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The Hubble Space Telescope Extragalactic Distance Scale Key Project. 1: The discovery of Cepheids and a new distance to M81
Freedman, Wendy L.; Hughes, Shaun M.; Madore, Barry F.; Mould, Jeremy R.; Lee, Myung Gyoon; Stetson, Peter; Kennicutt, Robert C.; Turner, Anne; Ferrarese, Laura; Ford, Holland; Graham, John A.; Hill, Robert; Hoessel, John G.; Huchra, John; Illingworth, Garth D.
AA(Carnegie Observatories, Pasadena, CA, US), AB(Carnegie Observatories, Pasadena, CA, US), AC(California Inst. of Technology, Pasadena, CA, US), AD(California Inst. of Technology, Pasadena, CA, US), AE(Carnegie Observatories, Pasadena, CA, US), AF(Carnegie Observatories, Pasadena, CA, US), AG(Steward Observatory, Tucson, AZ), AH(Steward Observatory, Tucson, AZ), AI(Steward Observatory, Tucson, AZ), AJ(Steward Observatory, Tucson, AZ), AK(Steward Observatory, Tucson, AZ), AL(Steward Observatory, Tucson, AZ), AM(Steward Observatory, Tucson, AZ), AN(Steward Observatory, Tucson, AZ), AO(Steward Observatory, Tucson, AZ)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 427, no. 2, p. 628-655 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Astrometry, Astronomical Photometry, Calibrating, Cepheid Variables, Distance, Scale (Ratio), Spiral Galaxies, Data Reduction, Data Sampling, Hubble Constant, Hubble Space Telescope, Interstellar Extinction, Red Shift, Stellar Luminosity, Stellar Magnitude
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We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu0 = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.

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Part  1     Part  2     Part  3     Part  5     Part  8     Part  6     Part  9     Part  4     Part 10     Part  7     Part 15     Part 11     Part 12     Part 13     Part 14     Part 18     Part 20     Part 16     Part 17     Part 21     Part 19     Part 24     Part 23     Part 22     Part 25     Part 26     Part 27     Part 28     Part 29     Part 30    

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