NOAO >   Observing Info >   Approved Programs >   2003A-0075

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Proposal Information for 2003A-0075


PI: Abhijit Saha, NOAO, saha@noao.edu
Address: 950 N. Cherry Ave, Tucson, AZ 85726, USA

CoI: Brad Whitmore, STScI
CoI: Andrew Dolphin, NOAO
CoI: Peter Stetson, DAO
CoI: Stefano Casertano, STScI
CoI: Ralph Bohlin, STScI

Title: Faint Photometric Standard Fields for HST and Large Ground-Based Telescopes

Abstract: Some of the most important projects with the most expensive telescope ever built - HST - are hostage to the uncertainty in the absolute calibration of its photometric system. The standard practice in the past has been to calibrate faint objects (i.e., V ~ 26) observed with long exposures against bright stars (V ~ 13) observed with very short exposures. There is now good evidence that non- linearities in the detectors are the main cause of uncertainty in the absolute photometric accuracy of WFPC2 on HST. We are using the Mini- Mosaic Imager on the WIYN telescope to obtain observations of faint standards (V ~ 22) for carefully chosen fields that have already been observed with WFPC2. This will allow us to \it retroactively recover the history of the absolute calibration of WFPC2 throughout its mission , and hence improve the available photometric accuracy for all WFPC2 observations. These newly defined standard fields can also serve as the basis for calibrating ACS and WFC3 throughout their missions, as well as for 8m class ground based telescopes. This will greatly reduce the error budgets for a wide variety of fundamental projects (e.g., extragalactic Cepheids and RR Lyrae stars; supernovae; globular-cluster ages; metallicity estimates, ...).


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



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