THE HUBBLE SPACE TELESCOPE KEY PROJECT ON THE EXTRAGALACTIC DISTANCE SCALE. XIX. THE DISCOVERY OF CEPHEIDS IN AND A NEW DISTANCE TO NGC 3198

摘要

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 WFPCZ of the Hubble Space Tele- scope (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 WFPCZ 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 estab- lishing the distance modulus. Period-luminosity relations were constructed in Johnson V and Kron- Cousins I by transforming the F555W and F814W to the standard system. We adopted a distance modulus of MU o = 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 MUo = 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 ± l.2 and ± 0.9 Mpc, respectively.