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Description
NASA's Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) mapped the sky at 3.4, 4.6, 12, and 22 um (W1, W2, W3, W4) in 2010 with an angular resolution of 6.1", 6.4", 6.5", & 12.0" in the four bands. During the full cryogenic survey phase, 7 January 2010 to 6 August 2010, when the detectors and telescope were cooled by solid hydrogen in both inner and outer cryogen tanks, WISE achieved 5 sigma point source sensitivities better than 0.08, 0.11, 1 and 6 mJy in unconfused regions on the ecliptic in the four bands. The sky was covered 1.2 times during this period, and the data acquired were used to construct the products for the March 2012 WISE All-Sky Data Release.
The WISE 3-Band Cryo survey phase began on 6 August 2010 following the exhaustion of frozen hydrogen in the payload's outer cryogen tank. WISE scanned approximately 30% of the sky over the next 54 days while the focal planes were cooled by hydrogen ice in the inner cryogen tank. The telescope warmed from the 12 K maintained during the main mission to 45 K. Imaging data in the 3.4, 4.6 and 12 um bands were acquired, but elevated thermal emission from the telescope prevented useful data from being collected in the 22 um band. As illustrated in Figures 1 and 2, the 3-Band Cryo 3.4 and 4.6 um band measurements are nearly as sensitive as those in the full cryogenic survey, but the increasing temperature and reduced exposure times of the 12 um measurements result in significantly lower sensitivity.
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