[ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Photometry of Hodge 301: An “Old” Star Cluster in 30 Doradus

Abstract

We present Hubble Space Telescope Planetary Camera UVI data for Hodge301, the little-studied cluster 3' northwest of the central ionizingcluster R136 in 30 Doradus. The average reddening of Hodge 301 is foundto be {\lt}E_{B-V}{\gt}=0.28+/-0.05 mag from published infraredand ultraviolet photometry. Using two different sets of evolutionarymodels, we derive an age of about 20-25 Myr for Hodge 301, which makesit roughly 10 times as old as R136. Hodge 301 is the most prominentrepresentative of the oldest population in the 30 Dor starburst region,a region that has undergone multiple star formation events. This rangeof ages is an important consideration for the modeling of starburstregions. Hodge 301 shows a widened upper main sequence largely caused byBe stars. We present a list of Be star candidates. The slope of theinitial mass function for intermediate-mass, main-sequence stars rangingfrom 10 to 1.3 M_{solar} is found to be {$Γ$}=-1.4+/-0.1, ingood agreement with a Salpeter law. There is no indication for atruncation or change of slope of the initial mass function (IMF) withinthis mass range. In accordance with the age of Hodge 301, no obviouspre-main-sequence stars are seen down to about 1 M_{solar}. Weestimate that up to 41+/-7 stars with masses more than 12M_{solar} may have turned into supernovae since the formation ofthe cluster. Multiple supernova explosions are the most likely origin ofthe extremely violent gas motions and the diffuse X-ray emissionobserved in the cluster surroundings. Based on observations made withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc. under NASA contract NAS5-26555.