1.3 Key Features of WFC3

The optical design of WFC3 features two independent channels, one sensitive at ultraviolet (UV) and optical wavelengths, approximately 200 to 1000 nm (the UVIS channel), and the other sensitive at near-infrared (near-IR) wavelengths, approximately 800 to 1700 nm (the IR channel). A channel-selection mirror directs on-axis light from the HST optical telescope assembly (OTA) to the IR channel, or the mirror can be removed from the beam to allow light to enter the UVIS channel. This means that simultaneous observations with the UVIS and IR detectors are not possible. However, both UVIS and IR observations can be made sequentially, even during the same HST orbit. 

The extended wavelength range, combined with high sensitivity, high spatial resolution, a large field of view, and a wide selection of spectral elements, makes WFC3 an extremely versatile instrument. Key features of WFC3 include:

• UVIS channel: two 2k × 4k CCDs; pixel scale 0.04 arcsec/pix; field of view 162 × 162 arcsec; wavelength range 200-1000 nm; S/N=10 in a 10-hour exposure (F606W filter) for a point source with V=29.2 (ABMAG).
• IR channel: 1k × 1k HgCdTe array; pixel scale 0.13 arcsec/pix; field of view 136 × 123 arcsec; wavelength range 800-1700 nm; S/N=10 in a 10-hour exposure (F160W) for a point source with H=27.9 (ABMAG).
• 62 wide-, medium-, and narrow-band filters in the UVIS channel.
• 15 wide-, medium-, and narrow-band filters in the IR channel.
• 1 grism in the UVIS channel (G280), and 2 grisms in the IR channel (G102 and G141).

In 2001, a “white paper” was prepared by the SOC and the Science IPT(see Acknowledgments for list of members). This report outlined some scientific areas anticipated to especially benefit from the capabilities of WFC3. These included searches for galaxies at redshifts up to z~10; studies of the physics of star formation in distant and nearby galaxies; investigations of resolved stellar populations down to faint levels in the UV, optical, and near-IR; and high-resolution imaging of objects in the solar system. Since installation, WFC3’s panchromatic capabilities have allowed investigations of the assembly and evolution of galaxies; star birth, evolution, and death and its relation to the interstellar medium; individual and collective properties of small solar system bodies; and aurorae and meteorology of the outer planets. This report (Stiavelli, M., & O’Connell, R.W., eds., 2000, “Hubble Space Telescope Wide Field Camera 3, Capabilities and Scientific Program”) can be found at: http://www.stsci.edu/~WFC3/resources/WFC3-WhitePaper-2001.pdf

WFC3 provides some overlapping capabilities with the near-infrared instruments on the James Webb Space Telescope (JWST). Both offer observing modes in the 0.6-1.7 um range. When considering which observatory to utilize, observers should consider their scientific requirements: (A) limiting sensitivity; (B) limiting spatial and spectral resolution; (C) temporal coverage and field of regard; (D) specific filters/bandpasses/grism modes; (E) scanning speed; (F)  other efficiency factors as needed.

A brief review for observers considering differences between the observatories can be found in the JWST documentation: Guidelines for Proposals where JWST and HST Overlap in Capabilities. See Section 3.3.5 for a comparison of JWST/NIRCAM and WFC3 throughputs.