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J. A. Newman, M. Davis (UC Berkeley), S. Zepf (Yale), W. L. Freedman (Carnegie Institute), N. A. Silbermann (IPAC), R. Phelps (Oberlin), B. F. Madore (IPAC), P. Stetson (DAO)
In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope on 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (6 orbits) in the F814W filter. This galaxy lies within the "Cen30" portion of the Centaurus cluster, which is concentrated around a redshift of \approx 3000 km/sec. Previous distance estimates for this cluster have varied significantly and presented disagreements with studies of large-scale structure, motivating our investigation. NGC 4603 is the most distant galaxy in which a search for Cepheids has been conducted. Using our WFPC2 observations, we have found a number of candidate Cepheid variable stars; however, at such faint magnitudes, magnitude measurement errors may lead to apparent variability of significant amplitude in intrinsically nonvarying stars. We have examined this effect through detailed simulations, and by means of a maximum likelihood analysis obtain limits on the distance of NGC 4603.
The author(s) of this abstract have provided an email address for comments about the abstract: jnewman@astro.berkeley.edu