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VIII. Post-Cryo Data Release

1. Introduction

The 2013 NEOWISE Post-Cryo Data Release is comprised of data taken during the four month period following the complete exhaustion of cryogens in the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) payload. During this period, known as the NEOWISE Post-Cryo mission phase, data were collected by the 3.4 and 4.6 μm detectors at sensitivities similar to those achieved during the full cryogenic phase. WISE scanned approximately 70% of the sky during the Post-Cryo phase, completing a survey of the inner Main Asteroid Belt and a second coverage of the inertial sky.

WISE is a NASA Astrophysics Division Medium Class Explorer mission that conducted a sensitive mid-infrared imaging survey of the entire sky in 2010 and 2011. WISE mapped the sky with a 40 cm telescope and camera equipped with four 1kx1k array detectors that imaged the same 47'x47' field-of-view at 3.4, 4.6, 12, and 22 μm (W1, W2, W3 and W4) simultaneously. The WISE telescope, optics and detectors were cooled by a two-stage solid hydrogen cryostat. WISE surveyed the sky 1.2 times between January 7 and August 6 2010, during its full cryogenic mission phase, when both inner and outer cryogen tanks held hydrogen ice and all detectors operated at full sensitivity. Data collected during this phase make up the March 2012 All-Sky Data Release, which is the best compendium of information about the static mid-infrared sky. WISE continued to survey an additional 30% of the sky between 6 August and 29 September 2010 UTC, the 3-Band Cryo phase, using the W1, W2 and W3 detectors after the hydrogen ice sublimated in the outer cryogen tank, but while the detectors were still cooled by cryogen in the inner tank. Data collected during this phase comprised the June 2012 supplemental 3-Band Cryo Data Release.

The NEOWISE Post-Cryo mission phase began on 29 September 2010 UTC after the solid hydrogen in the inner cryogen tank was exhausted and the focal plane assemblies, optics and telescope gradually warmed to approximately 73.5 K. The W1 and W2 HgCdTe detectors remained fully operational during this time with sensitivities close to those observed in the cryogenic mission phases (Figures 1 and 2), although the number of high noise pixels increased as the detectors warmed. No useful data were collected by the W3 and W4 Si:As detectors that were above their operating temperatures and were saturated by thermal emission from payload. WISE surveyed approximately 70% of the sky in the Post-Cryo mission phase until 1 February 2011 UTC when data collection was halted.

NEOWISE Post-Cryo mission and initial data processing operations were funded by the NASA Planetary Division as part of the NEOWISE program (Mainzer et al. 2011 ApJ, 731, 53). The Post-Cryo observations enabled the survey of the inner Main Asteroid Belt to be completed (Figure 3), and the search for candidate solar system objects with the WISE Moving Object Pipeline System (WMOPS) to be continued. WISE also finished a complete second coverage of the inertial sky during this period. Although the sensitivity to asteroids and comets was reduced by the loss of the W3 and W4 detectors during the Post-Cryo period, WMOPS identified and reported 10,158 tracklets to the IAU Minor Planet Center (MPC), corresponding to 6545 confirmed objects. Of those, discovery of 1064 is attributed to WISE, including 12 new Near Earth Objects. Among the most interesting of the NEOWISE discoveries from the Post-Cryo phase was that of 2010 TK7, the first Earth Trojan asteroid (Conners, M. et al. 2011, Nature, 475, 481).

The 2013 NEOWISE Post-Cryo Data Release consists of products that were generated during a complete second-pass reprocessing of the Post-Cryo survey phase data that was funded by a grant from the NASA ROSES Near Earth Object Observation program. This reprocessing utilized calibrations that were optimized for the performance of the warmer detectors and telescope during the Post-Cryo mission phase, and contains source extractions down to a much lower flux level than the earlier processing. The Post-Cryo Data Release products include over 900,000 W1 and W2 Single-exposure images and a database of over 7.3 billion source detections extracted from those images. These products provide the best individual flux measurements for solar system objects that were identified by WMOPS during the Post-Cryo survey, and they enable follow-up of inertial sources found in the WISE All-Sky Release Catalog to investigate time-dependent properties such as flux variability and proper motion. The Post-Cryo Release does not include coadded Atlas Images or a deep source detection Working Database like the All-Sky and 3-Band Cryo Releases. However, the Post-Cryo Single-exposure images will be combined with those the full-cryogenic and 3-Band Cryo phases to provide the deepest WISE observations as part of the AllWISE program. You are strongly encouraged to review the Cautionary Notes for the Post-Cryo Release data products to best utilize them in your research.

The NEOWISE Post-Cryo Preliminary Data Release made on July 31, 2012, is superseded by the 2013 Post-Cryo Release. The products in the Preliminary release were generated during first-pass data processing that took place while WISE was still acquiring data. First-pass processing used early reduction algorithms and calibrations that were not yet optimized for the characteristics of the warmer telescope and detectors. The preliminary processing was intended to provide quality assessment to support survey operations and input for WMOPS that identified and reported candidate moving object tracklets to the MPC within 10 days of their observation for timely ground-based recovery and confirmation.

  3/24/2010 9/30/2010 2/1/2011
Figure 1 - Montage comparing sections of Single-exposure images covering the same 12'x12' field near the south ecliptic pole taken during the full cryogenic and Post-Cryo survey phases. The top and bottom rows show W1 and W2 images, respectively. The first column shows images taken on 24 March 2010 UTC during the full cryogenic survey phase. Columns two and three Post-Cryo survey phase images taken on 30 September 2010 and 1 February 2011 UTC, the beginning and end of the Post-Cryo period. The scan directions are different on the three dates, and the images sample different parts of the W1 and W2 focal plane detectors.

Figure 2 - Color-magnitude diagrams (CMD) for Single-exposure source measurements in a 2°x2° region centered on l,b=161.6°,+32.4°. The left panel shows the CMD from the Post-Cryo Release Single-exposure Source Database and the right panel shows the CMD from the All-Sky Release Single-exposure Source Database. The Post-Cryo detections reach a comparable depth in W1 as the full-cryo detections, but the width of the stellar locus at brighter magnitudes indicates that the photometric precision is slightly poorer.

Figure 3 - Top-down view of the Solar System showing the position of all objects detected by the WISE Moving Object Pipeline System (WMOPS) on 1 February 2011. The grey circles indicate the orbits of the planets out to Jupiter. The small black points are Main Belt, Trojan, Greek and Hilda asteroids. The filled red and green circles are Near Earth asteroids; the green circles are WISE discoveries. The filled cyan and yellow squares are comets; the yellow squares are WISE discoveries. The dashed red line indicates the points up to which WISE surveyed at the end of the full-cryogenic survey phase. The arc with lower density of points in the Main Belt marks the region surveyed during the WISE 3-Band Cryo and NEOWISE Post-Cryo phases.

Last Updated: 2013 April 8

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