WSA Browser

Glossary of WSA attributes

This Glossary alphabetically lists all attributes used in the UKIDSSDR5 database(s) held in the WSA. If you would like to have more information about the schema tables please use the UKIDSSDR5 Schema Browser (other Browser versions).

A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z

Y

Name Schema Table Database Description Type Length Unit Default Value Unified Content Descriptor

y UKIDSSDetection WSA Y coordinate of detection real 4 pixels POS_PLATE_Y

y dxsDetection, dxsListRemeasurement, gcsDetection, gcsListRemeasurement, gpsDetection, gpsListRemeasurement, lasDetection, lasListRemeasurement, udsListRemeasurement WSA Y coordinate of detection {catalogue TType keyword: Y_coordinate}
Intensity-weighted isophotal centre-of-gravity in Y. real 4 pixels POS_PLATE_Y

y ptsDetection WSATransit Y coordinate of detection {catalogue TType keyword: Y_coordinate}
Intensity-weighted isophotal centre-of-gravity in Y. real 4 pixels POS_PLATE_Y

y udsDetection WSA Y coordinate of detection (SE: Y_IMAGE) {catalogue TType keyword: Y_coordinate}
Intensity-weighted isophotal centre-of-gravity in Y. real 4 pixels POS_PLATE_Y

y_coadd twomass_xsc 2MASS y (in-scan) position (coadd coord.). real 4 arcsec INST_POS

Y_IMAGE mgcDetection MGC Object y position real 4 pixel

Y_OFF mgcGalaxyStruct MGC Y offset of Galaxy Centre real 4 99.99

Y_OFFm mgcGalaxyStruct MGC Y offset error (-) real 4 99.99

Y_OFFp mgcGalaxyStruct MGC Y offset error (+) real 4 99.99

yAperMag3 gcsPointSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Default point/extended source Y aperture corrected mag (2.0 arcsec aperture diameter) real 4 mag -0.9999995e9 PHOT_MAG

yAperMag3 gcsSource, lasSource WSA Default point/extended source Y aperture corrected mag (2.0 arcsec aperture diameter)
If in doubt use this flux estimator real 4 mag -0.9999995e9 PHOT_MAG

yAperMag3Err gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in default point/extended source Y mag (2.0 arcsec aperture diameter) real 4 mag -0.9999995e9 ERROR

yAperMag4 gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Extended source Y aperture corrected mag (2.8 arcsec aperture diameter) real 4 mag -0.9999995e9 PHOT_MAG

yAperMag4Err gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in extended source Y mag (2.8 arcsec aperture diameter) real 4 mag -0.9999995e9 ERROR

yAperMag6 gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Extended source Y aperture corrected mag (5.7 arcsec aperture diameter) real 4 mag -0.9999995e9 PHOT_MAG

yAperMag6Err gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in extended source Y mag (5.7 arcsec aperture diameter) real 4 mag -0.9999995e9 ERROR

yCen Detection SSA Intensity-weighted Y-centroid of image float 8 microns POS_PLATE_Y

yClass gcsPointSource, gcsSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA discrete image classification flag in Y smallint 2 -9999 CLASS_MISC

yClassStat gcsPointSource, gcsSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA N(0,1) stellarness-of-profile statistic in Y real 4 -0.9999995e9 STAT_PROP

yDeblend gcsPointSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA placeholder flag indicating parent/child relation in Y int 4 -99999999 CODE_MISC

yDeblend gcsSource, lasSource WSA placeholder flag indicating parent/child relation in Y int 4 -99999999 CODE_MISC

This CASU pipeline processing source extraction flag is a placeholder only, and is always set to zero in all passbands in the merged source lists. If you need to know when a particular image detection is a component of a deblend or not, test bit 4 of attribute ppErrBits (see corresponding glossary entry) which is set by WFAU's post-processing software based on testing the areal profiles aprof2-8 (these are set by CASU to -1 for deblended components, or positive values for non-deblended detections). We encode this in an information bit of ppErrBits for convenience when querying the merged source tables.

yEll gcsPointSource, gcsSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA 1-b/a, where a/b=semi-major/minor axes in Y real 4 -0.9999995e9 PHYS_ELLIPTICITY

yeNum gcsMergeLog, gcsZYJHKmergeLog, lasMergeLog WSA the extension number of this Y frame tinyint 1 NUMBER

yeNum lasYJHKmergeLog WSA the extension number of this frame tinyint 1 NUMBER

yErr UKIDSSDetection WSA Error in Y coordinate real 4 pixels ERROR

yErr dxsDetection, dxsListRemeasurement, gcsDetection, gcsListRemeasurement, gpsDetection, gpsListRemeasurement, lasDetection, lasListRemeasurement, udsListRemeasurement WSA Error in Y coordinate {catalogue TType keyword: Y_coordinate_err}
Estimate of centroid error. real 4 pixels ERROR

yErr ptsDetection WSATransit Error in Y coordinate {catalogue TType keyword: Y_coordinate_err}
Estimate of centroid error. real 4 pixels ERROR

yErr udsDetection WSA Error in Y coordinate (SE: ERRY2_IMAGE^½) {catalogue TType keyword: Y_coordinate_err}
Estimate of centroid error. real 4 pixels ERROR

yErrBits gcsPointSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA processing warning/error bitwise flags in Y int 4 -99999999 CODE_MISC

yErrBits gcsSource, lasSource WSA processing warning/error bitwise flags in Y int 4 -99999999 CODE_MISC

Apparently not actually an error bit flag, but a count of the number of zero confidence pixels in the default (2 arcsec diameter) aperture.

yEta gcsPointSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Offset of Y detection from master position (+north/-south) real 4 arcsec -0.9999995e9 POS_EQ_DEC_OFF

yEta gcsSource, lasSource WSA Offset of Y detection from master position (+north/-south) real 4 arcsec -0.9999995e9 POS_EQ_DEC_OFF

When associating individual passband detections into merged sources, a generous (in terms of the positional uncertainties) pairing radius of 2.0 (UKIDSS LAS and GPS; also non-survey programmes) or 1.0 (UKIDSS GPS, DXS and UDS) arcseconds is used, the higher value enabling pairing of moving sources when epoch separations may be several years. Such a large association criterion can of course lead to spurious pairings in the merged sources lists (although note that between passband pairs, handshake pairing is done: both passbands must agree that the candidate pair is their nearest neighbour for the pair to propagate through into the merged source table). In order to help filter spurious pairings out, and assuming that large positional offsets between the different passband detections are not expected (e.g. because of source motion, or larger than usual positional uncertainties) then the attributes Xi and Eta can be used to filter any pairings with suspiciously large offsets in one or more bands. For example, for a clean sample of QSOs from the LAS, you might wish to insist that the offsets in the selected sample are all below 1 arcsecond: simply add WHERE clauses into the SQL sample selection script to exclude all Xi and Eta values larger than the threshold you want.

yGausig gcsPointSource, gcsSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA RMS of axes of ellipse fit in Y real 4 pixels -0.9999995e9 MORPH_PARAM

yHallMag gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Total point source Y mag real 4 mag -0.9999995e9 PHOT_MAG

yHallMagErr gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in total point source Y mag real 4 mag -0.9999995e9 ERROR

yMag gcsSourceRemeasurement, lasSourceRemeasurement WSA Y mag (as appropriate for this merged source) real 4 mag -0.9999995e9 PHOT_MAG

yMagErr gcsSourceRemeasurement, lasSourceRemeasurement WSA Error in Y mag real 4 mag -0.9999995e9 ERROR

ymax Detection SSA Topmost extent of image on plate float 8 microns POS_PLATE_Y

ymfID gcsMergeLog, gcsZYJHKmergeLog, lasMergeLog WSA the UID of the relevant Y multiframe bigint 8 ID_FRAME

ymfID lasYJHKmergeLog WSA the UID of the relevant multiframe bigint 8 ID_FRAME

ymin Detection SSA Bottommost extent of image on plate float 8 microns POS_PLATE_Y

ymj gcsSourceRemeasurement, lasSourceRemeasurement WSA Default colour Y-J (using appropriate mags) real 4 mag PHOT_COLOR

ymj_1Ext lasExtendedSource, lasPointSource, lasYJHKsource, reliableLasPointSource WSA Extended source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

ymj_1Ext lasSource WSA Extended source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymj_1ExtErr lasExtendedSource, lasPointSource, lasYJHKsource, reliableLasPointSource WSA Error on extended source colour Y-J real 4 mag -0.9999995e9 ERROR

ymj_1ExtErr lasSource WSA Error on extended source colour Y-J real 4 mag -0.9999995e9 ERROR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymj_1Pnt lasExtendedSource, lasPointSource, lasYJHKsource, reliableLasPointSource WSA Point source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

ymj_1Pnt lasSource WSA Point source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymj_1PntErr lasExtendedSource, lasPointSource, lasYJHKsource, reliableLasPointSource WSA Error on point source colour Y-J real 4 mag -0.9999995e9 ERROR

ymj_1PntErr lasSource WSA Error on point source colour Y-J real 4 mag -0.9999995e9 ERROR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymjErr gcsSourceRemeasurement, lasSourceRemeasurement WSA Error on colour Y-J real 4 mag ERROR

ymjExt gcsPointSource, gcsZYJHKsource, reliableGcsPointSource WSA Extended source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

ymjExt gcsSource WSA Extended source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymjExtErr gcsPointSource, gcsZYJHKsource, reliableGcsPointSource WSA Error on extended source colour Y-J real 4 mag -0.9999995e9 ERROR

ymjExtErr gcsSource WSA Error on extended source colour Y-J real 4 mag -0.9999995e9 ERROR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymjPnt gcsPointSource, gcsZYJHKsource, reliableGcsPointSource WSA Point source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

ymjPnt gcsSource WSA Point source colour Y-J (using aperMag3) real 4 mag -0.9999995e9 PHOT_COLOR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

ymjPntErr gcsPointSource, gcsZYJHKsource, reliableGcsPointSource WSA Error on point source colour Y-J real 4 mag -0.9999995e9 ERROR

ymjPntErr gcsSource WSA Error on point source colour Y-J real 4 mag -0.9999995e9 ERROR

Default colours from pairs of adjacent passbands within a given set (e.g. Y-J, J-H and H-K for YJHK) are recorded in the merged source table for ease of querying and speedy querying via indexing of these attributes. Presently, the point-source colours and extended source colours are computed from the aperture corrected AperMag3 fixed 2 arcsec aperture diameter measures (for consistent measurement across all passbands) and generally good signal-to-noise. At some point in the future, this may be changed such that point-source colours will be computed from the PSF-fitted measures and extended source colours computed from the 2-d Sersic model profile fits.

yObjID gcsPointSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA DEPRECATED (do not use) bigint 8 -99999999 ID_NUMBER

yObjID gcsSource, gcsSourceRemeasurement, lasSource, lasSourceRemeasurement WSA DEPRECATED (do not use) bigint 8 -99999999 ID_NUMBER

This attribute is included in source tables for historical reasons, but it's use is not recommended unless you really know what you are doing. In general, if you need to look up detection table attributes for a source in a given passband that are not in the source table, you should make an SQL join between source, mergelog and detection using the primary key attribute frameSetID and combination multiframeID, extNum, seqNum to associate related rows between the three tables. See the Q&A example SQL for more information.

yPA gcsPointSource, gcsSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA ellipse fit celestial orientation in Y real 4 Degrees -0.9999995e9 POS_POS-ANG

yPetroMag gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Extended source Y mag (Petrosian) real 4 mag -0.9999995e9 PHOT_MAG

yPetroMagErr gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in extended source Y mag (Petrosian) real 4 mag -0.9999995e9 ERROR

yPixSize CurrentAstrometry WSATransit Angular size of pixels in Y real 4 Arcseconds -0.9999995e9 POS_ANG_DIST_GENERAL

yPixSize CurrentAstrometry, PreviousAstrometry WSA Angular size of pixels in Y real 4 Arcseconds -0.9999995e9 POS_ANG_DIST_GENERAL

yPnt Plate SSA Centre of scan area in Y real 4 microns POS_PLATE_Y

yPos nvssSource NVSS Y position (Dec direction) of the radio source real 4 pixels POS_CCD_Y

yppErrBits gcsPointSource, gcsSourceRemeasurement, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSourceRemeasurement, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA additional WFAU post-processing error bits in Y int 4 0 CODE_MISC

yppErrBits gcsSource, lasSource WSA additional WFAU post-processing error bits in Y int 4 0 CODE_MISC

Post-processing error quality bit flags assigned (NB: from UKIDSS DR2 release onwards) in the WSA curation procedure for survey data. From least to most significant byte in the 4-byte integer attribute byte 0 (bits 0 to 7) corresponds to information on generally innocuous conditions that are nonetheless potentially significant as regards the integrity of that detection; byte 1 (bits 8 to 15) corresponds to warnings; byte 2 (bits 16 to 23) corresponds to important warnings; and finally byte 3 (bits 24 to 31) corresponds to severe warnings:

Byte Bit Detection quality issue Threshold or bit mask Applies to

Decimal Hexadecimal

0 4 Deblended 16 0x00000010 LAS, GCS, GPS, DXS

0 6 Bad pixel(s) in default aperture 64 0x00000040 LAS, GCS, GPS, DXS

2 16 Close to saturated 65536 0x00010000 LAS, GCS, GPS

2 19 Possible crosstalk artefact/contamination 524288 0x00080000 LAS, GCS, DXS

2 22 Lies within a dither offset of the stacked frame boundary 4194304 0x00400000 LAS, GCS, GPS, DXS

In this way, the higher the error quality bit flag value, the more likely it is that the detection is spurious. The decimal threshold (column 4) gives the minimum value of the quality flag for a detection having the given condition (since other bits in the flag may be set also; the corresponding hexadecimal value, where each digit corresponds to 4 bits in the flag, can be easier to compute when writing SQL queries to test for a given condition). For example, to exclude all K band sources in the LAS having any error quality condition other than informational ones, include a predicate ... AND kppErrBits ≤ 255. See the SQL Cookbook and other online pages for further information.

yPsfMag gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Point source profile-fitted Y mag real 4 mag -0.9999995e9 PHOT_MAG

yPsfMagErr gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in point source profile-fitted Y mag real 4 mag -0.9999995e9 ERROR

ySeqNum gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA the running number of the Y detection int 4 -99999999 ID_NUMBER

ySeqNum gcsSourceRemeasurement, lasSourceRemeasurement WSA the running number of the Y remeasurement int 4 -99999999 ID_NUMBER

ySerMag2D gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Extended source Y mag (profile-fitted) real 4 mag -0.9999995e9 PHOT_MAG

ySerMag2DErr gcsPointSource, gcsSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Error in extended source Y mag (profile-fitted) real 4 mag -0.9999995e9 ERROR

ySize MultiframeDetector WSA Corresponding image size (Y); value only available if catalogue file exists {catalogue extension keyword: NYOUT} int 4 -99999999 NUMBER

ySize MultiframeDetector WSATransit Corresponding image size (Y); value only available if catalogue file exists {catalogue extension keyword: NYOUT} int 4 -99999999 NUMBER

yXi gcsPointSource, gcsZYJHKsource, lasExtendedSource, lasPointSource, lasYJHKsource, reliableGcsPointSource, reliableLasPointSource WSA Offset of Y detection from master position (+east/-west) real 4 arcsec -0.9999995e9 POS_EQ_RA_OFF

yXi gcsSource, lasSource WSA Offset of Y detection from master position (+east/-west) real 4 arcsec -0.9999995e9 POS_EQ_RA_OFF

When associating individual passband detections into merged sources, a generous (in terms of the positional uncertainties) pairing radius of 2.0 (UKIDSS LAS and GPS; also non-survey programmes) or 1.0 (UKIDSS GPS, DXS and UDS) arcseconds is used, the higher value enabling pairing of moving sources when epoch separations may be several years. Such a large association criterion can of course lead to spurious pairings in the merged sources lists (although note that between passband pairs, handshake pairing is done: both passbands must agree that the candidate pair is their nearest neighbour for the pair to propagate through into the merged source table). In order to help filter spurious pairings out, and assuming that large positional offsets between the different passband detections are not expected (e.g. because of source motion, or larger than usual positional uncertainties) then the attributes Xi and Eta can be used to filter any pairings with suspiciously large offsets in one or more bands. For example, for a clean sample of QSOs from the LAS, you might wish to insist that the offsets in the selected sample are all below 1 arcsecond: simply add WHERE clauses into the SQL sample selection script to exclude all Xi and Eta values larger than the threshold you want.

WFAU, Institute for Astronomy,
Royal Observatory, Blackford Hill
Edinburgh, EH9 3HJ, UK
Tel +44 131 668 8356 (office)
or +44 131 668 8100 (switchboard)

wsa-support@roe.ac.uk
30/04/2009