Appendix 4. Calibration Scan Working Databases and Images

3. Calibration Working Databases and Metadata Table Formats

a. Calibration Point Source Working Database Column Descriptions

The following table contains brief descriptions of the parameters provided for each entry in the 2MASS Calibration Point Source Working Databases (Cal-PSWDB, LMC/SMC Cal-PSWDB). The table is organized according to the broad function and utility of the parameters: positional information, photometric information, and source quality information. For Cal-PSWDB and LMC/SMC Cal-PSWDB flag parameters, the meaning of each possible flag value is given, along with some practical information on their usage. The order of the entries in this table is the same as that presented on the IRSA/GATOR query page for this database.

The columns in the following table are:

Column Name: The parameter name in the Cal-PSWDB table. Click on this to go to the section of the Explanatory Supplement where the derivation and/or usage of that parameter is described in more detail.

Format: The ascii-equivalent format of the field in the Cal-PSWDBs, expressed in "C" readable notation. This is useful when parsing the aligned tabular output from IRSA/GATOR. Although the data values will conform to these formats, the actual width of the field in the GATOR output may be padded with extra blank spaces to accommodate column headers. Note that some fields contain null values that will require special handling when parsing Cal-PSWDB tables drawn from IRSA/GATOR output.

Units: The units of the parameter. A value of "---" in this column means that the parameter is dimensionless.

nulls: A "yes" in this column means that this parameter can be null in the Cal-PSWDBs. A "no" means that there will always be a value in this column in the Cal-PSWDBs.

Description: A brief description of the parameter and its values.

Column Name Format Units nulls Description

Primary Positional Information

ra %10.6f deg no J2000 right ascension with respect to the USNOA-2.0 Catalog.
Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy.

dec %10.6f deg no J2000 declination with respect to the USNOA-2.0 Catalog.
Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy.

err_maj %4.2f arcsec no Semi-major axis length of the one sigma position uncertainty ellipse.
A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference.

err_min %4.2f arcsec no Semi-minor axis length of the one sigma position uncertainty ellipse.
A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference.

err_ang %3d deg no Position angle on the sky of the semi-major axis of the position uncertainty ellipse (East of North)

Primary Photometric Information

j_m %6.3f mag yes Default J-band magnitude, or if the source is not detected in the J-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the first character of the rd_flg value (rd_flg[1]). This column is null if the source is nominally detected in the J-band, but no useful brightness estimate could be made (rd_flg[1]="9").

j_cmsig %5.3f mag yes Corrected photometric uncertainty for the default J-band magnitude. If rd_flg[1]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[1]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[1]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If j_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[1]="0" or "6") or if the source is not measurable (rd_flg[1]="9").

j_msigcom %5.3f mag yes Combined, or total photometric uncertainty for the default J-band magnitude. The combined uncertainty is derived from the following relation:

j_msigcom = sqrt(j_cmsig² + j_zperr² + fferr² + [r1normrms²])
where
j_cmsig = Corrected J-band photometric uncertainty
j_zperr = Nightly photometric zero point uncertainty = 0.011 mag
fferr = Flat-fielding residual error = 0.005 mags
r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[1]="1")

This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band).

j_snr %10.1f --- yes J-band "scan" signal-to-noise ratio. This value is given by the ratio of the J-band flux to the characteristic J-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table j_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band).

h_m %6.3f mag yes Default H-band magnitude, or if the source is not detected in the H-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the second character of the rd_flg value (rd_flg[2]). This column is null if the source is nominally detected in the H-band, but no useful brightness estimate could be made (rd_flg[2]="9").

h_cmsig %5.3f mag yes Corrected photometric uncertainty for the default H-band magnitude. If rd_flg[2]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[2]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[2]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If h_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[2]="0" or "6") or if the source is not measurable (rd_flg[2]="9").

h_msigcom %5.3f mag yes Combined, or total photometric uncertainty for the default H-band magnitude. The combined uncertainty is derived from the following relation:

h_msigcom = sqrt(h_cmsig² + h_zperr² + fferr² + [r1normrms²])
where
h_cmsig = Corrected H-band photometric uncertainty
h_zperr = Nightly photometric zero point uncertainty = 0.007 mag
fferr = Flat-fielding residual error = 0.005 mags
r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[2]="1")

This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band).

h_snr %10.1f --- yes H-band "scan" signal-to-noise ratio. This value is given by the ratio of the H-band flux to the characteristic H-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table h_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band).

k_m %6.3f mag yes Default K_s-band magnitude, or if the source is not detected in the K_s-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the third character of the rd_flg value (rd_flg[3]). This column is null if the source is nominally detected in the K_s-band, but no useful brightness estimate could be made (rd_flg[3]="9").

k_cmsig %5.3f mag yes Corrected photometric uncertainty for the default K_s-band magnitude. If rd_flg[3]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[3]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[3]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If k_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[3]="0" or "6") or if the source is not measurable (rd_flg[3]="9").

k_msigcom %5.3f mag yes Combined, or total photometric uncertainty for the default K_s-band magnitude. The combined uncertainty is derived from the following relation:

k_msigcom = sqrt(k_cmsig² + k_zperr² + fferr² + [r1normrms²])
where
k_cmsig = Corrected K_s-band photometric uncertainty
k_zperr = Nightly photometric zero point uncertainty = 0.007 mag
fferr = Flat-fielding residual error = 0.005 mags
r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[3]="1")

This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the K_s-band).

k_snr %10.1f --- yes K_s-band "scan" signal-to-noise ratio. This value is given by the ratio of the K_s-band flux to the characteristic K_s-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table k_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the K_s-band).

Primary Source Quality Information
rel %1s ---- no Reliability flag. Single character flag that is related to the probability that the extraction is a valid detection of a near infrared source on the sky at the time of the observation.

"A" - P>90%

"B" - 80%<P<90%

"C" - 70%<P<80%

"D" - 50%<P<70%

"E" - 20%<P<50%

"F" - P<20%

This flag does not provide information about the quality of the position or flux measurement. For that, users should refer to the ph_qual, rd_flg, cc_flg and positional and photometric uncertainties.

ph_qual %3s --- no
Photometric quality flag. Three character flag, one character per band [JHK_s], that provides a summary of the net quality of the default photometry in each band, as derived from the Read Flag (rd_flg), measurement uncertainties ([jhk]_cmsig), scan signal-to-noise ratios ([jhk]_snr), frame-detection statistics (ndet), and profile-fit reduced chi-squared values ([jhk]_psfchi). The value for ph_qual is set for a band according to the precedence of the table below. For example, a source that is tested and meets the conditions for category "X" is not tested for subsequent qualities.

"X" - There is a detection at this location, but no valid brightness estimate can be extracted using any algorithm. rd_flg="9" and default magnitude is null.

"U" - Upper limit on magnitude. Source is not detected in this band (rd_flg="0"), or it is detected, but not resolved in a consistent fashion with other bands (rd_flg="6"). A value of ph_qual="U" does not necessarily mean that there is no flux detected in this band at the location. Whether or not flux has been detected can be determined from the value of rd_flg. When rd_flg="0", no flux has been detected. When rd_flg="6", flux has been detected at the location where the images were not deblended consistently in all three bands (JHK_s).

"Z" - The detection in this band is positionally associated with the predicted location of an image artifact. The cc_flg value in this band will be C,D,G or P.
"F" - This category includes rd_flg="1" or rd_flg="3" sources where a reliable estimate of the photometric error, [jhk]_cmsig, could not be determined. The uncertainties reported for these sources in [jhk]_cmsig and [jhk]_msigcom are flags and have numeric values >8.0.

"E" - This category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor (rd_flg="2" and [jhk]psf_chi>10.0), or detections where psf fit photometry did not converge and an aperture magnitude is reported (rd_flg="4"), or detections where the number of frames was too small in relation to the number of frames in which a detection was geometrically possible (rd_flg="1" or rd_flg="2").
"A" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>10 AND [jhk]_cmsig<0.10857.

"B" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>7 AND [jhk]_cmsig<0.15510.

"C" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>5 AND [jhk]_cmsig<0.21714.

"D" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with no [jhk]_snr or [jhk]_cmsig requirement.

rd_flg %3s --- no Read flag. Three character flag, one character per band [JHK_s], that indicates the origin of the default magnitudes and uncertainties in each band (j_m,h_m,k_m, j_cmsig, h_cmsig, k_cmsig). Rd_flg values of "1", "2" or "3" generally indicate the best quality detections, photometry and astrometry (although other quality flags must be considered). Values of "0", "4", "6" and "9" in a band indicate either non-detections, or generally poor quality photometry and positions. The definitions of the rd_flg values are:

"0" - Source is not detected in this band. The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20".

"1" - The default magnitude is derived from aperture photometry measurements on the 51 ms "Read_1" exposures. The aperture radius is 4", with the sky background measured in an annulus with an inner radius of 14" and an outer radius of 20". Used for sources that saturate one or more of the 1.3s "Read_2" exposures, but are not saturated on at least one of the 51 ms "Read_1" frames.

"2" - The default magnitude is derived from a profile-fitting measurement made on the 1.3 sec "Read_2" exposures. The profile-fit magnitudes are normalized to curve-of-growth-corrected aperture magnitudes. This is the most common type in the Cal-PSWDBs, and is used for sources that have no saturated pixels in any of the 1.3 sec exposures.

"3" - The default magnitude is derived from a 1-d radial profile fitting measurement made on the 51 ms "Read_1" exposures. Used for very bright sources that saturate all of the 51 ms "Read 1" exposures.

"4" - The default magnitude is derived from curve-of-growth-corrected 4" radius aperture photometry measurements on the 1.3 s "Read_2" exposures. This is used for sources that are not saturated in any of the Read_2 frames, but where the profile-fitting measurements fail to converge to a solution. These magnitudes are the same as the standard aperture magnitudes (j_m_stdap, h_m_stdap, k_m_stdap), but when they are the default magnitudes, it generally implies that they are low quality measurements.

"6" - The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for pairs of sources which are detected and resolved in another band, but are detected and not resolved in this band. This differs from a rd_flg="0" because in this case there is a detection of the source in this band, but it is not consistently resolved across all bands.

"9" - The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for sources that were nominally detected in this band, but which could not have a useful brightness measurement from either profile fitting or aperture photometry. This often occurs in highly confused regions, or very near Tile edges where a significant fraction of the measurement aperture of sky annulus falls off the focal plane.

bl_flg %3s --- no Blend flag. Three character flag, one character per band [JHK_s], that indicates the number of components that were fit simultaneously when estimating the brightness of a source:

"0" - Source is not detected, or is inconsistently deblended in that band.

"1" - One component was fit to the source in R_2 profile-fitting photometry (rd_flg="2"), or default magnitudes are from aperture photometry (rd_flg="1" or "4") or saturated star 1-d radial profile-fitting (rd_flg="3").

">1" - More than one component was fit simultaneously during R2 profile-fit photometry, where the value of the field is the number of components simultaneously fit. The maximum number of components is 7 in any band for the Cal-PSWDBs, so this bl_flg is always a three character flag. Multi-component fitting occurs only for profile-fitting, and only when more than one detection is found within ~5". Single detections that are not well-fit by a single PSF are not split.

cc_flg %3s --- no Contamination and confusion flag. Three character flag, one character per band [JHK_s], that indicates that the extraction is associated with the predicted position of an image artifact, or that the photometry and/or position measurements of a source may be contaminated or biased due to proximity to an image artifact or nearby source of equal or greater brightness. The cc_flg in each band is set in hierarchical order according to the following table, in the event a source is affected by more than one artifact or condition:

"P" = Persistence artifact. Extraction is likely a spurious detection of a latent image left by a nearby bright star.

"G" = Dichroic glint artifact. Extraction is likely a spurious detection of a dichroic glint produced by a nearby bright star.

"C" = Confusion artifact. Extraction is likely a spurious detection in the wings of a nearby bright star.

"D" = Diffraction spike artifact. Extraction is likely a spurious detection on a diffraction spike from a nearby star.

"p" = Persistence. Source may be contaminated by a latent image left by a nearby bright star.

"c" = Photometric Confusion. Source photometry is biased by a nearby star that has contaminated the background estimation. This is very common in high source density regions.

"d" = Diffraction spike confusion. Source may be contaminated by a diffraction spike from a nearby star.

"s" = Electronic stripe. Source measurement may be contaminated by a stripe from a nearby bright star.

"b" = Bandmerge confusion. In the process of merging detections in the different bands for this source, there was more than one possible match between the different band components. This occurs in regions of very high source density, or when multiple sources were split in one band but not another.

"0" = Source is unaffected by known artifacts, or is not detected in the band.

Non-zero values the cc_flg in any band is an indicator that the extraction may be a spurious detection of an image artifact, or that measurements of that source may be contaminated.

ndet %6s --- no Frame detection statistics. A six-character flag, two characters per band [JJHHK_sK_s], that indicates the number frames on which a source was detected, N, and the number of frames on which the source could have been measured, M. The first digit in the pair for each band, N, gives the number of frames on which there were >3 sigma aperture photometry detections of the source. The second digit for each band, M, gives the number of frames on which aperture measurements were possible. Normally, M=6, (occasionally M=7 because the scanning step size was slightly less than 1/6 of the frame size). M can be <6 if frames are "lost" because: a) there were masked pixels within the source aperture due to cosmic ray detections, noisy pixels, meteor trails, etc, or b) there were saturated pixels within the source aperture. Values of M < 6 are not uncommon, but do indicate an effective loss of coverage and sensitivity for a source.
The values of N and M for a band always pertain to the aperture photometry on the 51 ms "Read_1" exposures if rd_flg="1", and to the aperture photometry on the 1.3 s "Read_2" exposures if rd_flg="2" or "4". Sources that are saturated on all of the Read_1 frames (rd_flg="3") have N=0 because no aperture photometry was possible.
Sources with signal-to-noise ratios >8-9 should be detected on all available frames. Values of N < M for such sources are an indication of possible loss of measurement integrity. Values of N < M, or even N=0, are normal for fainter sources because they are too faint on individual frames to yield a >3 sigma detection.

gal_contam %1d --- no Extended source "contamination" flag. A value of gal_contam="2" indicates that this point source falls within the elliptical boundary of an All-Sky XSC source defined by the semi-major axis and ellipticity of the 20 mag arcsec^-2 K_s-band elliptical isophote (r_k20fe) +10%, for XSC sources where r_k20fe is >10''. Sources so indicated are often foreground stars superimposed on background galaxies, or sometimes extractions of pieces of the galaxy or nebula. The point source photometry for these sources is probably contaminated by the surrounding structured extended emission. Point sources can still be superimposed on extended sources and remain unflagged if the XSC source shape is not well-described by an ellipse.
This flag also denotes (gal_contam="1") Cal-PSWDB sources that are equivalent to sources in the XSC, usually the nuclei of galaxies. The Cal-PSWDB gal_contam values correctly flag all point sources that are found to be resolved relative to a single point-spread-function, regardless of extended source size. The gal_contam="1" flagging in the Cal-PSWDB is correct only for XSC sources with r_k20fe >10'' (I.6.b.xii).

"0" - Source does not fall within the elliptical profile of an extended source with semi-major axis >10'', or it is not identified exactly with an Cal-XSWDB source with semi-major axis >10''. However, the source may correspond exactly to a smaller XSC source.

"1" - Source is resolved by 2MASS, and is equivalent to a source in the Cal-XSWDB that has a semi-major axis >10'' in size.
"2" - Source falls within the elliptical boundary of an XSC source that has a semi-major axis >10'' in size.

mp_flg %1d --- no Minor Planet Flag. Indicates if this source is associated with the predicted position of a known minor planet, comet, planet or planetary satellite. This association does not guarantee that the Cal-PSWDB source is a detection of the solar system object.

"0" - Source is not associated with a known solar system object

"1" - Source is associated with the predicted position of a known solar system object. The name and orbital data for the associated objects are given in the Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List. The associated Cal-PSWDB source is cross-referenced in those Lists via the value of pts_key

Additional Positional and Identification Information

pts_key/cntr %10d --- no A unique identification number for the Working Database entry. This column is called pts_key in the DVD-ROM and ftp versions of the Working Databases and cntr in the IRSA/GATOR version. This sequential number was defined when source records from final data processing were loaded into the Point Source Working Database. Pts_key is incremented in order (or reverse order depending on the scan direction) of declination within a scan. For this reason, on average sources with close pts_key values are close to each other on the sky, except at Tile boundaries. Pts_key ordering thus provides a useful mapping of the 2MASS databases on storage media. Point Source WDB sources are cross-referenced in the Extended Source WDB, Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List via the value of pts_key.
Note: pts_key/cntr values in the Cal-PSWDB are not related to pts_key/cntr in the All-Sky Release Catalogs, Survey Reject Tables, or 6x Working Databases/Catalogs.

hemis %1s --- no Hemisphere code for the 2MASS Observatory from which this source was observed.

"n" = North/Mt. Hopkins

"s" = South/CTIO

date %10s yyyy-mm-dd no The observation reference date for this source expressed in ISO standard format. This is the UT day value at sunrise for the night on which the source was observed. Because it is possible for the UT day to change during a night of observations, the actual UT date for a source measurement can differ from date by one day. Use the Julian Day value (jdate) for a more accurate determination of the observation time of the source.

scan %3d --- no The nightly scan number in which the source was detected.

glon %7.3f deg no Galactic longitude. Galactic coordinate for 2MASS source derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into l_II, b_II coordinate system. This coordinate should not be used as an astrometric reference because it has been rounded to 0.001 deg.

glat %7.3f deg no Galactic latitude. Galactic coordinate for 2MASS source derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into l_II, b_II coordinate system. This coordinate should not be used as an astrometric reference because it has been rounded to 0.001 deg.

x_scan %6.1f arcsec no Mean cross-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance a source lies west or east of the focal plane centerline. Positive values of x_scan indicate that the source falls west of the centerline and negative values indicate the source is east of the centerline. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky. The x_scan value is useful for identifying sources that may be caused or affected by hot pixel events.

y_scan %6.1f arcsec no Mean in-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance an extraction lies north of the edge of a scan from which observations were started. Positive values of y_scan indicate that the scan was north-going and the extraction falls north of the starting edge. Negative values indicate the scan was south-going and the extractions falls south of the starting edge. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky.

jdate %12.4f day no The Julian Date of the source measurement accurate to +30 seconds. This value is extrapolated from the start time of the Calibration scan using the difference between the declinations of the source and the first row in the Tile divided by the scanning rate of the telescope (approximately 5sec). The scanning rate of the two 2MASS telescopes was slightly different because of the need to optimize the dithering of images on the arrays.

Additional Photometric Information

j_psfchi %6.2f --- yes Reduced chi-squared goodness-of-fit value for the J-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have j_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event.
The j_psfchi value is useful as an indicator of photometric quality only if rd_flg[1]="2" for the source, indicating that the default J magnitude (j_m) is from a profile-fitting measurement. A non-null value for j_psfchi may be listed for sources that have rd_flg[1]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in j_m in these cases.
This field is null for rd_flg[1]="0","3","4","6" or "9".

h_psfchi %6.2f --- yes Reduced chi-squared goodness-of-fit value for the H-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have h_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event.
The h_psfchi value is useful as an indicator of photometric quality only if rd_flg[2]="2" for the source, indicating that the default H magnitude (h_m) is from a profile-fitting measurement. A non-null value for h_psfchi may be listed for sources that have rd_flg[2]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in h_m in these cases.
This field is null for rd_flg[2]="0","3","4","6" or "9".

k_psfchi %6.2f --- yes Reduced chi-squared goodness-of-fit value for the K_s-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have k_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event.
The k_psfchi value is useful as an indicator of photometric quality only if rd_flg[3]="2" for the source, indicating that the default J magnitude (k_m) is from a profile-fitting measurement. A non-null value for k_psfchi may be listed for sources that have rd_flg[3]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in k_m in these cases.
This field is null for rd_flg[3]="0","3","4","6" or "9".

j_m_stdap %6.3f mag yes J-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.

j_msig_stdap %5.3f mag yes Uncertainty in the J-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.

h_m_stdap %6.3f mag yes H-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.

h_msig_stdap %5.3f mag yes Uncertainty in the H-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.

k_m_stdap %6.3f mag yes K_s-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.

k_msig_stdap %5.3f mag yes Uncertainty in the K_s-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.

j_m_lgap %6.3f mag yes J-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
If the extraction is not detected in the J-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.

j_msig_lgap %5.3f mag yes Uncertainty in the J-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.

h_m_lgap %6.3f mag yes H-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
If the extraction is not detected in the H-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.

h_msig_lgap %5.3f mag yes Uncertainty in the H-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.

k_m_lgap %6.3f mag yes K_s-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures.
If the extraction is not detected in the K_s-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images.
This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.

k_msig_lgap %5.3f mag yes Uncertainty in the K_s-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.

j_cal %5.3f mag no J-band photometric calibration offset. This number was added to each of the the instrumental J-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.

h_cal %5.3f mag no H-band photometric calibration offset. This number was added to each of the the instrumental H-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.

k_cal %5.3f mag no K_s-band photometric calibration offset. This number was added to each of the the instrumental K_s-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.

j_skyval %7.2f dn yes Estimated J-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.

h_skyval %7.2f dn yes Estimated H-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.

k_skyval %7.2f dn yes Estimated K_s-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.

Additional Source Quality Information

dist_edge_ns %5d arcsec no The distance from the source to the nearest North or South scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The first character of the dist_edge_flg indicates to which edge the source is closer.

dist_edge_ew %3d arcsec no The distance from the source to the nearest East or West scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The second character of the dist_edge_flg indicates to which edge the source is closer.

dist_edge_flg %2s --- no Two character flag that specifies to which scan edges a source lies closest, and to which edges the dist_edge_ns and dist_edge_ew values refer. The first character encodes the N/S edge: "n" means that dist_edge_ns refers to north scan edge, "s" means that dist_edge_ns refers to the south scan edge. The second character encodes the E/W edge: "e" means that dist_edge_ew refers to the east scan edge, "w" means that dist_edge_ew refers to the west scan edge.

spos %5d ---- yes Number of scans covering the position of this extraction. This is computed during the Cal-WDB merging process, using boundaries of each scan that are great-circle interpolations connecting the 3-band coverage corners. Since actual scans "wiggle" slightly in RA due to telescope motions, the actual number of coverages for extractions near scan edges can differ from spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge.

sdet %5d ---- yes Total number of detections of this extraction in any band in this Cal-WDB table, in all scans covering its position, determined during the Cal-WDB merging processing. It is possible to have sdet > spos for extractions near scan edges because of the approximations used to determine spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge.

gcntr %5d ---- yes Unique identification number of the record Merged Point Source Information table corresponding to the merged "group" containing this extraction. The merged "group" contains the combined position and brightness information for all extractions falling within ~1.5" of each other in the Cal-WDB. In confused cases where this extraction appears in more than one group (gcnf>1), the indicated group is the one to which this extraction lies closest. A null value in this column indicates that the source either that the position of this extraction was observed only once, or it was not included in the source merging process because of low reliability, or proximity to a scan edge.

gcnf %1d ---- yes Merging confusion flag. Single digit flag that indicates whether this extraction was associated with more than one group during the Cal-WDB merging process.

"0,1" - Extraction associated with only one group.

"2,3" - Extraction associated with more than one group. Group indicated in the gcntr column is one whose center lies closest to the position of this extraction.

"null" - Extraction was observed only once, or was not included in the source merging process because of low reliability, or proximity to a scan edge.

Optical Source Association Information

a %1s --- no Catalog identifier of an optical source from the USNO-A2.0 catalog that falls within approximately 5´´ of the 2MASS source position. Calibration scan point source extractions were not associated with the Tycho 2 catalog. The values of this column can be:

"0" = no optical source positionally associated with 2MASS source, or the optical association has dist_opt>5´´

"U" = USNO-A2.0 catalog source positionally associated with 2MASS source

Positional association between the 2MASS Cal-PSWDB source and an optical catalog source does not guarantee an identification. Users should consider the separation between the sources, the number of possible optical matches, and consider proper motion when assessing optical counterparts to 2MASS sources.
Because Cal-PSWDB sources with optical associations 5´´ from the 2MASS position have a="0", searches on this column are not sufficient to find all Cal-PSWDB sources with associations. Searches for sources where dist_opt is not null, or is null are more reliable for finding sources with or without optical associations, respectively, with the caveat in the following paragraph.
The optical association information is unreliable for sources with |dec|>86°, because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has |dec|>86°, a value of a="0" and null values in the other optical association fields, dist_opt, phi_opt, b_m_opt, vr_m_opt, do not necessarily mean that there is not an optical association within 5´´ of the 2MASS position.

dist_opt %3.1f arcsec yes Distance separating 2MASS source position and associated optical source within approximately 5´´. This column is null if there is no associated optical source.

phi_opt %4d deg yes Position angle on the sky of the vector from the the associated optical source to the 2MASS source position, in degrees East of North. This column is null if there is no associated optical source.

b_m_opt %5.2f mag yes Photographic blue magnitude of associated optical source. This column is null if there is no associated optical source.

vr_m_opt %5.2f mag yes Photographic red magnitude of the associated optical source. This column is null if there is no associated optical source.

nopt_mchs %1d --- no The number of USNO-A2.0 optical sources found within a radius of approximately 5´´ of the 2MASS position.
The optical association information is unreliable for sources with |dec|>86° because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has |dec|>86°, a value of nopt_mchs="0" does not necessarily mean that there is not an optical association within ~5´´ of the 2MASS position.

Cross-Index Information

ext_key_1 %7d --- yes Unique identification number of the record in the Cal-XSWDB that corresponds to this point source. The Cal-XSWDB record with this ext_key value will have the pts_key for this source in its pts_key column. This allows easy cross-referencing between the two catalogs.

scan_key %5d ---- no Unique identification number of the record in the Calibration Scan Information Table that corresponds to the calibration scan in which this source was detected.

coadd_key %7d ---- no Unique identification number of the record in the Atlas Image Data Table that corresponds to Image in which the position of this source falls.

coadd %3d ---- no Sequence number of the Atlas Image in which the position of this source falls. The Image sequence number is number of the frame that is nearest the center of the Image.

Column Name	Format	Units	nulls	Description
Primary Positional Information
ra	%10.6f	deg	no	J2000 right ascension with respect to the USNOA-2.0 Catalog. Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy.
dec	%10.6f	deg	no	J2000 declination with respect to the USNOA-2.0 Catalog. Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy.
err_maj	%4.2f	arcsec	no	Semi-major axis length of the one sigma position uncertainty ellipse. A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference.
err_min	%4.2f	arcsec	no	Semi-minor axis length of the one sigma position uncertainty ellipse. A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference.
err_ang	%3d	deg	no	Position angle on the sky of the semi-major axis of the position uncertainty ellipse (East of North)
Primary Photometric Information
j_m	%6.3f	mag	yes	Default J-band magnitude, or if the source is not detected in the J-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the first character of the rd_flg value (rd_flg[1]). This column is null if the source is nominally detected in the J-band, but no useful brightness estimate could be made (rd_flg[1]="9").
j_cmsig	%5.3f	mag	yes	Corrected photometric uncertainty for the default J-band magnitude. If rd_flg[1]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[1]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[1]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If j_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[1]="0" or "6") or if the source is not measurable (rd_flg[1]="9").
j_msigcom	%5.3f	mag	yes	Combined, or total photometric uncertainty for the default J-band magnitude. The combined uncertainty is derived from the following relation: j_msigcom = sqrt(j_cmsig² + j_zperr² + fferr² + [r1normrms²]) where j_cmsig = Corrected J-band photometric uncertainty j_zperr = Nightly photometric zero point uncertainty = 0.011 mag fferr = Flat-fielding residual error = 0.005 mags r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[1]="1") This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band).
j_snr	%10.1f	---	yes	J-band "scan" signal-to-noise ratio. This value is given by the ratio of the J-band flux to the characteristic J-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table j_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band).
h_m	%6.3f	mag	yes	Default H-band magnitude, or if the source is not detected in the H-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the second character of the rd_flg value (rd_flg[2]). This column is null if the source is nominally detected in the H-band, but no useful brightness estimate could be made (rd_flg[2]="9").
h_cmsig	%5.3f	mag	yes	Corrected photometric uncertainty for the default H-band magnitude. If rd_flg[2]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[2]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[2]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If h_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[2]="0" or "6") or if the source is not measurable (rd_flg[2]="9").
h_msigcom	%5.3f	mag	yes	Combined, or total photometric uncertainty for the default H-band magnitude. The combined uncertainty is derived from the following relation: h_msigcom = sqrt(h_cmsig² + h_zperr² + fferr² + [r1normrms²]) where h_cmsig = Corrected H-band photometric uncertainty h_zperr = Nightly photometric zero point uncertainty = 0.007 mag fferr = Flat-fielding residual error = 0.005 mags r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[2]="1") This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band).
h_snr	%10.1f	---	yes	H-band "scan" signal-to-noise ratio. This value is given by the ratio of the H-band flux to the characteristic H-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table h_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band).
k_m	%6.3f	mag	yes	Default K_s-band magnitude, or if the source is not detected in the K_s-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the third character of the rd_flg value (rd_flg[3]). This column is null if the source is nominally detected in the K_s-band, but no useful brightness estimate could be made (rd_flg[3]="9").
k_cmsig	%5.3f	mag	yes	Corrected photometric uncertainty for the default K_s-band magnitude. If rd_flg[3]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[3]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[3]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If k_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[3]="0" or "6") or if the source is not measurable (rd_flg[3]="9").
k_msigcom	%5.3f	mag	yes	Combined, or total photometric uncertainty for the default K_s-band magnitude. The combined uncertainty is derived from the following relation: k_msigcom = sqrt(k_cmsig² + k_zperr² + fferr² + [r1normrms²]) where k_cmsig = Corrected K_s-band photometric uncertainty k_zperr = Nightly photometric zero point uncertainty = 0.007 mag fferr = Flat-fielding residual error = 0.005 mags r1normrms = R1 normalization uncertainty = 0.012 mags (applied only for sources with rd_flg[3]="1") This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the K_s-band).
k_snr	%10.1f	---	yes	K_s-band "scan" signal-to-noise ratio. This value is given by the ratio of the K_s-band flux to the characteristic K_s-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table k_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the K_s-band).
Primary Source Quality Information
rel	%1s	----	no	Reliability flag. Single character flag that is related to the probability that the extraction is a valid detection of a near infrared source on the sky at the time of the observation. "A" - P>90% "B" - 80%<P<90% "C" - 70%<P<80% "D" - 50%<P<70% "E" - 20%<P<50% "F" - P<20% This flag does not provide information about the quality of the position or flux measurement. For that, users should refer to the ph_qual, rd_flg, cc_flg and positional and photometric uncertainties.
ph_qual	%3s	---	no	Photometric quality flag. Three character flag, one character per band [JHK_s], that provides a summary of the net quality of the default photometry in each band, as derived from the Read Flag (rd_flg), measurement uncertainties ([jhk]_cmsig), scan signal-to-noise ratios ([jhk]_snr), frame-detection statistics (ndet), and profile-fit reduced chi-squared values ([jhk]_psfchi). The value for ph_qual is set for a band according to the precedence of the table below. For example, a source that is tested and meets the conditions for category "X" is not tested for subsequent qualities. "X" - There is a detection at this location, but no valid brightness estimate can be extracted using any algorithm. rd_flg="9" and default magnitude is null. "U" - Upper limit on magnitude. Source is not detected in this band (rd_flg="0"), or it is detected, but not resolved in a consistent fashion with other bands (rd_flg="6"). A value of ph_qual="U" does not necessarily mean that there is no flux detected in this band at the location. Whether or not flux has been detected can be determined from the value of rd_flg. When rd_flg="0", no flux has been detected. When rd_flg="6", flux has been detected at the location where the images were not deblended consistently in all three bands (JHK_s). "Z" - The detection in this band is positionally associated with the predicted location of an image artifact. The cc_flg value in this band will be C,D,G or P. "F" - This category includes rd_flg="1" or rd_flg="3" sources where a reliable estimate of the photometric error, [jhk]_cmsig, could not be determined. The uncertainties reported for these sources in [jhk]_cmsig and [jhk]_msigcom are flags and have numeric values >8.0. "E" - This category includes detections where the goodness-of-fit quality of the profile-fit photometry was very poor (rd_flg="2" and [jhk]psf_chi>10.0), or detections where psf fit photometry did not converge and an aperture magnitude is reported (rd_flg="4"), or detections where the number of frames was too small in relation to the number of frames in which a detection was geometrically possible (rd_flg="1" or rd_flg="2"). "A" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>10 AND [jhk]_cmsig<0.10857. "B" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>7 AND [jhk]_cmsig<0.15510. "C" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with [jhk]_snr>5 AND [jhk]_cmsig<0.21714. "D" - Detections in any brightness regime where valid measurements were made (rd_flg="1","2" or "3") with no [jhk]_snr or [jhk]_cmsig requirement.
rd_flg	%3s	---	no	Read flag. Three character flag, one character per band [JHK_s], that indicates the origin of the default magnitudes and uncertainties in each band (j_m,h_m,k_m, j_cmsig, h_cmsig, k_cmsig). Rd_flg values of "1", "2" or "3" generally indicate the best quality detections, photometry and astrometry (although other quality flags must be considered). Values of "0", "4", "6" and "9" in a band indicate either non-detections, or generally poor quality photometry and positions. The definitions of the rd_flg values are: "0" - Source is not detected in this band. The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". "1" - The default magnitude is derived from aperture photometry measurements on the 51 ms "Read_1" exposures. The aperture radius is 4", with the sky background measured in an annulus with an inner radius of 14" and an outer radius of 20". Used for sources that saturate one or more of the 1.3s "Read_2" exposures, but are not saturated on at least one of the 51 ms "Read_1" frames. "2" - The default magnitude is derived from a profile-fitting measurement made on the 1.3 sec "Read_2" exposures. The profile-fit magnitudes are normalized to curve-of-growth-corrected aperture magnitudes. This is the most common type in the Cal-PSWDBs, and is used for sources that have no saturated pixels in any of the 1.3 sec exposures. "3" - The default magnitude is derived from a 1-d radial profile fitting measurement made on the 51 ms "Read_1" exposures. Used for very bright sources that saturate all of the 51 ms "Read 1" exposures. "4" - The default magnitude is derived from curve-of-growth-corrected 4" radius aperture photometry measurements on the 1.3 s "Read_2" exposures. This is used for sources that are not saturated in any of the Read_2 frames, but where the profile-fitting measurements fail to converge to a solution. These magnitudes are the same as the standard aperture magnitudes (j_m_stdap, h_m_stdap, k_m_stdap), but when they are the default magnitudes, it generally implies that they are low quality measurements. "6" - The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for pairs of sources which are detected and resolved in another band, but are detected and not resolved in this band. This differs from a rd_flg="0" because in this case there is a detection of the source in this band, but it is not consistently resolved across all bands. "9" - The default magnitude is the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The sky background is estimated in an annular region with inner radius of 14" and outer radius of 20". This is used for sources that were nominally detected in this band, but which could not have a useful brightness measurement from either profile fitting or aperture photometry. This often occurs in highly confused regions, or very near Tile edges where a significant fraction of the measurement aperture of sky annulus falls off the focal plane.
bl_flg	%3s	---	no	Blend flag. Three character flag, one character per band [JHK_s], that indicates the number of components that were fit simultaneously when estimating the brightness of a source: "0" - Source is not detected, or is inconsistently deblended in that band. "1" - One component was fit to the source in R_2 profile-fitting photometry (rd_flg="2"), or default magnitudes are from aperture photometry (rd_flg="1" or "4") or saturated star 1-d radial profile-fitting (rd_flg="3"). ">1" - More than one component was fit simultaneously during R2 profile-fit photometry, where the value of the field is the number of components simultaneously fit. The maximum number of components is 7 in any band for the Cal-PSWDBs, so this bl_flg is always a three character flag. Multi-component fitting occurs only for profile-fitting, and only when more than one detection is found within ~5". Single detections that are not well-fit by a single PSF are not split.
cc_flg	%3s	---	no	Contamination and confusion flag. Three character flag, one character per band [JHK_s], that indicates that the extraction is associated with the predicted position of an image artifact, or that the photometry and/or position measurements of a source may be contaminated or biased due to proximity to an image artifact or nearby source of equal or greater brightness. The cc_flg in each band is set in hierarchical order according to the following table, in the event a source is affected by more than one artifact or condition: "P" = Persistence artifact. Extraction is likely a spurious detection of a latent image left by a nearby bright star. "G" = Dichroic glint artifact. Extraction is likely a spurious detection of a dichroic glint produced by a nearby bright star. "C" = Confusion artifact. Extraction is likely a spurious detection in the wings of a nearby bright star. "D" = Diffraction spike artifact. Extraction is likely a spurious detection on a diffraction spike from a nearby star. "p" = Persistence. Source may be contaminated by a latent image left by a nearby bright star. "c" = Photometric Confusion. Source photometry is biased by a nearby star that has contaminated the background estimation. This is very common in high source density regions. "d" = Diffraction spike confusion. Source may be contaminated by a diffraction spike from a nearby star. "s" = Electronic stripe. Source measurement may be contaminated by a stripe from a nearby bright star. "b" = Bandmerge confusion. In the process of merging detections in the different bands for this source, there was more than one possible match between the different band components. This occurs in regions of very high source density, or when multiple sources were split in one band but not another. "0" = Source is unaffected by known artifacts, or is not detected in the band. Non-zero values the cc_flg in any band is an indicator that the extraction may be a spurious detection of an image artifact, or that measurements of that source may be contaminated.
ndet	%6s	---	no	Frame detection statistics. A six-character flag, two characters per band [JJHHK_sK_s], that indicates the number frames on which a source was detected, N, and the number of frames on which the source could have been measured, M. The first digit in the pair for each band, N, gives the number of frames on which there were >3 sigma aperture photometry detections of the source. The second digit for each band, M, gives the number of frames on which aperture measurements were possible. Normally, M=6, (occasionally M=7 because the scanning step size was slightly less than 1/6 of the frame size). M can be <6 if frames are "lost" because: a) there were masked pixels within the source aperture due to cosmic ray detections, noisy pixels, meteor trails, etc, or b) there were saturated pixels within the source aperture. Values of M < 6 are not uncommon, but do indicate an effective loss of coverage and sensitivity for a source. The values of N and M for a band always pertain to the aperture photometry on the 51 ms "Read_1" exposures if rd_flg="1", and to the aperture photometry on the 1.3 s "Read_2" exposures if rd_flg="2" or "4". Sources that are saturated on all of the Read_1 frames (rd_flg="3") have N=0 because no aperture photometry was possible. Sources with signal-to-noise ratios >8-9 should be detected on all available frames. Values of N < M for such sources are an indication of possible loss of measurement integrity. Values of N < M, or even N=0, are normal for fainter sources because they are too faint on individual frames to yield a >3 sigma detection.
gal_contam	%1d	---	no	Extended source "contamination" flag. A value of gal_contam="2" indicates that this point source falls within the elliptical boundary of an All-Sky XSC source defined by the semi-major axis and ellipticity of the 20 mag arcsec^-2 K_s-band elliptical isophote (r_k20fe) +10%, for XSC sources where r_k20fe is >10''. Sources so indicated are often foreground stars superimposed on background galaxies, or sometimes extractions of pieces of the galaxy or nebula. The point source photometry for these sources is probably contaminated by the surrounding structured extended emission. Point sources can still be superimposed on extended sources and remain unflagged if the XSC source shape is not well-described by an ellipse. This flag also denotes (gal_contam="1") Cal-PSWDB sources that are equivalent to sources in the XSC, usually the nuclei of galaxies. The Cal-PSWDB gal_contam values correctly flag all point sources that are found to be resolved relative to a single point-spread-function, regardless of extended source size. The gal_contam="1" flagging in the Cal-PSWDB is correct only for XSC sources with r_k20fe >10'' (I.6.b.xii). "0" - Source does not fall within the elliptical profile of an extended source with semi-major axis >10'', or it is not identified exactly with an Cal-XSWDB source with semi-major axis >10''. However, the source may correspond exactly to a smaller XSC source. "1" - Source is resolved by 2MASS, and is equivalent to a source in the Cal-XSWDB that has a semi-major axis >10'' in size. "2" - Source falls within the elliptical boundary of an XSC source that has a semi-major axis >10'' in size.
mp_flg	%1d	---	no	Minor Planet Flag. Indicates if this source is associated with the predicted position of a known minor planet, comet, planet or planetary satellite. This association does not guarantee that the Cal-PSWDB source is a detection of the solar system object. "0" - Source is not associated with a known solar system object "1" - Source is associated with the predicted position of a known solar system object. The name and orbital data for the associated objects are given in the Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List. The associated Cal-PSWDB source is cross-referenced in those Lists via the value of pts_key
Additional Positional and Identification Information
pts_key/cntr	%10d	---	no	A unique identification number for the Working Database entry. This column is called pts_key in the DVD-ROM and ftp versions of the Working Databases and cntr in the IRSA/GATOR version. This sequential number was defined when source records from final data processing were loaded into the Point Source Working Database. Pts_key is incremented in order (or reverse order depending on the scan direction) of declination within a scan. For this reason, on average sources with close pts_key values are close to each other on the sky, except at Tile boundaries. Pts_key ordering thus provides a useful mapping of the 2MASS databases on storage media. Point Source WDB sources are cross-referenced in the Extended Source WDB, Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List via the value of pts_key. Note: pts_key/cntr values in the Cal-PSWDB are not related to pts_key/cntr in the All-Sky Release Catalogs, Survey Reject Tables, or 6x Working Databases/Catalogs.
hemis	%1s	---	no	Hemisphere code for the 2MASS Observatory from which this source was observed. "n" = North/Mt. Hopkins "s" = South/CTIO
date	%10s	yyyy-mm-dd	no	The observation reference date for this source expressed in ISO standard format. This is the UT day value at sunrise for the night on which the source was observed. Because it is possible for the UT day to change during a night of observations, the actual UT date for a source measurement can differ from date by one day. Use the Julian Day value (jdate) for a more accurate determination of the observation time of the source.
scan	%3d	---	no	The nightly scan number in which the source was detected.
glon	%7.3f	deg	no	Galactic longitude. Galactic coordinate for 2MASS source derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into l_II, b_II coordinate system. This coordinate should not be used as an astrometric reference because it has been rounded to 0.001 deg.
glat	%7.3f	deg	no	Galactic latitude. Galactic coordinate for 2MASS source derived by precessing reconstructed ra and dec to B1950, and performing rotational transformation into l_II, b_II coordinate system. This coordinate should not be used as an astrometric reference because it has been rounded to 0.001 deg.
x_scan	%6.1f	arcsec	no	Mean cross-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance a source lies west or east of the focal plane centerline. Positive values of x_scan indicate that the source falls west of the centerline and negative values indicate the source is east of the centerline. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky. The x_scan value is useful for identifying sources that may be caused or affected by hot pixel events.
y_scan	%6.1f	arcsec	no	Mean in-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance an extraction lies north of the edge of a scan from which observations were started. Positive values of y_scan indicate that the scan was north-going and the extraction falls north of the starting edge. Negative values indicate the scan was south-going and the extractions falls south of the starting edge. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky.
jdate	%12.4f	day	no	The Julian Date of the source measurement accurate to +30 seconds. This value is extrapolated from the start time of the Calibration scan using the difference between the declinations of the source and the first row in the Tile divided by the scanning rate of the telescope (approximately 5sec). The scanning rate of the two 2MASS telescopes was slightly different because of the need to optimize the dithering of images on the arrays.
Additional Photometric Information
j_psfchi	%6.2f	---	yes	Reduced chi-squared goodness-of-fit value for the J-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have j_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event. The j_psfchi value is useful as an indicator of photometric quality only if rd_flg[1]="2" for the source, indicating that the default J magnitude (j_m) is from a profile-fitting measurement. A non-null value for j_psfchi may be listed for sources that have rd_flg[1]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in j_m in these cases. This field is null for rd_flg[1]="0","3","4","6" or "9".
h_psfchi	%6.2f	---	yes	Reduced chi-squared goodness-of-fit value for the H-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have h_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event. The h_psfchi value is useful as an indicator of photometric quality only if rd_flg[2]="2" for the source, indicating that the default H magnitude (h_m) is from a profile-fitting measurement. A non-null value for h_psfchi may be listed for sources that have rd_flg[2]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in h_m in these cases. This field is null for rd_flg[2]="0","3","4","6" or "9".
k_psfchi	%6.2f	---	yes	Reduced chi-squared goodness-of-fit value for the K_s-band profile-fit photometry made on the 1.3 s "Read_2" exposures. Unresolved sources that are well-fit by a single PSF should have k_psfchi~1.0. Values >2 indicate that the source was not well-fit by a single PSF and that the profile-fitting measurement may not accurately capture the flux of the object. This can occur if the source is resolved, part of a multiple star group, or is corrupted by a cosmic ray or hot pixel event. The k_psfchi value is useful as an indicator of photometric quality only if rd_flg[3]="2" for the source, indicating that the default J magnitude (k_m) is from a profile-fitting measurement. A non-null value for k_psfchi may be listed for sources that have rd_flg[3]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in k_m in these cases. This field is null for rd_flg[3]="0","3","4","6" or "9".
j_m_stdap	%6.3f	mag	yes	J-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.
j_msig_stdap	%5.3f	mag	yes	Uncertainty in the J-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.
h_m_stdap	%6.3f	mag	yes	H-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.
h_msig_stdap	%5.3f	mag	yes	Uncertainty in the H-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.
k_m_stdap	%6.3f	mag	yes	K_s-band "standard" aperture magnitude. This is the curve-of-growth corrected average brightness measured in a 4" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. The curve-of-growth correction adjusts to an "infinite" aperture using a normalization value derived from a series of multi-aperture measurements made from many stars having the same seeing FWHM as the source that is corrected. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.
k_msig_stdap	%5.3f	mag	yes	Uncertainty in the K_s-band standard aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.
j_m_lgap	%6.3f	mag	yes	J-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the J-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.
j_msig_lgap	%5.3f	mag	yes	Uncertainty in the J-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures.
h_m_lgap	%6.3f	mag	yes	H-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the H-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.
h_msig_lgap	%5.3f	mag	yes	Uncertainty in the H-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures.
k_m_lgap	%6.3f	mag	yes	K_s-band large aperture magnitude. This is the average brightness measured in a 10" radius aperture centered on the source position on each of the available 1.3 s "Read_2" frames. The background sky reference on each frame is measured in an annular region with inner radius of 14" and outer radius of 20". Non-detections on individual frames are included in the average so that the flux is not statistically overestimated. No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the K_s-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.
k_msig_lgap	%5.3f	mag	yes	Uncertainty in the K_s-band large aperture magnitude. If there was more than one 1.3 s "Read_2" frame available for aperture photometry, this the RMS residual of the brightness measured on the individual frames. If there was only one frame available, this is the uncertainty derived from the single measurement using the poisson statistics of the fluxes in the aperture and sky annulus. This column is null if the source is not detected in the K_s-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" K_s-band exposures.
j_cal	%5.3f	mag	no	J-band photometric calibration offset. This number was added to each of the the instrumental J-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.
h_cal	%5.3f	mag	no	H-band photometric calibration offset. This number was added to each of the the instrumental H-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.
k_cal	%5.3f	mag	no	K_s-band photometric calibration offset. This number was added to each of the the instrumental K_s-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms.
j_skyval	%7.2f	dn	yes	Estimated J-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.
h_skyval	%7.2f	dn	yes	Estimated H-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.
k_skyval	%7.2f	dn	yes	Estimated K_s-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images.
Additional Source Quality Information
dist_edge_ns	%5d	arcsec	no	The distance from the source to the nearest North or South scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The first character of the dist_edge_flg indicates to which edge the source is closer.
dist_edge_ew	%3d	arcsec	no	The distance from the source to the nearest East or West scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The second character of the dist_edge_flg indicates to which edge the source is closer.
dist_edge_flg	%2s	---	no	Two character flag that specifies to which scan edges a source lies closest, and to which edges the dist_edge_ns and dist_edge_ew values refer. The first character encodes the N/S edge: "n" means that dist_edge_ns refers to north scan edge, "s" means that dist_edge_ns refers to the south scan edge. The second character encodes the E/W edge: "e" means that dist_edge_ew refers to the east scan edge, "w" means that dist_edge_ew refers to the west scan edge.
spos	%5d	----	yes	Number of scans covering the position of this extraction. This is computed during the Cal-WDB merging process, using boundaries of each scan that are great-circle interpolations connecting the 3-band coverage corners. Since actual scans "wiggle" slightly in RA due to telescope motions, the actual number of coverages for extractions near scan edges can differ from spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge.
sdet	%5d	----	yes	Total number of detections of this extraction in any band in this Cal-WDB table, in all scans covering its position, determined during the Cal-WDB merging processing. It is possible to have sdet > spos for extractions near scan edges because of the approximations used to determine spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge.
gcntr	%5d	----	yes	Unique identification number of the record Merged Point Source Information table corresponding to the merged "group" containing this extraction. The merged "group" contains the combined position and brightness information for all extractions falling within ~1.5" of each other in the Cal-WDB. In confused cases where this extraction appears in more than one group (gcnf>1), the indicated group is the one to which this extraction lies closest. A null value in this column indicates that the source either that the position of this extraction was observed only once, or it was not included in the source merging process because of low reliability, or proximity to a scan edge.
gcnf	%1d	----	yes	Merging confusion flag. Single digit flag that indicates whether this extraction was associated with more than one group during the Cal-WDB merging process. "0,1" - Extraction associated with only one group. "2,3" - Extraction associated with more than one group. Group indicated in the gcntr column is one whose center lies closest to the position of this extraction. "null" - Extraction was observed only once, or was not included in the source merging process because of low reliability, or proximity to a scan edge.
Optical Source Association Information
a	%1s	---	no	Catalog identifier of an optical source from the USNO-A2.0 catalog that falls within approximately 5´´ of the 2MASS source position. Calibration scan point source extractions were not associated with the Tycho 2 catalog. The values of this column can be: "0" = no optical source positionally associated with 2MASS source, or the optical association has dist_opt>5´´ "U" = USNO-A2.0 catalog source positionally associated with 2MASS source Positional association between the 2MASS Cal-PSWDB source and an optical catalog source does not guarantee an identification. Users should consider the separation between the sources, the number of possible optical matches, and consider proper motion when assessing optical counterparts to 2MASS sources. Because Cal-PSWDB sources with optical associations 5´´ from the 2MASS position have a="0", searches on this column are not sufficient to find all Cal-PSWDB sources with associations. Searches for sources where dist_opt is not null, or is null are more reliable for finding sources with or without optical associations, respectively, with the caveat in the following paragraph. The optical association information is unreliable for sources with \|dec\|>86°, because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has \|dec\|>86°, a value of a="0" and null values in the other optical association fields, dist_opt, phi_opt, b_m_opt, vr_m_opt, do not necessarily mean that there is not an optical association within 5´´ of the 2MASS position.
dist_opt	%3.1f	arcsec	yes	Distance separating 2MASS source position and associated optical source within approximately 5´´. This column is null if there is no associated optical source.
phi_opt	%4d	deg	yes	Position angle on the sky of the vector from the the associated optical source to the 2MASS source position, in degrees East of North. This column is null if there is no associated optical source.
b_m_opt	%5.2f	mag	yes	Photographic blue magnitude of associated optical source. This column is null if there is no associated optical source.
vr_m_opt	%5.2f	mag	yes	Photographic red magnitude of the associated optical source. This column is null if there is no associated optical source.
nopt_mchs	%1d	---	no	The number of USNO-A2.0 optical sources found within a radius of approximately 5´´ of the 2MASS position. The optical association information is unreliable for sources with \|dec\|>86° because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has \|dec\|>86°, a value of nopt_mchs="0" does not necessarily mean that there is not an optical association within ~5´´ of the 2MASS position.
Cross-Index Information
ext_key_1	%7d	---	yes	Unique identification number of the record in the Cal-XSWDB that corresponds to this point source. The Cal-XSWDB record with this ext_key value will have the pts_key for this source in its pts_key column. This allows easy cross-referencing between the two catalogs.
scan_key	%5d	----	no	Unique identification number of the record in the Calibration Scan Information Table that corresponds to the calibration scan in which this source was detected.
coadd_key	%7d	----	no	Unique identification number of the record in the Atlas Image Data Table that corresponds to Image in which the position of this source falls.
coadd	%3d	----	no	Sequence number of the Atlas Image in which the position of this source falls. The Image sequence number is number of the frame that is nearest the center of the Image.

[Last Updated: 2008 February 18, by R. Cutri]

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