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[8.02] Charge Transfer Efficiency of the Wide Field and Planetary Camera 2

I. Heyer, B. Whitmore, S. Casertano, J. Biretta (Space Telescope Science Institute)

Observations of \omega Cen have been used to characterize the Charge Transfer Efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) onboard the Hubble Space Telescope. A set of formulae has been developed to correct for CTE loss, with dependencies on the X and Y positions, the background counts, the brightness of the star, and the time of the observation. The observations indicate that for very faint stars on a very faint background, the CTE loss from the top to the bottom of a chip has increased from about 4% shortly after the cool-down of WFPC2 (April 23, 1994) to roughly 40% in February 1999, presumably as a result of radiation damage in the space environment. In general, typical WFPC2 exposures are much longer than these short calibration images, resulting in higher background which significantly reduces the CTE loss and minimizes the CTE problem for most science exposures.

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