HST/WFC3 UVIS detectors: radiation damage effects and mitigation

Abstract

Devices in low Earth orbit are particularly susceptible to the cumulative effects of radiation damage and the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS detectors, installed on HST in May 2009, are no exception. Such damage not only generates new hot pixels but also generates charge traps which degrade the charge transfer efficiency (CTE), causing a loss in source flux as well as a systematic shift in the object centroid as the trapped charge is slowly released during readout. Based on an analysis of internal and external monitoring data, we provide an overview of the consequences of the ~3 years of radiation damage to the WFC3 CCD cameras. The advantages and disadvantages of available mitigation options are discussed, including use of the WFC3 post-flash and charge injection modes now available to observers, and the status of an empirical pixel-based correction similar to the one adopted for the HST Advanced Camera for Surveys (ACS).