4.5 Wide Field and Planetary Camera 2 (WFPC2)

The WFPC2 has three "wide-field" CCDs and one high-resolution (or "planetary") CCD. Each CCD covers 800 x 800 pixels and is sensitive from 1150 to 11,000 Å. All four CCDs are exposed simultaneously, with the target of interest being placed as desired within the FOV.

The three Wide Field Camera (WFC) CCDs are arranged in an "L"-shaped FOV whose long side projects to 2.5', with a projected pixel size of 0.10" (see Figure 2.2). The Planetary Camera (PC) CCD has a FOV of 35" x 35", and a projected pixel size of 0.0455". The WFC configuration provides the larger FOV, but undersamples the cores of stellar images; the PC configuration samples the images better, but has the smaller FOV.

A total of 48 different filters may be inserted into the optical path. Polarimetry may be performed by placing a polarizer quad filter into the beam and exposing through the different quads and/or different filter wheel rotations. There are a total of 18 narrow-band and medium-band filters, as well as 2 narrow-band quad filters that each yield 4 different central wavelengths. There are also 4 linear ramp filters that effectively allow you to image a ~ 10" region in an arbitrary 1.3% bandpass at any wavelength between 3700Å and 9760Å, by means of a variety of filter wheel orientations and target placements within the FOV.

Beginning in 2003 a serious electronic anomaly appeared in the WF4 CCD detector of WFPC2 wherein sporadic images have corrupted (but correctable) photometry. The frequency and severity of the problem increased slowly, and by late 2005 a significant fraction of images taken in WF4 were blank and unusable. Early in 2006 a work-around was found which allowed good data to be taken even though the WF4 electronics continued to slowly fail. As of this writing we expect WF4 to continue to produce good data for several more years, but there is some possibility the hardware failure might accelerate with WF4 being completely lost. The other three CCDs appear unaffected, and in fact small targets are usually placed on the PC1 or WF3 CCDs, so the WF4 anomaly has had much less impact than it otherwise might have. Large targets and surveys do benefit from the added sky area contributed by WF4, and would be more impacted by its failure. In addition, some specialized filters (polarizers, ramps, quad filters) rely on WF4 and would be severely impacted, were it to fail completely.