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W. Brandner (JPL), E. K. Grebel (UWash), Y.-H. Chu (UIUC), S. Richling, H. W. Yorke (JPL), H. Dottori (UFRGS, Porto Alegre, Brazil), A. Moneti (ISO SOC, Vilspa, Spain), H. Zinnecker (AI Potsdam, Germany), S. D. Points (UIUC)
We report the discovery of three proplyd-like structures in the giant HII region NGC 3603. The emission nebulae are clearly resolved on new broad- and narrow-band HST/WFPC2 observations, and share the overall morphology of the proplyds in Orion. All three nebulae are rim-brightened and tear-drop shaped with the tails pointing away from the central ionizing cluster. This suggests that the starburst cluster in NGC 3603 with its more than 20 Wolf-Rayet and early O-type stars is the dominant source of ionization.
The brightest nebula, which has a projected separation of 1.3 pc from the cluster, has the spectral (excitation) characteristics of an Ultra Compact HII region. The optical spectra reveal the presence of an underlying, heavily reddened continuum source, which is also confirmed by near-infrared observations. The proplyd-like structures in NGC 3603 are about two orders of magnitude fainter than typical Ultra Compact HII regions, but with a typical extent of 6000 A.U. times 20000 A.U are also much larger in size than the proplyds in Orion.
The overall morphology and the spectral characteristics suggest that the proplyd-shaped structures in NGC 3603 might be the intermediate mass counterparts to the low-mass proplyds in Orion. We compare the observations with 2D radiation-hydrodynamics calculations of externally illuminated intermediate mass star-disk systems with the aim to determine mass-loss rates and evolutionary status of the NGC 3603 proplyds.
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