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B. Granett, A. Mahabal, S.G. Djorgovski (CalTech), DPOSS Team
With the advent of synoptic sky surveys, 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 the Digital Palomar Observatory Sky Survey (DPOSS) plate overlaps. DPOSS reaches r ~21 mag and has large sky coverage making it well suited to explore variability at visible wavelengths. Approximately 40% of the northern sky was imaged at least twice in all of the 3 DPOSS bands (gri), with the time baseline of the observations ranging from nights to years. We have mined roughly 5000 deg2 in gri for highly variable and transient sources. Spectroscopic follow-up observations have been made at the Palomar 200-inch telescope of 40 highly variable sources, revealing a diverse group of AGN (~35%, of which a half are radio loud), cataclysmic variables (~20%), flaring M dwarfs (~20%), early-type stars (~ 5%), and the remaining objects having featureless continuum spectra, which are likely to be blazars. We also searched for optical transients (PSF-like sources detected only once, with a high S/N). We find a surface density of ~1 transient per 10 deg2. These sources may represent a mix of diverse phenomena such as AGN or variable stars where the faint state is below our detection threshold; some may be gamma ray burst orphan afterglows. Follow-up observations of these sources are planned. The results of this pilot project are suggestive of what larger synoptic sky surveys such as Palomar-Quest, Pan-STARRS, or LSST will have to offer.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.