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Description
During the final months of 2MASS observatory operations, a campaign of targeted "long exposure" observations was carried out during times when no previously unscanned parts of the sky were available for the main survey. These observations used the same freeze-frame scanning technique employed for the survey, but with READ2-READ1 exposures six times longer than was used for normal survey observations (hence they are referred to as "6x" observations). The 2MASS 6x measurements were intended to probe ~1 magnitude deeper than the main survey in unconfused regions.
Approximately 590 deg2 of sky distributed in 30 targeted regions were scanned at least once using the long exposures. Most of this area is concentrated in two large, comprehensive surveys of the Large and Small Magellanic Clouds, 383 deg2 and 127 deg2, respectively. Twenty-eight additional smaller fields were mapped in the 6x mode from both observatories, covering targets that include the Pleiades open cluster, galactic star formation complexes, M31, nearby galaxy clusters and the Lockman Hole.
Data processing produced a 6x Image Atlas and 6x point and extended source Working Databases (6x-PSWDB and 6x-XSWDB), analogous to those from the main survey. "Catalogs" of point and extended source detections (6x-PSC and 6x-XSC) that represent uniform, higher reliability single-epoch snapshots of the near infrared sky were drawn from the 6x WDBs using SNR and quality criteria similar to those used to construct the All-Sky Release PSC and XSC (A3.6.c). The 6x-PSC and 6x-XSC have not received the same level of scrutiny and validation as the 2MASS All-Sky PSC and XSC, though.
Unlike the All-Sky Release Catalogs, the 6x Catalogs are not released as separate tables. The 6x Point and Extended Source Catalogs are instead integrated into the respective 6x Point and Extended Source WDBs. Sources comprising the Catalogs are denoted in the WDBs with the cat flag, and have cat="1".
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