Interestingly, the sources with rising radio spectral indices (S= is proportional to v-, alpha is greater than 0) also have the broadest H66 alpha radio recombination lines, phenomena likely explained by powerful ionized winds.
Depree Chris G.
Goss William Miller
McGrath Elizabeth
Welch William J.
Wilner David J.
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