|Space Telescope Science Institute|
|WFC3 Instrument Handbook|
The science return on any data can typically be enhanced if observers acquire a basic understanding of how the detectors operate, and of their individual characteristics and limitations. For the most demanding observations, such as imaging very faint or extremely bright sources, or for exposures using non-default parameters, an even deeper understanding of the detectors and their operation may be required. This chapter aims to provide both basic and in-depth information on the detectors used in both WFC3 channels. Sections 5.2-5.4 discuss the CCD detectors used in the UVIS channel, and Sections 5.5-5.7 discuss the infrared detector used in the IR channel.Table 5.1 summarizes the basic characteristics of the flight CCD and IR detectors. For the CCDs, the information is either an average for the two chips, or the range of values for both of them. Results are based on ground measurements as well as on-orbit data acquired during 2009 and 2010 after WFC3 was installed in HST.Table 5.1: WFC3 Detector Characteristics
2 butted 2051 × 4096, 1024 × 1024 (1014 × 1014 active) 15 μm × 15 μm 18 μm × 18 μm Rhomboidal, 162" × 162" Rectangular, 136" × 123" 50–59% @ 250 nm1
68–69% @ 600 nm
~5.5 e–/hr/pixel (median, Aug. 2013), increasing ~0.5 e–/hr/pixel/year 0.048 e–/s/pixel (median) 20.2–21.4 e– (pair of reads)12.0 e– (16-read linear fit) Full Well2 77,900 e– (mean saturation level) 1.55 e–/DN 2.28–2.47 e–/ADU −83°C Quantum efficiency at 250 nm does not include multiple-electron events, which lead to larger apparent efficiency in e.g., Figure 5.2.The IR full well value is based on fully-integrated instrument ground testing. Other CCD and IR parameters are derived from on-orbit data.