WLR Distances from Accurate Multi-Color WFPC2 Photometry of A & B Supergiants in M31 and M33

Details WLR Distances from Accurate Multi-Color WFPC2 Photometry of A & B Supergiants in M31 and M33 WLR Distances from Accurate Multi-Color WFPC2 Photometry of A & B Supergiants in M31 and M33

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6651m&link_type=abstract

HST Proposal ID #6651

Computer Science

Hst Proposal Id #6651 Hot Stars

Scientific paper

We propose to acquire WFPC2 multi-color photometry of A and B supergiant stars in M31 and M33 with a precision far exceeding that of existing ground-based estimates. The resulting WFPC2 magnitudes and colors will be used to determine distances to the hot stars using the Wind-momentum Luminosity Relationship {WLR}, in conjunction with existing moderate- and high- resolution spectra from 4-m class telescopes and the 10-m Keck-I telescope, respectively. The radiation-driven stellar wind momenta and metallicities derived from our high S/N spectra translate via the WLR into the intrinsic stellar luminosities; HST photometry is now crucial for distance determination. First, accurate distance moduli require accurate apparent magnitudes, which in the crowded fields of the M31 and M33 spiral arms demand the high spatial resolution of HST. Second, our model atmosphere analyses of the stellar spectra permit us to determine the extinction to each object by comparing the expected and observed {reddened} colors, where again the accuracy afforded by HST is critical. Third, implicit to the WLR method is the assumption that the objects are single highly luminous stars as opposed to tight associations {unresolved from the ground}, an assumption we seek to test with WFPC2 imagery. The resulting WLR distances to M31 and M33 will be compared to the distances from Cepheids {where metallicity and extinction influences are less tractable}, as a basis for extending the WLR method to larger distances.

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