Extragalactic Distances: the Need for Accurate Photometry of Blue Supergiants and Cepheids

Details Extragalactic Distances: the Need for Accurate Photometry of Blue Supergiants and Cepheids Extragalactic Distances: the Need for Accurate Photometry of Blue Supergiants and Cepheids

Jul 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002hst..prop.9492b&link_type=abstract

HST Proposal ID #9492

Computer Science

Hst Proposal Id #9492

Scientific paper

The investigation of the Wind Momentum-Luminosity Relationship {WLR} of blue supergiant stars as an independent extragalactic distance indicator has reached a critical phase. Following our recent discovery and spectroscopic follow-up of several tens of stars outside of the Local Group in NGC 300 and NGC 3621, we can now calibrate the WLR in terms of spectral subtype and metallicity with a higher accuracy than hithertho possible with the statistically limited samples available in the nearby galaxies studied so far. This, however, requires high-resolution imaging to obtain accurate BVI photometry of a significant fraction of those stars for which we have spectroscopic information. This can be effectively accomplished with eight ACS/WFC fields in these two galaxies. As a further step, we can use the calibrated WLR to measure the first independent extragalactic distance. We then propose additional imaging of six ACS/WFC fields in M101 to select blue supergiant candidates for spectroscopic follow-up. Having recently discovered more than a hundred new Cepheids in NGC 300, the high-resolution imaging proposed for the photometry of blue supergiants can also be used, with no additional observing effort, to verify the effects of blending on the Cepheid distance to this galaxy, an important calibrator of secondary distance indicators.

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