NASA's Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) mapped the sky at 3.4, 4.6, 12, and 22 μm (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 5σ 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 μm bands were acquired, but elevated thermal emission from the telescope prevented useful data from being collected in the 22 μm band. As illustrated in Figures 1 and 2, the 3-Band Cryo 3.4 and 4.6 μm band measurements are nearly as sensitive as those in the full cryogenic survey, but the increasing temperature and reduced exposure times of the 12 μm measurements result in significantly lower sensitivity.
The WISE 3-Band Cryo Data Release incorporates data taken between August 6 and September 29, 2010. Release data products include an Atlas of 5,649 match-filtered, calibrated and coadded image sets, a Source Working Database containing positions and 3-band photometry for over 261 million sources detected on the Atlas Images, and this Explanatory Supplement that describes the format content, characteristics and cautionary notes for the 3-Band Cryo Release products. The Release products were generated through second-pass processing using the WISE Science Data System that benefited from improvements to calibration, processing parameters and algorithms that were made to produce the WISE All-Sky Data Release.
Because of the dynamic characteristics of the WISE telescope and detectors during the 3-Band Cryo mission phase, and because these data did not receive the same level of scrutiny as those from the full cryogenic survey, the 3-Band Cryo products should be used with some care. You are strongly encouraged to review the Cautionary Notes for the WISE 3-Band Cryo Release data products to best utilize them in your research.
The WISE All-Sky Data Release remains the best compendium of sources of mid-infrared emission over the entire sky. Because the 3-Band Cryo Release data provide independent, second epoch measurements for 30% of the sky, they are best used as a resource to learn more about objects found in the All-Sky Release Atlas and Catalog. The 3-Band Cryo Source Working Database can be used to test for proper motion and flux variability of All-Sky Catalog sources. The reliability of faint sources can be verified if they appear in the 3-Band Cryo Images, particularly in the W1 and W2 bands where sensitivity is similar in both mission phases. Finally, the 3-Band Cryo Images and Database can provide information in regions that have low coverage in the All-Sky Release products.
|Figure 1 - Montage comparing 12'x12' sections of Single-exposure images covering the same field near the south ecliptic pole taken during the full cryogenic and 3-Band Cryo survey phases. The top, middle and bottom rows show W1, W2 and W3 images, respectively. The first column shows images taken on 24 March 2010 UTC during the full cryogenic survey phase. Columns two through five show 3-Band Cryo survey phase images taken on 8 August, 14 August, 20 August and 18 September 2010 UTC when the W3 exposure times were 8.8 sec, 4.4 sec, 2.2 sec and 1.1 sec, respectively. The W1 and W2 exposure times are 7.7 sec for all survey phases.|
|Figure 2 - Comparison of Atlas Images from the All-Sky Release (left) and 3-Band Cryo Release (right) of the central 12'x12' region of Tile 0450p605 that contains the core of the IC 1848 star formation region. The frame depth-of-coverage is similar in both survey phases. All of the W3 frames that were coadded to make the 3-Band Cryo W3 Atlas Image were taken with 1.1 sec exposure times.|
Last Updated: 2012 July 24