The snapshot survey: A search for gravitationally lensed quasars with the Hubble Space Telescope

In a systematic attempt to find new examples of multiply imaged quasars that are the result of gravitational lensing, 89 short exposures, through two filters, of high-luminosity quasars from a well-defined sample have been obtained with the Hubble Space Telecope's Planetary Camera. Useful high-resolution images of approximately 30 quasars have resulted. None of the quasars show evidence of multiple images due to gravitational lensing. Simulations show that multiple images with brightness ratios of up to several magnitudes would have been detected, down to image separations of ≈0″1. These results are compared with lower resolution ground-based surveys and current theoretical predictions. The Snapshot Survey has uncovered several engineering problems in the observatory's performance, some of which have already been corrected. In particular, we find that the large telescope pointing errors and drift rates are primarily the result of the lack of correction for stellar aberration when pointing and tracking are performed solely with gyroscopes. The implications of the possibly low intrinsic gyro drift rate on future observations are briefly discussed.