Hot cores in W49N and the timescale for hot core evolution

We present subarcsecond resolution observations of the star-forming region W49N made with the Berkeley-Illinois-Maryland Association array at 1.4 mm w avelength in the continuum and CH3CN lines. The J = 12-11 continuum image, at a resolution of 0".18 (2000 AU), shows many of the previously identified ultracompact H II regions and at least one new source whose steep spectrum to short wavelengths indicates dust emission. This compact dust concentrat ion also shows the strongest CH3CN emission in the region. Additional peaks of CH3CN emission likely mark hot cores produced by other deeply embedded young massive stars that may be precursors to O-type stars like those that power the ultracompact H II regions. The number ratio of hot cores to ultra compact H II regions found in W49N provides a measure of the relative times cales of these early evolutionary phases. Although the samples are small, t he source counts suggest that the hot core lifetime is most likely shorter than, but comparable to, the ultracompact H II region lifetime.