The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XIX. The Discovery of Cepheids in and a New Distance to NGC 3198

Abstract

We report the detection of Cepheid variable stars and a new distance to the Sc spiral NGC 3198. NGC 3198 is one of 25 galaxies that have been observed with the WFPC2 of the Hubble Space Telescope (HST) for the purpose of measuring Cepheid distances. Eighteen of these galaxies were targeted by the HST Key Project on the Extragalactic Distance Scale, whose objective is to calibrate a variety of secondary distant indicators and determine the Hubble constant to an accuracy of 10%. NGC 3198 was selected as part of this sample because its type and orientation make it very suitable as a Tully-Fisher calibrator. The WFPC2 data are comprised of 13 epochs in F555W (∼V) and five epochs in F814W (∼I). Two different crowded-field photometry packages (DAOPHOT/ALLFRAME and DoPHOT) were used. The magnitudes derived from these two packages agree to within a few percent. We identified 78 Cepheid candidates in the period range from eight to > 50 days, of which 52 were selected for establishing the distance modulus. Period-luminosity relations were constructed in Johnson V and KronCousins I by transforming the F555W and F814W to the standard system. We adopted a distance modulus of μ0 = 18.50 ± 0.10 mag and mean reddening of E(B-V) = 0.10 mag to the Large Magellanic Cloud Cepheids and found a true distance modulus to NGC 3198 of μ0 = 30.80 ± 0.16 (random) ± 0.12 (systematic) mag. This modulus corresponds to a distance of 14.5 Mpc, with random and systematic errors of ± 1.2 and ± 0.9 Mpc, respectively.