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V. Charmandaris (Cornell University), M. Heydari-Malayeri (Obs. de Paris, France), M.R. Rosa (ST-ECF/ESO, Germany), H. Zinnecker (AIP, Germany), L. Deharveng (Obs. de Marseille, France)
We present our results of the first high resolution imaging using the Hubble Space Telescope (HST) of a sample of high excitation ``blobs'' (HEBs) which constitute a rare class of compact HII regions in the Magellanic Clouds. Contrary to the typical HII regions of these galaxies which are extended structures with sizes greater than 50pc, the compact HII regions are an order of magnitude smaller having diameters of less than about 4pc. HEBs are probably the final stages in the evolution of the ultra-compact HII regions -- whose Galactic counterparts are detected only at infrared and radio wavelengths.
The resolving power of HST enables us to identify the massive young stars enshrouded in those regions and present a census of their population. Contrary to what it was originally thought and despite their small size, the HEBs studied are not excited by a single massive star. Direct measurement of their spatially varying extinction reveals clumps of dust suggesting that the dust absorption is locally considerably higher than what was observed from integrated ground measurements. The peculiar morphology of the surrounding nebulae and the fine structure which appears in the images can be interpreted by the violent stellar winds of the exciting stars.
The subsolar metallicity of the SMC and LMC in conjunction with their location (being nearby and not affected by extinction due to the Galactic disk) makes the detailed study of their HEBs regions an excellent template for the understanding of star formation in low metallicity high-z galaxies.
Support for this work was provided by NASA through grant number GO-8247 from the STScI, which is operated by AURA, Inc., under NASA contract 26555.
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