The source selection process draws the subset of extractions from the 6x point and extended source WDBs that meet the reliability goals of the 6x-PSC and 6x-XSC while maintaining the completeness objectives of the deeper observations. The selection criteria used for the 6x-PSC and 6x-XSC are similar to those used for the All-Sky PSC and XSC, and users should refer to V.3 for detailed descriptions.
A graphical illustration of 6x-PSC and 6x-XSC source selection process results is given in Figure 1 of A3.6.a.
i. 6x-PSC Selection Criteria
Sources in the 6x Point Source WDB must satisfy the criteria described in Table 1 to be included in the 6x-PSC. These differ from the criteria used to construct the All-Sky PSC in three ways:
Category | Criteria | Purpose |
---|---|---|
Scan-Edge Boundaries | Source lies >10" from edge of 6x scan | Exclude detections on or near scan edges for which brightness and/or position cannot be accurately measured |
SNR and Band-detection | Source must have a valid measurement in at least one band
(rd_flg="1","2" or "3"),
AND [Have SNR>7 in at least one
detected band The SNR thresholds can be satisfied by either the SNR derived from the photometric measurement uncertainty ([jhk]_msig), or the scan SNR ([jhk]_snr) |
To filter out low SNR noise excursion detections |
Artifacts | Source must not be identified as a detection of an image artifact produced by a bright star in any band according to the cc_flg. | Spurious source rejection |
Frame-detection | Sources brighter than J<15.9, H<14.8 or Ks<14.4
mag must be measurable on at least two out of the six (and sometimes seven)
frames sampling their positions
AND [must be detected at SNR>3 on at least 40% of the available frames, 6x point source frame detection statistics are tabulated in the ndet column. |
Rejection of transients such as hot pixels, cosmic rays and residual meteor trails |
Point Source Profile | Non-saturated Read_2 sources with SNR<10 that are measured
using profile-fit photometry (rd_flg='2')
must have a 2 goodness-of-fit
value [jhk]_psfchi < 2
in at least one detected band.
Bright sources that saturate the Read_2 exposures and non-saturated Read_2 detections with SNR>10 are not required to satisfy this criterion. The latter exception avoids rejecting bright multiple stars and galaxies. |
Rejection of transients such as hot pixels, cosmic rays and residual meteor trails |
Multiply-Detected Sources | For sources in Tile overlap regions that are detected more than once, the detection farthest from its scan edge is selected. If a source in an overlap region is detected only once, it is always included in the 6x-PSC. (see A3.6.d) | To eliminate redundant detections. |
ii. 6x-XSC Selection Criteria
Sources in the 6x Extended Source WDB must satisfy the criteria described in Table 2 to be included in the 6x-XSC. There are two differences between the source selection for the 6x-XSC and All-Sky XSC:
Category | Criteria | Purpose |
---|---|---|
Scan-Edge Boundaries | Source lies >15" from edge of 6x scan | Exclude detections on or near scan edges for which brightness and/or position cannot be accurately measured |
SNR | Source must have SNR>7 in at least one
band.
This threshold can be satisfied by the SNR derived from uncertainties on either the 7" circular aperture photometry, ([jhk]_msig_7), or the Ks=20 mag arcsec-2 elliptical isophotal photometry ([jhk]_msig_k20fe). |
To filter out sources with low confidence extended classifications |
Artifacts | Source must not be identified as a spurious detection of an image artifact produced by a bright star or as a piece of a large, bright galaxy according to the cc_flg | Spurious source rejection |
Extended Classification | Source must have:
0 < e_score < 1.5 OR 0 < g_score < 1.5 See Section IV.5 for a description of the "Oblique Decision Tree" classifier which is used to determine the e_score and g_score values for candidate extended sources. |
To reject "false" extended sources such as multiple stars and low SNR point sources |
Multiply-Detected Sources | For sources in Tile overlap regions that are detected more than once, the detection farthest from its scan edge is selected. If a source in an overlap region is detected only once, it is always included in the 6x-XSC. (see A3.6.d) | To eliminate redundant detections. |
[Last Updated: 2006 November 10; by R. Cutri]