NOAO >   Observing Info >   Approved Programs >   2001A-0070

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Proposal Information for 2001A-0070


PI: Brad Whitmore, Space Telescope Science Institute, whitmore@stsci.edu
Address: 3700 San Martin Dr., Baltimore, MD 21218, USA

CoI: Abi Saha, 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 propose to use 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. Future HST observations of the new fields would allow us to follow WFPC2's absolute calibration to the end of its mission, and could later serve as the basis for calibrating ACS and WFC3. 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, ...).


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