Bibcode
McCarthy, J. K.; Kudritzki, R.-P.; Lennon, D.; Venn, K. A.; Smartt, S. J.; Herrero, A.
Referencia bibliográfica
American Astronomical Society, 198th AAS Meeting, #95.04; Bulletin of the American Astronomical Society, Vol. 33, p.1182
Fecha de publicación:
11
2001
Número de citas
0
Número de citas referidas
0
Descripción
We report the first results of a Hubble Space Telescope (HST) program
which performed WFPC2 multi-color imaging of a sample of A- and B-type
supergiant stars in M31 and M33. This sample has previously been studied
by us spectroscopically with the High Resolution Echelle Spectrograph
(HIRES) on the 10m Keck-I Telescope. In particular, fits to the
P-Cygni-like stellar Hα line profiles using state-of-the-art
non-LTE unified model atmospheres have provided us with measures of the
momentum in the stellar wind of each supergiant. When combined with
metallicity information from our analyses of the HIRES absorption line
spectra, these radiation-driven wind momenta allow us to determine the
intrinsic stellar luminosities (and hence distances) via the
Wind-momentum Luminosity Relation (WLR). The HST photometry reported
here is a critical ingredient for this work, as it permits us to improve
upon earlier ground-based apparent magnitudes for these objects (located
in the crowded fields of M31 and M33 spiral arm OB Associations) and
consequently to derive more precise distance moduli. Furthermore, the
accurate photometric colors reported here will improve our determination
of extinction to each object individually, via comparision with the
intrinsic colors of the best-fit model atmospheres. Lastly, an implicit
assumption of the WLR method is that the objects are highly-luminous
single stars (not tight multiple star groupings unresolved from the
ground), an assumption the HST imagery has allowed us to test. Support
of this work from the Space Telescope Science Institute in grant GO-6651
is gratefully acknowledged.