A technique for ultrahigh-precision CCD photometry

We present techniques for wide-field ultrahigh-precision time-sampled CCD p hotometry. Representing a survey of field stars, our data consist of UBVRI photometry and a V-band time series of exposures on 5 consecutive nights co vering 11,500 stars in a similar to1 deg(2) field. The resulting light curv es reach precisions of 0.0020 mag per exposure in the brightest stars (V si milar to 14). Light curves binned and averaged over 4.5 hr reach precisions of 0.00019 mag for the brightest stars. We present example light curves an d discuss one application for surveys of this type: the search for transits by extrasolar planets.