Other
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9794m&link_type=abstract
HST Proposal ID #9794
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Hst Proposal Id #9794 Hot Stars
Scientific paper
Stellar winds are a ubiquitous phenomenon among high luminosity hot stars, and the resulting mass-loss has a significant effect on their evolution, as a very massive star might lose half its mass during its main-sequence life. There has been significant progress in understanding the physics of radiatively-driven winds, and simple theoretical parameterizations of mass-loss with stellar properties, such as luminosity, effective temperature, and surface gravity, have been developed. These provide good agreement with the observed mass-loss rates for Galactic stars. Scaling these mass-loss rates to other environments, where the metallicity Z is different than solar, requires a power-law in Z, but various studies have found values for this exponent ranging from 0.5 to 1.0. Here we are hampered by the scant range in metallicities covered by the observational database, which extends only from one-third solar {SMC} to solar {Milky Way}. We are proposing to extend this work to a sample of four O8-O8.5If stars in the Andromeda Galaxy {M31}, where the metallicity measured from HII regions is about twice solar. Significant ground-based and HST time has gone into setting the stage for this, but it is only in the last few years that good throughput in the FUV {thanks to STIS/MAMA} and large aperture optical telescopes have permitted the gathering of data of the quality needed for a quantitative spectroscopic analysis similar to what we can do for low-metallicity Magellanic Cloud stars. We have obtained most of the optical spectra we need with the newly reburbished 6.5-m MMT and are now requesting the FUV spectra that only HST/STIS can provide. The resulting analysis will not only yield mass-loss rates but also the physical parameters {Teff, log g, luminosity, radius, mass, and metallicity}, which can then be compared to their lower-metallicity counterparts. Parallel imaging with WFPC2 and ACS will provide data useful to ourselves and others for the study of the resolved stellar population of the Local Group galaxy most like our own.
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