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VII. 3-Band Cryo Data Release

2. 3-Band Cryo Data Products

a. Source Working Database


  1. Column Descriptions
  2. Contents and Usage of the WDB
  3. General Properties
  4. Photometric Properties
  5. Astrometric Properties

The WISE 3-Band Cryo Source Working Database (WDB) contains astrometry and photometry for 261,418,479 sources detected on the 3-Band Cryo Atlas Intensity Images. Positions, magnitudes, astrometric and photometric uncertainties, flags indicating the quality of the source characterizations, and associations with the WISE All-Sky Release Catalog and the 2MASS Point and Extended Source Catalog sources are presented for each source.

A summary of the properties of the 3-Band Cryo WDB and detailed column descriptions are presented below. More detailed descriptions of photometric and astrometric characteristics of the WDB are presented in section VII.5. Descriptions of processing algorithms used to generate the WDB can be found in sections IV and VII.3.

Users are strongly encouraged to read the Cautionary Notes before using the 3-Band Cryo Source WDB.

i. Column Descriptions

ii. Contents and Usage of the WDB

The 3-Band Cryo Source WDB contains measurements of all detections made on the coadded Atlas Images during second-pass Multiframe Pipeline processing. The database is analogous to the one generated from the Multiframe processing of the full cryogenic mission data. However, the 3-Band Cryo WDB has not been split into a separate Catalog and Reject Table, as was done for the All-Sky Data Release.

Consequently, the 3-Band Cryo WDB is not a well-vetted list of reliable mid-infrared source detections like the WISE All-Sky Release Catalog. The WDB contains detections of real astrophysical sources, along with low SNR noise excursions, spurious detections of image artifacts and transient pixel events, and duplicate, redundant entries of source detections in Atlas Tile overlap regions. The general reliability of the 3-Band Cryo WDB is described in VII.5.e. Tips for selecting reliable and unique detections the the WDB are given in VII.1.d.iii.

As is the case with the All-Sky Release Catalog, the reliable detections in the 3-Band Cryo WDB are not restricted to point sources such as stars and unresolved galaxies. The WDB contains point-like objects, close multiple sources, detections on the disks and spiral arms of resolved galaxies and clumps or filaments in Galactic nebulosity. Many of the objects that are well-resolved with respect to the WISE PSF are identified by having extended source flag values of ext_flg=1.

The 3-Band Cryo WDB is best used as as a source of supplemental information for objects that are found in the WISE All-Sky Release Source Catalog. Because the 3-Band Cryo observations provide independent, second-epoch of measurements of approximately 30% of the sky, the WDB can be used to search for potential proper motions and flux variability of All-Sky Catalog sources. The reliability of a faint source from the All-Sky Catalog can be verified if it appears in the 3-Band Cryo WDB, particularly for those with detections in W1 and W2 where the sensitivity is close to the full-cryo mission phase. Finally, the 3-Band Cryo WDB provides potential source information for regions with low or even no-coverage in the All-Sky Catalog. To facilitate such comparisons, the 3-Band Cryo WDB and All-Sky Release Catalog have been positionally cross-correlated, and the the identification, position offsets and 4-band magnitudes of the closest Catalog entry within 3 arcseconds are included in each 3-Band Cryo WDB source record.

iii. General Properties

iv. Photometric Properties

v. Astrometric Properties

The astrometric quality of the 3-Band Cryo WDB is described in VII.5.c. Because position reconstruction is based primarily on W1 detections that have similar sensitivity in the 3-Band Cryo observations, the absolute accuracy of 3-Band Cryo WDB astrometry is comparable to that of the All-Sky Release Catalog (VI.4). Bright, non-saturated sources in the 3-Band Cryo WDB have position residuals <0.2 arcsec with respect to the 2MASS Point Source Catalog, and the residual increases to approximately 0.4 arcsec for SNR~20 sources.

The relative agreement between astrometry in the 3-Band Cryo WDB and All-Sky Release Catalog is slightly better than the absolute accuracy which makes the WDB a resources for searching for candidate high proper motion objects. An example of this is illustrated in Figure 6 that shows the RA and Dec position differences in the 3-Band Cryo WDB and All-Sky Release Catalog plotted as function of 3-Band Cryo W1 magnitude for isolated, point-like sources in a 4 deg2 region centered on the position of Teegarden's star (α,δ=43.2643°+16.8701°). The green curves show ±5 times the RMS of the average position residuals. Teegarden's star RA and Dec residuals, as derived from the 3-Band Cryo WDB r_allsky and pa_allsky values, are indicated by the large blue points. The WISE-measured proper motion is 5.36 arcsec/year measured over the 195 days separating the All-Sky Release Catalog and 3-Band Cryo WDB observations, slightly larger than the published motion of 5.05 arcsec/year (Lepine and Shara, 2005, AJ, 129, 1483).

Figure 6 - RA and Dec differences reported for the same sources in the WISE 3-Band Cryo WDB and All-Sky Release Catalog in the 4 deg2 region centered on Teegarden's star. Black points are non-blended sources (nb=1) that are not flagged as extended (ext_flg=0), The green lines show ±5 times the RMS of the average position residuals. The position residuals for Teegarden's star from the 3-Band Cryo WDB are the large blue points.

Last Updated: 2012 July 26

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