| Authors | Silbermann, N. A.; Harding, Paul; Ferrarese, Laura; Stetson, Peter B.; Madore, Barry F.; Kennicutt, Robert C., Jr.; Freedman, Wendy L.; Mould, Jeremy R.; Bresolin, Fabio; Ford, Holland; Gibson, Brad K.; Graham, John A.; Han, Mingsheng; Hoessel, John G.; Hill, Robert J.; Huchra, John; Hughes, Shaun M. G.; Illingworth, Garth D.; Kelson, Dan; Macri, Lucas; Phelps, Randy; Rawson, Daya; Sakai, Shoko; Turner, Anne |
| Abstract | We report the detection of Cepheid variable stars in the barred spiral galaxy NGC 1365, located in the Fornax cluster, using the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2). Twelve V (F555W) and four I (F814W) epochs of observation were obtained. The two photometry packages ALLFRAME and DoPHOT were separately used to obtain profile-fitting photometry of all the stars in the HST field. The search for Cepheid variable stars resulted in a sample of 52 variables, with periods between 14 and 60 days, common to both data sets. ALLFRAME photometry and light curves of the Cepheids are presented. A subset of 34 Cepheids were selected on the basis of period, light curve shape, similar ALLFRAME and DoPHOT periods, color, and relative crowding, to fit the Cepheid period-luminosity relations in V and I for both ALLFRAME and DoPHOT. The measured distance modulus to NGC 1365 from the ALLFRAME photometry is 31.31+/-0.20 (random)+/-0.18 (systematic) mag, corresponding to a distance of 18.3+/-1.7 (random)+/-1.6 (systematic) Mpc. The reddening is measured to be E(V-I)=0.16+/-0.08 mag. These values are in excellent agreement with those obtained using the DoPHOT photometry, namely a distance modulus of 31.26+/-0.10 mag and a reddening of 0.15+/-0.10 mag (internal errors only). 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 NAS5-26555. |
