HST Measurements of Cepheid Variables in an Inner Field of M101

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Session 6 -- Cepheid Variables and the Distance Scale
Display presentation, Monday, June 12, 1995, 9:20am - 6:30pm

[6.04] HST Measurements of Cepheid Variables in an Inner Field of M101

P.B. Stetson (DAO/HIA/NRC), A.~Saha (STScI), W.L.~Freedman, R.~Hill, R.~Phelps (OCIW), R.C.~Kennicutt, F.~Bresolin, P.~Harding, A.~Turner (Steward), J.R.~Mould (MSSSO), L.~Ferrarese, H.C.~Ford (JHU/STScI), J.A.~Graham (DTM/CIW), M.~Han, J.G.~Hoessel (Wisconsin), J.~Huchra (Harvard), S.M.G.~Hughes (RGO), G.D.~Illingworth, D.~Kelson (Lick), B.F.~Madore, N.~Silbermann, S.~Sakai (IPAC)

We present the results of recent observations of a field centered 1\Min7 from the core of the the nearby supergiant Sc-type spiral galaxy M101 (= NGC 5457). The data were obtained with the WFPC2 camera on the Hubble Space Telescope as part of the Key Project on the Extragalactic Distance Scale. This field will represent a crucial testbed for many of the algorithms and techniques that the Key Project will be applying to all its targets: we will present a direct comparison of results as obtained with independent photometric packages (DAOPHOT and DoPHOT), tests based on synthetic star images --- both ``constant stars'' and ``Cepheids'' ---, and experiments with the fully automatic detection of variables and fitting of light-curve parameters. Furthermore, comparison of results for the M101 inner field with those for a second field some 7\Min9 from the center will place new limits on the variation of the P-L relation with metallicity. Representative light curves for Cepheid variables detected within the field will be shown, as will calibrated color-magnitude diagrams for non-variable stars. These data will refine our knowledge of the distance to this galaxy and its fellow group members --- important calibrators of the Tully-Fisher and Type-II supernova expanding-photospheres distance indicators.

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