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Session 6 - HII Regions & Massive Star Formation.
Display session, Wednesday, January 07
Exhibit Hall,
R136 is the extremely populous star cluster at the heart of the 30 Doradus nebula. We have obtained HST/FOS spectra of 65 of the brightest blue stars to investigate the massive star population of this prototype ``super star cluster", probably what a very young globular cluster would resemble. We find that over half the stars in our sample are of spectral type O3, the hottest, most luminous and massive subclass. We have identified more O3 stars in this remarkable cluster than were previously known elsewhere. The age of R136 is very young, <1-2 Myr. Despite the preponderance of so many high mass stars, we find that the IMF is completely normal, with a Salpeter slope (\Gamma=-1.3\pm0.1) extending from 2.8 \cal M_ødot to >100 \cal M_ødot. The most massive stars are well above the highest mass tracks available (120 \cal M_ødot), and a conservative estimate places the highest mass star at \sim 150\cal M_ødot, making this the highest mass unevolved star yet found. Comparing this to other clusters suggests that we have yet to encounter any physical limit to how massive a star may form in nature, that the only limit we see is a statistical one, depending upon the richness (and age) of the cluster.
