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Proposal ID = 12465
Principle Investigator =  Paul A. Crowther  - University of Sheffield
Title = "A Massive Star Census of the Starburst Cluster R136"
Time = Apr 7, 2012, 06:31:53 - 12:23:57
Target =  R136
Instrument = STIS/CCD, STIS/FUV-MAMA

Background:

Until 2010, most astronomers believed the most massive stars in the universe were roughly 150 times the mass of the sun. There is now evidence, from the proposing team, that the limit could be higher, possibly as large as 300 times the mass of the sun. This is more than just an item for the Guinness Book of World Records, since it provides a test of our theoretical understanding of stars. The most massive stars should be near what is called the Eddington Limit, the mass at which the radiation pressure trying to blow the star apart equals the gravitational force trying to hold the star together. Most of the stars which appear to exceed this limit are in the young compact star cluster R136, in the Large Magellanic Clouds (LMC), a neighboring dwarf galaxy of our own Milky Way. The larger star forming region around R136 is known as 30 Doradus or the Tarantula Nebula. An important question concerning these new observations is whether the massive stars are actually multiple star systems (e.g., binary stars), with each of the component stars less than 150 solar masses. The proposed observations use the Space Telescope Imaging Spectrograph (STIS) at different epochs to determine whether the stars are single or double.

Paraphrasing from the abstract:

We propose to carry out a comprehensive census of the most massive stars in the central parsec (4") of the starburst cluster, R136, which powers the Tarantula Nebula in the LMC. R136 is both sufficiently massive that the upper mass function is richly populated and young enough that its most massive stars have yet to explode as supernovae. The identification of very massive stars in R136, up to 300 solar masses, raises general questions of star formation, binarity and feedback in young massive clusters. The proposed STIS spectral survey of ~36 stars more massive than ~50 solar masses within R136 is ground-breaking, of legacy value, and is specifically tailored to measure a number of properties including: a) stellar binarity; b) rotational velocities (relevant for predictions of rotational mixing); c) mass-loss properties; d) surface compositions; and f) radial velocities (relevant for runaway stars and cluster dynamics). This census will enable the mass function of very massive stars to be measured for the first time, as a result of incomplete and inadequate spectroscopy to date. It will also perfectly complement our Tarantula Survey, a ground-based VLT Large Programme, by including the most massive stars that are inaccessible to ground-based visual spectroscopy due to severe crowding. These surveys, together with existing integrated UV and optical studies will enable 30 Doradus to serve as a bona-fide template for unresolved extragalactic starburst regions.


You can find most of this information and more from the following webpage: http://www.stsci.edu/hst/ by entering "12465" in the Prop. ID box.