Bubbles, Shells, and Massive Stars in W49A: Observing the birth of a
massive star cluster
Nicole Homeier
The W49A star-forming region is embedded in a 10^6 M_sun molecular
cloud, one of the most massive in our Galaxy. It has been long known as
one of the most luminous giant radio H~II regions, containing 30-40
compact and ultracompact H~II regions and several recently discovered
hot cores. At NIR wavelengths, we have detected a previously unknown
massive star cluster embedded in the W49 molecular cloud. From our
analysis, the W49A cluster has a current inferred stellar mass of 2-7
10^4 M_sun, placing it in the mass regime of the extragalactic "super"
star clusters. In the combination of high mass and young age, W49A is
unique in the known Galaxy, and offers us a chance to observe clustered
massive star formation at some of the earliest stages, as well as the
impact of young massive stars on their parent molecular cloud. We find
that the massive stars appear to have formed in independent
"subclusters", although there is also evidence for triggered massive
star formation near the future cluster core. I will present and discuss
our JHK NTT observations of the densest region of the W49 molecular
cloud, as well as recent JHK adaptive optics observations from NACO on
the VLT of a ~80 M_sun star ionizing a compact H~II region.