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Paper: The Giant HII Region W49A: A Starbirth Cluster
Volume: 267, Hot Star Workshop III: the Earliest Stages of Massive Star Birth
Page: 297
Authors: Conti, P. S.; Blum, R. D.
Abstract: W49A is one of the most luminous giant HII regions in our Galaxy, containing numerous compact and ultracompact (UC) HII regions. The center holds a ``cluster'' of about 30 O stars, each within an individual UCHII region but completely obscured in optical wavelengths by local and intervening interstellar dust. Our recent deep K-band (2.2 micron) imaging toward the W49A cluster reveals two of the individual exciting stars, each associated with a point-like radio source, but the rest are invisible. The two K-band visible UCHII regions have radio properties which are not distinct from others which remain invisible in the near-IR. After a massive star is first born, the resultant surrounding ionized hydrogen region gradually expands and the dust opacity in the cocoon similarly lessens. These processes are related but not closely coupled. In the outer environs of W49A compact H II regions are visible in the near IR, along with candidate exciting stars. These are further along in emergence from their natal environment. The W49A region can serve as a template for the more luminous buried star clusters now being found in normal galaxies and starbursts.
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