II. User's Guide to the 2MASS All-Sky Data Release

2. Point Source Catalog (PSC)

a. Column Descriptions

The following table contains brief descriptions of the parameters provided for each source in the 2MASS All Sky Release PSC. The table is organized according to the broad function and utility of the parameters: positional information, photometric information, and source quality information. For PSC flag parameters, the meaning of each possible flag value is given, along with some practical information on their usage.

The columns in the following table are:

Column Name: The parameter name in the PSC 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 PSC, 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 PSC tables drawn from either IRSA/GATOR output or the ascii DVD-ROM or ftp versions.

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

nulls: A "yes" in this column means that this parameter can be null in the PSC. A "no" means that there will always be a value in this column in the PSC. Note that null values are represented differently in the IRSA/GATOR output and the ascii DVD-ROM or ftp versions of the PSC.

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 ICRS

dec %10.6f deg no J2000 declination with respect to the ICRS

err_maj %4.2f arcsec no Semi-major axis length of the one sigma position uncertainty ellipse

err_min %4.2f arcsec no Semi-minor axis length of the one sigma position uncertainty ellipse

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

designation %17s --- no Sexagesimal, equatorial position-based source name in the form: hhmmssss+ddmmsss[ABC...]. The full naming convention for 2MASS All-Sky Release PSC sources has the form "2MASS Jhhmmssss+ddmmsss[ABC...]", where "2MASS" indicates that the source is from the All-Sky PSC, "J" indicates the position is J2000, and the optional trailing letters are used to distinguish sources with otherwise duplicate names. The "2MASS J" prefix is not listed explicitly in the designation column.
CAUTION: Coordinates extracted from the designation column are less accurate than those given in the right ascension and declination columns of the Catalogs. The use of designation coordinates will result in a maximum (unsigned) error of 0.0996" in declination and a maximum (unsigned degree) error of 0.1488" in right ascension.

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 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 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 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
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).

"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 PSC, 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 PSC, 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 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. 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 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.

prox %5.1f arcsec no Proximity. The distance between this source and its nearest neighbor in the PSC. The pts_key of the nearest source is given in the pxcntr column. The effective resolution of the 2MASS system is approximately 5". Any source with prox < 6" is potentially confused with a nearby object, and should be used with caution.

pxpa %3d deg yes The position angle on the sky of the vector from the source to the nearest neighbor in the PSC, in degrees East of North. This column in null if prox=0.0, which occurs only for confused sources or from errors in the bandmerge process caused by confusion.

pxcntr %10d --- no The pts_key value of the nearest source in the PSC.

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 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") PSC sources that are equivalent to sources in the XSC, but only for XSC sources with r_k20fe is >10''. Since most XSC sources have semi-major axes <10'', gal_contam does not identify all PSC sources with exact XSC counterparts. Use the ext_key to identify all PSC sources that were found to be resolved relative to a single point-spread function..

"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 XSC 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 XSC that has a semi-major axis >10'' in size. Users must refer to the ext_key to identify all PSC sources with XSC counterparts.
"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 PSC 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 PSC 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 PSC source. This column is called pts_key in the DVD-ROM and ftp versions of the PSC 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 release on storage media. PSC sources are cross-referenced in the XSC, Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List via the value of pts_key.

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.

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 Survey 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. The amplitude of the correction is tabulated in the j_ap_cor value in the Atlas Image Information Table.
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. The amplitude of the correction is tabulated in the h_ap_cor value in the Atlas Image Information Table.
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. The amplitude of the correction is tabulated in the k_ap_cor value in the Atlas Image Information Table.
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.

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 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 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.

dup_src %1d --- no Duplicate source flag. Used in conjunction with the use_src flag, this numerical flag indicates whether the source falls in a Tile overlap region, and if so, if it was detected multiple times.

"0" = The source does not fall within a Tile overlap region (use_src="1"), or it falls in an overlap region and there were no sources detected within 2" of its position in the overlapping Tile (use_src="0").

"1" = The source falls within a Tile overlap region, and there is one source detected within 2" of its position in the overlapping Tile.

">1" = The source falls within a Tile overlap region, and there are multiple sources detected within 2" of its position in the overlapping Tile, and/or within its own Tile. This implies confusion in the multiple source resolution procedure.

use_src %1d --- no Use source flag. Used in conjunction with the dup_src flag, this numerical flag indicates if a source falls within a Tile overlap region, and whether or not it satisfies the unbiased selection rules for multiple source resolution.

"1" = The source does not fall in a Tile overlap region (dup_src="0"), or it falls in an overlap region, but lies farther from its scan edge than any apparition of the source in another Tile. A source must have use_src="1" to be considered part of the sub-Catalog that satisfies the 2MASS Level 1 Science Requirements

"0" = The source falls in a Tile overlap region, but does not have a detection within 2" of its position in any overlapping Tiles. PSC sources with use_src="0" will always have dup_src="0". Such objects are usually faint, and thus toggling above and below the detection limits, or may have moved between the scans of the different Tiles.

Optical Source Association Information

a %1s --- no Catalog identifier of an optical source from either the Tycho 2 or USNO-A2.0 catalog that falls within approximately 5´´ of the 2MASS source position. An association with Tycho 2 takes precedence over USNO-A2.0. The values of this column can be:

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

"T" = Tycho 2 catalog source positionally associated with 2MASS source

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

Positional association between the 2MASS PSC 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 PSC sources with optical associations 5´´ from the 2MASS position have a="0", searches on this column are not sufficient to find all PSC 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´´. For Tycho 2 associations (a="T"), the separation is computed for the position of the Tycho 2 source corrected for proper motion to the time of the 2MASS observation (if proper motions are provided in Tycho 2). 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 is opposite to the sense of prox which is the vector from the 2MASS source position to the nearest neighbor in the PSC. This column is null if there is no associated optical source.

b_m_opt %5.2f mag yes Blue magnitude of associated optical source. If Tycho 2 (a="T"), then this is the Johnson B magnitude (B_J, derived from B_Tycho and V_Tycho using the transformations given in Høg (2000): B_J-V_J = 0.85*(B_T-V_T). If USNO-A2.0 (a="U"), then this is the photographic blue magnitude. This column is null if there is no associated optical source.

vr_m_opt %5.2f mag yes Visual or red magnitude of the associated optical source. If Tycho 2 (a="T"), then this is the Johnson V magnitude (V_J), derived from B_Tycho and V_Tycho using the transformations given in Høg (2000): V_J = V_T - 0.09*(B_T-V_T). If USNO-A2.0 (a="U"), then this is the photographic red magnitude. This column is null if there is no associated optical source.

nopt_mchs %1d --- no The number of USNO-A2.0 or Tycho 2 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 %7d --- yes Unique identification number of the record in the XSC that corresponds to this point source. The XSC 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 Scan Information Table that corresponds to the survey scan in which this source was detected.

coadd_key %7d ---- no Unique identification number of the record in the Atlas Image Information 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 ICRS
dec	%10.6f	deg	no	J2000 declination with respect to the ICRS
err_maj	%4.2f	arcsec	no	Semi-major axis length of the one sigma position uncertainty ellipse
err_min	%4.2f	arcsec	no	Semi-minor axis length of the one sigma position uncertainty ellipse
err_ang	%3d	deg	no	Position angle on the sky of the semi-major axis of the position uncertainty ellipse (East of North)
designation	%17s	---	no	Sexagesimal, equatorial position-based source name in the form: hhmmssss+ddmmsss[ABC...]. The full naming convention for 2MASS All-Sky Release PSC sources has the form "2MASS Jhhmmssss+ddmmsss[ABC...]", where "2MASS" indicates that the source is from the All-Sky PSC, "J" indicates the position is J2000, and the optional trailing letters are used to distinguish sources with otherwise duplicate names. The "2MASS J" prefix is not listed explicitly in the designation column. CAUTION: Coordinates extracted from the designation column are less accurate than those given in the right ascension and declination columns of the Catalogs. The use of designation coordinates will result in a maximum (unsigned) error of 0.0996" in declination and a maximum (unsigned degree) error of 0.1488" in right ascension.
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 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 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 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
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). "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 PSC, 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 PSC, 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 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. 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 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.
prox	%5.1f	arcsec	no	Proximity. The distance between this source and its nearest neighbor in the PSC. The pts_key of the nearest source is given in the pxcntr column. The effective resolution of the 2MASS system is approximately 5". Any source with prox < 6" is potentially confused with a nearby object, and should be used with caution.
pxpa	%3d	deg	yes	The position angle on the sky of the vector from the source to the nearest neighbor in the PSC, in degrees East of North. This column in null if prox=0.0, which occurs only for confused sources or from errors in the bandmerge process caused by confusion.
pxcntr	%10d	---	no	The pts_key value of the nearest source in the PSC.
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 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") PSC sources that are equivalent to sources in the XSC, but only for XSC sources with r_k20fe is >10''. Since most XSC sources have semi-major axes <10'', gal_contam does not identify all PSC sources with exact XSC counterparts. Use the ext_key to identify all PSC sources that were found to be resolved relative to a single point-spread function.. "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 XSC 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 XSC that has a semi-major axis >10'' in size. Users must refer to the ext_key to identify all PSC sources with XSC counterparts. "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 PSC 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 PSC 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 PSC source. This column is called pts_key in the DVD-ROM and ftp versions of the PSC 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 release on storage media. PSC sources are cross-referenced in the XSC, Known Asteroid Detection List, Known Comet Detection List, and Planet and Planetary Satellite Detection List via the value of pts_key.
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.
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 Survey 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. The amplitude of the correction is tabulated in the j_ap_cor value in the Atlas Image Information Table. 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. The amplitude of the correction is tabulated in the h_ap_cor value in the Atlas Image Information Table. 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. The amplitude of the correction is tabulated in the k_ap_cor value in the Atlas Image Information Table. 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.
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 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 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.
dup_src	%1d	---	no	Duplicate source flag. Used in conjunction with the use_src flag, this numerical flag indicates whether the source falls in a Tile overlap region, and if so, if it was detected multiple times. "0" = The source does not fall within a Tile overlap region (use_src="1"), or it falls in an overlap region and there were no sources detected within 2" of its position in the overlapping Tile (use_src="0"). "1" = The source falls within a Tile overlap region, and there is one source detected within 2" of its position in the overlapping Tile. ">1" = The source falls within a Tile overlap region, and there are multiple sources detected within 2" of its position in the overlapping Tile, and/or within its own Tile. This implies confusion in the multiple source resolution procedure.
use_src	%1d	---	no	Use source flag. Used in conjunction with the dup_src flag, this numerical flag indicates if a source falls within a Tile overlap region, and whether or not it satisfies the unbiased selection rules for multiple source resolution. "1" = The source does not fall in a Tile overlap region (dup_src="0"), or it falls in an overlap region, but lies farther from its scan edge than any apparition of the source in another Tile. A source must have use_src="1" to be considered part of the sub-Catalog that satisfies the 2MASS Level 1 Science Requirements "0" = The source falls in a Tile overlap region, but does not have a detection within 2" of its position in any overlapping Tiles. PSC sources with use_src="0" will always have dup_src="0". Such objects are usually faint, and thus toggling above and below the detection limits, or may have moved between the scans of the different Tiles.
Optical Source Association Information
a	%1s	---	no	Catalog identifier of an optical source from either the Tycho 2 or USNO-A2.0 catalog that falls within approximately 5´´ of the 2MASS source position. An association with Tycho 2 takes precedence over USNO-A2.0. The values of this column can be: "0" = no optical source positionally associated with 2MASS source, or the optical association has dist_opt>5´´ "T" = Tycho 2 catalog source positionally associated with 2MASS source "U" = USNO-A2.0 catalog source positionally associated with 2MASS source Positional association between the 2MASS PSC 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 PSC sources with optical associations 5´´ from the 2MASS position have a="0", searches on this column are not sufficient to find all PSC 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´´. For Tycho 2 associations (a="T"), the separation is computed for the position of the Tycho 2 source corrected for proper motion to the time of the 2MASS observation (if proper motions are provided in Tycho 2). 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 is opposite to the sense of prox which is the vector from the 2MASS source position to the nearest neighbor in the PSC. This column is null if there is no associated optical source.
b_m_opt	%5.2f	mag	yes	Blue magnitude of associated optical source. If Tycho 2 (a="T"), then this is the Johnson B magnitude (B_J, derived from B_Tycho and V_Tycho using the transformations given in Høg (2000): B_J-V_J = 0.85(B_T-V_T). If USNO-A2.0 (a="U"), then this is the photographic blue magnitude. This column is null* if there is no associated optical source.
vr_m_opt	%5.2f	mag	yes	Visual or red magnitude of the associated optical source. If Tycho 2 (a="T"), then this is the Johnson V magnitude (V_J), derived from B_Tycho and V_Tycho using the transformations given in Høg (2000): V_J = V_T - 0.09(B_T-V_T). If USNO-A2.0 (a="U"), then this is the photographic red magnitude. This column is null* if there is no associated optical source.
nopt_mchs	%1d	---	no	The number of USNO-A2.0 or Tycho 2 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	%7d	---	yes	Unique identification number of the record in the XSC that corresponds to this point source. The XSC 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 Scan Information Table that corresponds to the survey scan in which this source was detected.
coadd_key	%7d	----	no	Unique identification number of the record in the Atlas Image Information 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: 2006 December 18, by R. Cutri]

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