A homogeneous set of ground-based BVRI observations of similar to600 Cepheids is presented to check the Cepheid period-luminosity zero point for the Large Magellanic Cloud (LMC). The sample of Cepheids is completely self-contained and has been reduced consistently to eliminate photometric differences caused by combining multiple sources of photometry.The Cepheid distances to nearby galaxies obtained by the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale were computed assuming a "standard" PL relation based on a compilation of photoelectric observations of 34 Cepheids and a standard distance modulus to the LMC of 18.50. The final Key Project results substituted a statistically stronger PL relation obtained by the OGLE collaboration. In this paper we compare our data with the OGLE PL relation; the subsample of LMC Cepheids with similar periods to those discovered in the nearby galaxies is fainter at the relevant periods by 0.04 +/- 0.02 mag than the OGLE sample. Substituting in turn this PL relation for that of the OGLE collaboration would raise the Hubble constant by 2% +/- 1%, a correction which is not significant.The multicolor data set will also be useful in considering the effects of reddening and chemical composition and deriving an improved Cepheid period-luminosity relation for the LMC.

The distance to NGC 1425 has been derived from Cepheid variables, as part of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. Thirteen F555W (V) and eight F814W (I) epochs of cosmic-ray-split Wide Field Planetary Camera 2 observations were obtained. Twenty-nine Cepheids were discovered, with periods ranging from 16 to 63 days. Adopting a Large Magellanic Cloud distance modulus and extinction of 18.50 ± 0.10 mag and E(V-I) = 0.13 mag, respectively, a true reddening-corrected distance modulus (based on an analysis employing the ALLFRAME software package) of 31.73 ± 0.16 (random) ± 0.17 (systematic) mag was determined for NGC 1425. The corresponding distance of 22.2 ± 1.0 (random) ± 1.0 (systematic) Mpc is in satisfactory agreement with that found with an independent analysis based on the DoPHOT photometry package.

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 Wide Field and Planetary Camera 2. 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, in common with both datasets. 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).

We report the discovery of Cepheid variable stars in the galaxy NGC 4414, as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale. Observations were obtained with the HST Wide-Field and Planetary Camera 2 (WFPC2) for 13 epochs at V (F555W) and 4 at I (F814W). Photometry was performed using two independent programs, DoPHOT and DAOPHOT/ALLFRAME. We find 11 Cepheids with high-quality light curves and well-determined periods of 19-70 days. Nine of these Cepheids are used in fitting the period-luminosity relation. Assuming an LMC distance modulus of 18.50 mag and E(B-V) = 0.10 mag, we derive a reddening-corrected distance modulus for NGC 4414 of 31.41 +/- 0.17 (random) +/- 0.16 (systematic) mag, corresponding to a distance of 19.1 +/- 1.5 (random) +/- 1.4 (systematic) Mpc. We derive a mean color excess for NGC 4414 of E(V-I) = 0.02 +/- 0.05 mag. NGC 4414 is a calibrator of the Tully-Fisher and Type Ia supernova secondary distance indicators, and we briefly discuss the implications of the new distance for these methods.

The age of NGC 1651 is 1.6 ± 0.4 billion yr. This letter shows that accurate age determinations of young LMC clusters are achievable with aperture photometry of Wide Field Planetary Camera 2 (WFPC2) images taken in a single orbit of the HST.

Uncertainty in the metal abundance dependence of the Cepheid variable period- luminosity (PL) relation remains one of the outstanding sources of systematic error in the extragalactic distance scale and Hubble constant. To test for such a metallicity dependence, we have used the WFPC2 camera on the Hubble Space Telescope (HST) to observe Cepheids in two fields in the nearby spiral galaxy M101, which span a range in oxygen abundance of 0.7+-0.15 dex. A differential analysis of the PL relations in V and I in the two fields yields a marginally significant change in the inferred distance modulus on metal abundance, with d(m-M)/d[O/H] = -0.24+-0.16 mag/dex. The trend is in the theoretically predicted sense that metal-rich Cepheids appear brighter and closer than metal-poor stars. External comparisons of Cepheid distances with those derived from three other distance indicators, in particular the tip of the red giant branch method, further constrain the magnitude of any Z-dependence of the PL relation at V and I. The overall effects of any metallicity dependence on the distance scale derived with HST will be of the order of a few percent or less for most applications, though distances to individual galaxies at the extremes of the metal abundance range may be affected at the 10