Candidate Cepheid Variables in the Coma Cluster

Details Candidate Cepheid Variables in the Coma Cluster Candidate Cepheid Variables in the Coma Cluster

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5508c&link_type=abstract

American Astronomical Society, AAS Meeting #211, #55.08; Bulletin of the American Astronomical Society, Vol. 39, p.827

Astronomy and Astrophysics

Astronomy

Scientific paper

In HST cycle 15, we began an 180 orbit project using the Advanced Camera for Surveys Wide Field Camera to search for and phase Cepheid variables in two spiral galaxies in the core of the Coma cluster. This effort ended in late January, 2007 with the death of the ACS. At that point we had collected 4 epochs of observations for NGC 4911 and 5 epochs for NGC 4921 in F606W and 2 and 3 epochs in F814W.All epochs consisted of five orbit visits. These data represented significantly fewer than the needed twelve epochs to effectively phase Cepheid variables. With ACS/WFC, S/N=5-10 or better can be reached for Cepheids with periods of 40d to 70d at mean light in one of our F606W epochs if H0 is approximately 70 km/s/Mpc. The data in-hand allow us to identify resolved stars and variables with colors appropriate for Cepheids. We will present color-magnitude diagrams for these galaxies and candidate Cepheid variables. We have also begun collecting Hα images and spectra using KPNO's WIYN and 4-m telescopes to determine the metallicity of the Cepheids’ environments, which will be presented.
With future ACS or WF3 observations to complete this project a direct application of the canonical primary distance indicator (Cepheid variables) at 100 Mpc will measure the far-field Hubble constant free of many of the systematic uncertainties which beset current determinations relying on secondary indicators. Establishing the far-field Ho with Cepheids will provide one of the strongest links in the extragalactic distance scale, directly calibrate the fiducial fundamental plane of elliptical galaxies in Coma, and provide stronger constraints on the equation of state of the universe as obtained from WMAP results.
KHC's and MDG's work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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