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A. Mahabal, B. Granett, S.G. Djorgovski, R. Brunner (Palomar Observatory, Caltech), R.R. Gal (JHU), S.C. Odewahn (ASU), P. Lopes (Palomar Observatory, Caltech), R.R. de Carvalho (Observatorio Nacional, Brazil), DPOSS Team
Exploration of the time variability on the sky at all flux levels and all wavelengths is rapidly becoming a new frontier of astronomical research. We report on the results of a preliminary study, based on the regions of the sky multiply imaged in DPOSS plate overlaps. Approximately 40% of the northern sky was imaged at least twice in each of the 3 DPOSS bands, with time baselines extending to a couple of years. Reaching down to ~21 mag, this is a unique data set with which to explore the variability of the sky at visible wavelengths. In this pilot project, we covered over 2000 deg2 in all 3 DPOSS bands (roughly Gunn gri). We used an automated procedure to find highly variable objects from the overlap regions of DPOSS plate catalogs. A number of candidates were identified, and some were followed up spectroscopically at Palomar. They include a diverse group of AGN, cataclysmic variables, and possibly other types of objects. A number of other interesting objects have been found serendipitously over the years in the course of DPOSS work including a candidate for a GRB ``orphan afterglow'', normal stars undergoing so-called mega-flares, etc. This work illustrates the great potential for studies of the variability on the sky using systematic, digital sky surveys.
Cataloging of DPOSS was supported in part by a generous gift from the Norris Foundation. Software development work was supported in part by grants from NASA. BG acknowledges a SURF fellowship.
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