The Extragalactic Distance Scale Key Project. XVI. Cepheid Variables in an Inner Field of M101
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P.; Madore, Barry F.; Freedman, Wendy L.; Gibson, Brad K.; Stetson, Peter B.; Ferrarese, Laura; Saha, Abhijit; Graham, John A.; Mould, Jeremy R.; Ford, Holland C.; Hoessel, John G.; Hughes, Shaun M. G.; Sakai, Shoko; Harding, Paul; Rawson, Daya M.; Han, Mingsheng; Hill, Robert J.; Phelps, Randy L.; Silbermann, Nancy A.; Kennicutt, Robert C., Jr.; Turner, Anne
Canada, United States, Australia, United Kingdom
Abstract
We report on the identification of 255 candidate variable stars in a field located some 1.7 arcmin from the center of the late-type spiral galaxy M101 = NGC 5457, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. Photometric measurements in the F555W and F814W filters--analyzed independently with the DAOPHOT/ALLFRAME and DoPHOT software suites--have been transformed to the Johnson V and Kron-Cousins I standard magnitude systems. Periods and intensity-averaged mean magnitudes for 61 carefully selected candidate Cepheid variables with periods in the range 10-48 days indicate a reddening-corrected mean distance modulus (m - M)0 = 29.05 +/- 0.14 (if the true modulus of the Large Magellanic Cloud is 18.50 +/- 0.10, and if there is no dependence of the period-luminosity relation on metal abundance); results consistent with this are obtained whether or not the sample is expanded to include a larger fraction of the candidates. Applying a metallicity-dependent correction of +0.16 +/- 0.10 mag would increase this estimate to (m - M)0 = 29.21 +/- 0.17 mag.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by AURA, Inc., under NASA contract No. NAS 5-26555.