The WSDS Multiframe Pipeline processing generates a Working Database (WDB) that contains extractions of all "sources" detected on the coadded (L3a) images, and characterized on both the coadded and individual Single-exposure (L1) images. In second-pass processing for the All-Sky Data Release, the multiband source detection threshold is set to SNR>3.5, deeper than the required level required for the All-Sky Catalog to insure the completeness of the Catalog. As a result, the fractional reliability of the WDB (e.g. the ratio of the number of detections of real sources of astrophysical infrared emission to the number of all source extractions) is less than required for the Source Catalog (>99.9% for SNR>20; see VI.6). In addition to extractions of real astrophysical sources, the WDB contains:
The Source Selection criteria for WISE All-Sky Release Source Catalog, described below, are designed to draw from the WDB the subset of rows that constitute a reliable Catalog with accurate photometry and positions that also satisfies the completeness objectives of the survey (>95% for SNR>20). Entries in the WDB are selected for inclusion in the Source Catalog if they meet all of the criteria listed below.
All-Sky Source WDB entries that do not meet all of the following criteria are excluded from the Source Catalog, and are instead listed in the All-Sky Reject Table. Thus, the WISE All-Sky Release Source Catalog and Reject Table taken together contain all of the entries from the Source WDB produced by second-pass Multiframe Pipeline processing.
The position of a WDB entry must be >50" from the boundary of the Atlas Image from which it was extracted to be included in the All-Sky Release Source Catalog. The purpose of this safety boundary is to eliminate entries that may have incorrect aperture photometry in the largest measurement aperture, which has 50" radius.
For this purpose, the distance to an Atlas Image boundary is given by the coadd pixel coordinates of a source (wx, wy). Atlas Images are 4095x4095 pixels in size and the coadd pixel scale is 1.375"/pix. Thus, the edge boundary criterion requires a source to have pixel coordinates in the range
Because of the overlap between Atlas Tiles, any source will usually fall more than 50" from the edge of at least one Tile.
To be included in the Source Catalog, an All-Sky Source WDB entry must have what is considered a high-quality, reliable detection in at least one WISE band. A reliable detection in a band is defined as meeting all of the following criteria in that band. Note that if a WDB entry satisfies all of these criteria in a band, it will be included in the Catalog even if the detections in other bands do not satisfy the criteria.
A reliable band-detection in the All-Sky Source WDB must have a valid detection in the band (e.g not a 2σ upper limit) and that detection must have have SNR>5. The detection validity and SNR measurement is required to be from the profile-fit photometry.
The SQL expression of the reliability selection criterion is:
where "?" is the band, 1, 2, 3 or 4.
Note that the Catalog may contain sources with measurements that have SNR≤5 in one or more bands that are pulled along by detections in other band(s) that have SNR>5.
To filter out spurious detections of image artifacts caused by bright sources, a reliable source band-detection is one that is not flagged as a spurious detection of an artifact in the band. Spurious detections of artifacts are flagged by having a capital letter value in the cc_flags parameter. The SQL expression of this requirement is:
where "?" is the band, 1, 2, 3 or 4.
The Catalog may contain sources that are flagged as spurious detections of image artifacts in one or more bands as long as there is a non-flagged detection in another band that meets all other selection criteria.
A reliable band-detection in the WDB must have been extracted from a region with a minimum depth-of-coverage of at least five independent frames. The SQL expression of this requirement is:
where "?" is the band, 1, 2, 3 or 4.
This requirement is designed to eliminate spurious detections in low coverage areas within Atlas Tiles. Because they do not persist on the sky, transient events such as cosmic ray strikes, residual satellite trails, hot pixel events and scattered light from very bright moving objects such as the moon and planets are usually suppressed by pixel outlier rejection during the image coaddition process. However, outlier rejection becomes ineffective when four or fewer frames are available for coaddition, and single-frame transients can persist into the coadds and induce spurious detections.
The Catalog may contain sources that are measured on fewer than five frames on one or may bands as long as there is a reliable detection in another band that meets all other selection criteria.
Mars, Jupiter and Saturn are among the brightest mid-infrared sources observed by WISE. They produce a significant number of spurious source extractions associated with their diffractions spikes, scatter light halos, optical ghosts and latent images. Because the planets are so bright, and because they moved during the WISE observations, they were not uniquely detected nor were their fluxes measured accurately during Multiframe Processing. Consequently, the automated artifact identification processing subsystem could not flag spurious detections of these artifacts. Therefore, the spurious detections would not be filtered from the Catalog by the requirement on the cc_flags parameter listed above.
Spurious extractions associated with Mars, Jupiter and Saturn were identified by visually examining the positions of Multiframe Pipeline WDB extractions that meet all other Catalog selection criteria on the Atlas Images surrounding the planets. Extractions that could not be reliably associated with images of compact astronomical sources in any band were identified, and the resulting list of spurious detections were then filtered from the Catalog. This was the only manual filtering applied to the WISE All-Sky Source Catalog. These manually excluded extractions are in the Reject Table.
The numbers of spurious extractions around each planet that were identified and excluded from the Catalog are listed in Table 1. Also provided in Table 1 are links to lists of the spurious extractions associated with each planet, identified by the cntr value of the extraction in the Reject Table.
| Planet | No. of Extractions | Extraction Table |
|---|---|---|
| Mars | 11518 | X |
| Jupiter | 15330 | X |
| Saturn | 3683 | X |
Last update: 2012 March 16