HST Call for Proposals and HST Primer for Cycle 24
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Hubble Space Telescope Primer for Cycle 24 > Chapter 4: Cycle 24 Scientific Instruments > 4.2 Wide Field Camera 3 (WFC3)

4.2
The Wide Field Camera 3 (WFC3) was installed in May 2009 during Servicing Mission 4, replacing the highly accomplished WFPC2. This camera provides ultraviolet, optical, and near-infrared imaging through two independent channels. These channels cannot be operated simultaneously, although they can be operated sequentially within the same orbit. Their location in the HST field of view can be seen in Figure 2.2
The Wide Field Ultraviolet-Visible Channel (WFC3/UVIS) is a high throughput, panchromatic camera with a field of view of 162" x 162", sensitive to wavelengths from 200 nm to 1000 nm. The total system throughput with this camera is 28% at 600 nm (see Figure 4.2). The detector is a pair of butted, 2K by 4K, thinned and backside-illuminated CCDs with an ultraviolet-optimized anti-reflective coating and 15 x 15 μm pixels. The plate scale is 0.04 arcsec/pixel. In addition to wavelength optimization, the primary differences between the WFC3 and ACS CCDs include a lower read noise (3 e- for WFC3, 4 e- for ACS) and a smaller inter-chip gap (465 μm rather than 750 μm). The UVIS channel provides 62 broad-, medium-, and narrow-band filters, and one grism.
The Wide Field High-Throughput Infrared Channel (WFC3/IR) has a 136" x 123" field of view over the wavelength range of 800 nm to 1700 nm. The total system throughput with this camera is 50% at 1600 nm (see Figure 4.2). The detector is a 1K by 1K HgCdTe Teledyne array with 18 x 18 μm pixels. The plate scale is 0.13 arcsec/pixel. The detector has 12 e- RMS read noise in a 16-sample non-destructive readout sequence, or 21 e- RMS read noise in the difference of two samples (a correlated double sample). The IR channel provides 15 broad-, medium-, and narrow-band filters and two grisms.
WFC3 has slitless imaging spectroscopic modes in both channels and five UVIS quad filters as described in Section 4.6.2.
The capability of commanding the UVIS shutter to use exclusively one of the two sides of the shutter blade in short exposures, to avoid vibration and PSF smearing, was implemented early in cycle 22. This option (BLADE=A in APT) will be made available to the observer when it is critical to the scientific success of a program. See Section 6.11.4 in the WFC3 Instrument Handbook.
Starting in Cycle 20, a major new capability was implement: adding a flash at the end of a UVIS exposure (post-flash). Post-flash greatly increases the detection of faint sources in low background observations where CTE losses would otherwise remove much or all of the flux from those sources. Most UVIS observers should consider using post-flash; it is useful for all UV, narrow-band, and relatively short medium- and broad-band exposures where the detection of faint sources is required. It should replace charge injection in essentially all circumstances. Users considering charge injection rather than post-flash should consult STScI via the help desk. Further information on CTE and post-flash is available in the WFC3 Instrument Handbook and at the WFC3 UVIS CTE webpage. Note that, starting in Cycle 23, APT has provided a diagnostic message for UVIS exposures that may have insufficient or excessive flash.
The spatial scanning observing technique was introduced for WFC3 in Cycle 19. This mode can be used to turn stars into well-defined streaks on the detector or to spread a stellar spectrum perpendicular to its dispersion. It is useful for:
See the WFC3 Instrument Handbook and WFC3 ISR 2012-08 for further discussion of spatial scanning.

Hubble Space Telescope Primer for Cycle 24 > Chapter 4: Cycle 24 Scientific Instruments > 4.2 Wide Field Camera 3 (WFC3)

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