Calibration Status and Results for Wide Field Camera 3

Wide Field Camera 3 (WFC3) is a general-purpose imager in development for installation in HST Servicing Mission 4 (SM4). Covering the wavelength range of 200-1700 nm in two observing channels, WFC3 offers powerful new capabilities, particularly in the near-ultraviolet and near-infrared bands. During 2004, the instrument was integrated and underwent a substantial suite of end-to-end characterization and performance tests. In this paper, we present a brief overview of the design and scientific purpose of WFC3, summarize the results of its test program to date, and highlight some recent developments in detector technology that will further enhance the performance of WFC3’s IR channel. 1. Design and Purpose of WFC3 The WFC3 program originated in 1997 when NASA decided that the target date for the end of the HST mission would be moved from 2005 to 2010. Recognizing that this date would place HST’s complement of imagers beyond their nominal design lifetimes, the HST Project initiated the development of a new camera to ensure and extend HST’s imaging capabilities into those later years. WFC3 was thus conceived, to be developed as a facility instrument on behalf of the astronomical community (that is, with no PI team and no Guaranteed Time Observations). Day-to-day scientific guidance is provided by a Science Integrated Product Team from NASA/GSFC and STScI, with broad guidance exercised by a community-based Science Oversight Committee, chaired by R. O’Connell of the University of Virginia. As problems with NASA’s shuttle program have delayed the planned SM4 until at least late 2007 (with end-of-mission in ≈2013), the need for a backup camera for HST has, if anything, increased, but WFC3 provides much more than imaging “insurance” for Hubble. WFC3 is a powerful scientific imager in its own right, offering unique capabilities and scientific potential, particularly in the near-ultraviolet (NUV) and near-infrared (NIR) bands (very nicely complementary to the I-band-optimized Advanced Camera for Surveys). WFC3 features two channels. The UV/Visible (UVIS) channel covers 200-1000 nm and is based on a two-CCD mosaic (4096×4096 total pixels). The CCDs are low-noise, UV-enhanced devices manufactured by e2v (formerly Marconi), yielding an unprecedented combination of sensitivity and field of view for NUV imaging with HST. The UVIS channel offers a 160×160 arcsec field with 0.039 arcsec pixels, with a rich assortment of broad, medium, and narrowband filters and a UV grism. The IR channel (800-1700 nm) incorporates a custom HgCdTe focal plane array (FPA), developed by Rockwell Scientific Company, with 1014×1014 imaging pixels. The novel 1700 nm cutoff of this array permits low-dark-current operation at temperatures that can be reached with WFC3’s passive radiator and thermo-electric cooling, and minimizes the impact of thermal background radiation from the relatively warm HST environment. The IR channel covers a field of 139×123 arcsec at ≈0.130 arcsec sampling, also with a sizable