Performance of the CFH12K: a 12K by 8K CCD mosaic camera for the CFHT prime focus

Abstract

CFH12K is a 12,288 by 8,192 pixel wide-field imaging camera in operation at the 3.6m Canada-France-Hawaii Telescope (CFHT) since January 1999. It still remains the largest close-packed array in use in astronomy today. The mosaic consists of twelve MIT Lincoln laboratories 2K by 4K thinned backside illuminated CCID-20 devices. The camera is used in broad-band and narrow-band filter direct imaging mode which constrains the devices' operating parameters to ensure the best data quality. Adaptation to the 20-year old CFHT prime focus environment included modifications to reduce the scattered light seen by the camera. Computer facilities have been upgraded and new software has been developed to handle the large amount of data generated. The two terabytes of scientific data taken by the camera in 1999 has proven the success of CFHT's new capability for 42 by 28 square arcminute imaging with high resolution subarcsecond seeing.

The 12K×8K CCD mosaic camera for the Palomar Transient Factory

“…As reported by CFHT [2] , the detectors have an average readout noise of 5 electrons (with a correlated double sampling time of 1 µs per dwell), a dark current of only ~1 electron per minute per pixel at -89 deg. C, and a peak quantum efficiency of up to 90% in R band.…”

“…The remaining three are made from high-resistivity bulk silicon (Hi-Rho) and are grouped in one corner of the mosaic. The Hi-Rho devices have a higher QE (up to 20% more) in the red part of the spectrum, and produce less fringing than the EPI devices due to their larger thickness [2] .…”

“…Although the CCDID-20 CCDs have two outputs, some of the devices have only one functional [2] . Since readout must be synchronous, all CCDs must therefore be read through a single output.…”

“…The cooling of the camera was provided by an 8-liter liquid nitrogen tank. There was also an Auxiliary Control Electronic module, which served as interface to the shutter, filter wheel and temperature control, in coordination with the CCD controllers [2] .…”

“…Our total delivered image quality goal, 2 arcsec, maps to 2 pixels (at 1 arcsec/pixel) [4] , whereas the typical 0.6 arcsec FWHM images on CFHT mapped to 3 pixels at their 0.2 arcsec/pixel plate scale [2] . In combination this placed a tighter requirement on flatness of the CCD surfaces.…”