NOAO >   Observing Info >   Approved Programs >   2007A-0536

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Proposal Information for 2007A-0536


PI: Kem Cook, Lawrence Livermore National Laboratory, kcook@llnl.org
Address: Physics Department, 7000 East Ave, Livermore, CA 94550, USA

CoI: Michael Gregg, IGPP - LLNL
CoI: Lucas Macri, NOAO
CoI: Jeremy Mould, NOAO
CoI: Peter Stetson, DAO
CoI: Doug Welch, McMaster University
CoI: David Alves, UC Davis

Title: A Cepheid Distance to the Coma Cluster

Abstract: We have been awarded 180 orbits of \em HST time to discover Cepheids in \gla and \glb, two spiral galaxies located in the Coma Cluster, with the goal of obtaining a direct measurement of the Hubble constant without relying on secondary distance indicators. We request two nights of Kitt Peak 4-m time and two nights of WIYN 3.5-m time to characterize certain systematic uncertainties of the HST measurements. We will use the Kitt Peak 4-m telescope to acquire medium- resolution spectroscopy of \ionH2 regions to characterize the abundance gradient in the target galaxies and estimate the metallicity of the Cepheids. We will use the WIYN 3.5-m telescope to calibrate the instantaneous zeropoint of our HST/ACS photometry to an accuracy of 1% in the V and I bands. These observations play a critical role in reducing our error budget and enabling the first-ever Cepheid-based measurement of H_0 in the Hubble flow.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



NOAO >   Observing Info >   Approved Programs >   2007A-0536

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