The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope*

Daya M. Rawson; Lucas M. Macri; Jeremy R. Mould; John P. Huchra; Wendy L. Freedman; Robert C. Kennicutt; Laura Ferrarese; Holland C. Ford; John A. Graham; Paul Harding; Mingsheng Han; Robert J. Hill; John G. Hoessel; Shaun M. G. Hughes; Garth D. Illingworth; Barry F. Madore; Randy L. Phelps; Abhijit Saha; Shoko Sakai; Nancy A. Silbermann; Peter B. Stetson

doi:10.1086/304882

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The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope^*

Daya M. Rawson¹, Lucas M. Macri², Jeremy R. Mould¹, John P. Huchra², Wendy L. Freedman³, Robert C. Kennicutt⁴, Laura Ferrarese⁵, Holland C. Ford^6,7, John A. Graham⁸, Paul Harding⁴, Mingsheng Han⁹, Robert J. Hill¹⁰, John G. Hoessel⁹, Shaun M. G. Hughes¹¹, Garth D. Illingworth¹², Barry F. Madore⁵, Randy L. Phelps³, Abhijit Saha⁷, Shoko Sakai⁵, Nancy A. Silbermann⁵, and Peter B. Stetson¹³

© 1997. The American Astronomical Society. All rights reserved. Printed in U.S.A.
The Astrophysical Journal, Volume 490, Number 2 Citation Daya M. Rawson et al 1997 ApJ 490 517 DOI 10.1086/304882

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Author affiliations

¹ Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, Australian National University, Weston Creek, ACT 2611, Australia

² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138

³ Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101

⁴ Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721

⁵ Infrared Processing and Analysis Center, California Institute of Technology, Mail Stop 100-22, 770 South Wilson Avenue, Pasadena, CA 91125

⁶ Department of Physics and Astronomy, John Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686

⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218

⁸ Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305

⁹ Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706

¹⁰ Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771

¹¹ Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0EZ, England, UK

¹² UCO/Lick Observatory, University of California, Santa Cruz, CA 95064

¹³ Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V8X 4M6, Canada

Dates

Received 1996 September 16
Accepted 1997 June 5

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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.

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Footnotes

*
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.

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