| Authors | Rawson, Daya M.; Macri, Lucas M.; Mould, Jeremy R.; Huchra, John P.; Freedman, Wendy L.; Kennicutt, Robert C.; Ferrarese, Laura; Ford, Holland C.; Graham, John A.; Harding, Paul; Han, Mingsheng; Hill, Robert J.; Hoessel, John G.; Hughes, Shaun M. G.; Illingworth, Garth D.; Madore, Barry F.; Phelps, Randy L.; Saha, Abhijit; Sakai, Shoko; Silbermann, Nancy A.; Stetson, Peter B. |
| Abstract | We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accuracy. Sixty-nine Cepheids with periods in the range 9-60 days were observed over 12 epochs using the F555W filter, and over four epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent packages, DAOPHOT II/ALLFRAME and DoPHOT. Period-luminosity relations in the V and I bands were constructed using 36 fairly isolated Cepheids present in our set of 69 variables. Extinction-corrected distance moduli relative to the LMC of 10.63 +/- 0.09 and 10.56 +/- 0.10 mag were obtained using the ALLFRAME and DoPHOT data, respectively. True distance moduli of 29.13 +/- 0.18 and 29.06 +/- 0.18 mag, corresponding to distances of 6.3 +/- 0.7 and 6.1 +/- 0.7 Mpc, were obtained by assuming values of μ0 = 18.50 +/- 0.10 mag and E(V - I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by AURA, Inc. under NASA contract NAS 5-26555. |
