Searching for the Most Massive Stars in M31 and M33
Abstract
Our spiral neighbors M31 and M33 can be used as laboratories for testing our theories of massive star evolution. Since massive star evolution depends heavily metallicity, M31 and M33 play a particularly important role in this regard: M31 has a metallicity about 1.5x solar, while M33 possesses a metallicity gradient going from solar in the center to sub-solar in the outer regions. Complete samples of evolved massive stars have been identified in these galaxies, but little is known of their unevolved predecessors, the O-type stars. The upper-left portions of the H-R diagrams of M31 and M33 are virtually empty, not because of the scant numbers of massive stars, but from our lack of knowledge. We are proposing a series of UV SNAPs of the most active star-forming regions in M31 and M33. These regions were previously imaged as part of a Cycle 15 treasury proposal, and have good optical colors, but the UV images were severely affected by charge transfer efficiency issues when the data were taken near the end of WFPC2's life. Our goal is to use photometry from these images to help us identify the most massive stars in these galaxies.
- Publication:
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HST Proposal
- Pub Date:
- June 2016
- Bibcode:
- 2016hst..prop14707M