The calibration of the Hubble Space Telescope Kuiper belt object search: Setting the record straight

The limiting magnitude of the Hubble Space Telescope (HST) data set used by Cochran and coworkers in 1995 to detect small objects in the Kuiper belt i s reevaluated, and the methods used are described in detail. It is shown, b y implanting artificial objects in the original HST images and rereducing t he images using our original algorithm, that the limiting magnitude of our images (as defined by the 50% detectability limit) is V = 28.4. This value is statistically the same as the value found in the original analysis. We f ind that similar to 50% of the moving Kuiper belt objects with V = 27.9 are detected when trailing losses are included. In the same data in which thes e faint objects are detected, we find that the number of false detections b righter than V = 28.8 is less than one per WFPC2 image. We show that, prima rily due to a zero-point calibration error. but partly due to inadequacies in modeling the HST's data noise characteristics and Cochran and coworkers' reduction techniques, Brown and coworkers in 1997 underestimated the signa l-to-noise ratio of objects in the HST data set by over a factor of 2, and their conclusions are therefore invalid.