The recent servicing mission to Hubble not only reinvigorated its science program by installing two new instruments Wide Field Camera 3 (WFC3) and Cosmic Origins Spectrograph (COS) and repairing the STIS and ACS instruments, it also is providing valuable scientific and technical information for future Webb users.
Early data from the IR channel of WF3 show excellent performance from HgCdTe detectors very similar to the short wavelength channel of Webb’s NIRCam. Both the quantum efficiency and noise are significantly improved compared to the NICMOS HgCdTe arrays. Combined with the larger format, the overall speed improvement is a factor of twenty. We can anticipate even larger gains with the larger Webb mirror and larger NIRCam arrays (2x4). The scientific results are stunning, revealing dozens of objects with photometric redshifts z ~ 7-8. If the luminosity functions and densities do not evolve dramatically, Webb should be capable of detecting faint galaxies at the AB ~ 31 level at twice the redshift.
The ACS repair was enabled by replacing the WF CCD readout hardware with a Webb ASIC (clocking, readout, and digitizer). The ASIC has lowered the CCD readout noise to almost single electron levels, enchancing the science results and also revealing small signal patterns from the ASIC itself. By studying the ACS darks, NIRCam and NIRSpec scientists will learn how to detect and remove these small data irregularities.
Relevant studies: