The HST Key Project on the Extragalactic Distance Scale XXVI. The calibration of PopulationII secondary distance indicators and the value of the Hubble constant Astrophys

We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST). A total of 25 exposures (divided into 13 epochs) are obtained using the F555W filter (transformed to Johnson V), and nine exposures (divided into five epochs) using the F814W filter (transformed to Cousins I). Photometric reduction of the data is performed using two independent packages, DoPHOT and DAOPHOT II/ALLFRAME, which give very good agreement in the measured magnitudes. A total of 34 bona fide Cepheids, with periods ranging from 12 to over 60 days, are identified based on both sets of photometry. By fitting V and I period-luminosity relations, apparent distance moduli are derived assuming a Large Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc. under NASA Contract NO. NAS5-26555. Hubble Fellow California Institute of Technology, Pasadena CA 91125, USA Steward Observatories, University of Arizona, Tucson AZ 85721, USA European Southern Observatory, Garching, Germany Kitt Peak National Observatory, NOAO, Tucson AZ 85726, USA Dominion Astrophysical Observatory, Victoria, British Columbia V8X 4M6, Canada Carnegie Observatories, Pasadena CA 91101, USA Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, ANU, ACT 2611, Australia NASA/IPAC Extragalactic Database and California Institute of Technology, Pasadena CA 91125, USA Johns Hopkins University and Space Telescope Science Institute, Baltimore MD 21218, USA Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA University of Wisconsin, Madison WI 53706, USA Harvard Smithsonian Center for Astrophysics, Cambridge MA 02138 USA Royal Greenwich Observatory, Cambridge CB3 OHA, UK Lick Observatory, University of California, Santa Cruz CA 95064 USA