PI: Tim Axelrod, Univ of Arizona and LSST Corp, firstname.lastname@example.org
Address: Steward Observatory, 933 N Cherry, Tucson, AZ 85721, USA
CoI: Edward Olszewski, University of Arizona
CoI: Abi Saha, NOAO
CoI: Jay Holberg, University of Arizona
Title: How to reach sub-1% photometry in an all-sky survey such as LSST
Abstract: Proposed all-sky surveys wish to have photometry on an energy-based system (AB magnitudes, for instance). Two important projects requiring such photometry are luminosity distances of supernovae and high quality photometric redshifts. In order to achieve sub-1% energy-based photometry, hot DA White Dwarfs (WDs) with spectroscopically determined T_eff and log(g) and model-atmosphere spectral-energy distributions (SEDs) are needed as standards. What is not known is exactly how to use these WDs as standards most correctly. We do not know how quickly in angular distance and time the atmospheric conditions of a program star observation and standard observation, even with extinction applied, become different enough to turn sub-1% photometry into the more normal 1.5-2% standard star solutions typically derived for a night. This knowledge is critical in understanding how many faint standards need to be set up, and in planning a strategy for calibrating a large survey such as LSST. In our June observing run at Mt Bigelow we saw short-term ~1% changes from the normal secant-airmass extinction. ``Normal photometry'' with CCDs is not designed to detect such changes, and will compromise the creation of surveys both accurate and precise to less than 1%.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360