The HST Key Project on the Extragalactic Distance Scale XII. The Discovery of Cepheids and a New Distance to NGC 2541

摘要

We report the detection of Cepheids and a new distance to the spiral galaxyNGC 2541, based on data obtained with the Wide Field and Planetary Camera 2 onboard the Hubble Space Telescope (HST). A total of 25 exposures (divided into13 epochs) are obtained using the F555W filter (transformed to Johnson V), andnine exposures (divided into five epochs) using the F814W filter (transformedto Cousins I). Photometric reduction of the data is performed using twoindependent packages, DoPHOT and DAOPHOT II/ALLFRAME, which give very goodagreement in the measured magnitudes. A total of 34 bona fide Cepheids, withperiods ranging from 12 to over 60 days, are identified based on both sets ofphotometry. By fitting V and I period-luminosity relations, apparent distancemoduli are derived assuming a Large Magellanic Cloud distance modulus and meancolor excess of 18.50 +/- 0.10 mag and E(B-V) = 0.10 mag respectively. AdoptingA(V)/E(V-I)=2.45, we obtain a true distance modulus to NGC 2541 of 30.47 +/-0.11 (random) +/- 0.12 (systematic) mag (D = 12.4 +/- 0.6 (random) +/- 0.7(systematic) Mpc), and a total (Galactic plus internal) mean color excessE(B-V) = 0.08 +/- 0.05 (internal error) mag.