AAS 196th Meeting, June 2000
Session 32. Space Instrumentation
Display, Tuesday, June 6, 2000, 10:00am-6:30pm, Empire Hall South

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[32.09] Charge Transfer Efficiency in the WFPC2 CCD Arrays

J. Biretta, A. Riess, S. Baggett, B. Whitmore, S. Casertano, I. Heyer, A. Schultz, S. Gonzaga, M. Wiggs, M. McMaster, C. O'Dea, A. Koekemoer (Space Telescope Science Institute)

We present an overview of Charge Transfer Efficiency (CTE) issues in the WFPC2 CCDs, including results of recent on-orbit tests, and advice on mitigating CTE effects on photometry. New studies using hotpixels, cosmic rays, and residual images as probes of CTE have revealed at least four distinct components of CTE losses. The largest effect appears related to trapping and release of charge on timescales of hundreds of milliseconds during the readout process. This is manifest as tails on images which extend for dozens of pixels in the Y-direction (parallel register direction) on the CCDs, which have the effect of robbing counts from typical small apertures used for photometry. There is considerable evidence now for a quasi-linear increase in CTE effects with time, due to on-going radiation damage to the CCD arrays in the harsh space environment. We review empirical results on stellar photometry, and preliminary results of new tests on extended targets (faint galaxies). We suggest observational strategies for reducing the impact of CTE, and photometric corrections which can be applied during data analysis.

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