ACDS V10.0 - Detailed Description of II/246

ACDS V10.0 - Mon Jan 20 10:22:27 CET 2025

| # Detailed Description of II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) |

Note : this is the description file of the original catalog. This HTML page corresponds well to the original description, but some minor changes in the format may have been introduced in the FITS output files in order to allow for arithmetic operations on quantities such as coordinates and times. h:m:s and d:m:s units are normally converted into degrees, and YYYY-MM-DD into julian days.
Similarly, some slight changes may have been introduced in the units; the value given in the HTML files supersedes the value indicated in the ReadMe file for this catalogue.

    II/246              2MASS All-Sky Catalog of Point Sources     (Cutri+ 2003)
    ================================================================================
    The 2MASS All-Sky Catalog of Point Sources
         Cutri R.M., Skrutskie M.F., Van Dyk S., Beichman C.A., Carpenter J.M.,
         Chester T., Cambresy L., Evans T., Fowler J., Gizis J., Howard E.,
         Huchra J., Jarrett T., Kopan E.L., Kirkpatrick J.D., Light R.M,
         Marsh K.A., McCallon H., Schneider S., Stiening R., Sykes M.,
         Weinberg M., Wheaton W.A., Wheelock S., Zacarias N.
        <University of Massachusetts and Infrared Processing and Analysis Center
         (IPAC/California Institute of Technology) (2003)>
        =2003yCat.2246....0C
    ================================================================================
    ADC_Keywords: Infrared sources ; Photometry, infrared ; Surveys

    Description:

        The Two Micron All Sky Survey (2MASS) project is designed to close the
        gap between our current technical capability and our knowledge of the
        near-infrared sky. In addition to providing a context for the
        interpretation of results obtained at infrared and other wavelengths,
        2MASS will provide direct answers to immediate questions on the
        large-scale structure of the Milky Way and the Local Universe.

        To achieve these goals, 2MASS is uniformly scanning the entire sky in
        three near-infrared bands to detect and characterize point sources
        brighter than about 1 mJy in each band, with signal-to-noise ratio
        (SNR) greater than 10, using a pixel size of 2.0". This will achieve
        an 80,000-fold improvement in sensitivity relative to earlier surveys.

        2MASS uses two new, highly-automated 1.3-m telescopes, one at Mt.
        Hopkins, AZ, and one at CTIO, Chile. Each telescope is equipped with a
        three-channel camera, each channel consisting of a 256x256 array of
        HgCdTe detectors, capable of observing the sky simultaneously at J
        (1.25 µm), H (1.65 µm), and Ks (2.17 µm), to a 3{sigma}
        limiting sensitivity of 17.1, 16.4 and 15.3mag in the three bands.

        The 2MASS arrays image the sky while the telescopes scan smoothly in
        declination at a rate of ~1' per second. The 2MASS data "tiles" are 6
        deg. long in the declination direction and one camera frame (8.5')
        wide. The camera field-of-view shifts by ~1/6 of a frame in
        declination from frame-to-frame. The camera images each point on the
        sky six times for a total integration time of 7.8 s, with sub-pixel
        "dithering", which improves the ultimate spatial resolution of the
        final Atlas Images.

        The University of Massachusetts (UMass) is responsible for the overall
        management of the project, and for developing the infrared cameras and
        on-site computing systems at both facilities. The Infrared Processing
        and Analysis Center (IPAC) is responsible for all data processing
        through the Production Pipeline, and construction and distribution of
        the data products. The 2MASS project involves the participation of
        members of the Science Team from several different institutions. The
        2MASS project is funding by the National Aeronautics and Space
        Administration (NASA) and the National Science Foundation (NSF).

    Acknowledging 2MASS in publications:
        Please include the following in any published material that makes use
        of the 2MASS data products:

        "This publication makes use of data products from the Two Micron All
        Sky Survey, which is a joint project of the University of Massachusetts
        and the Infrared Processing and Analysis Center/California Institute of
        Technology, funded by the National Aeronautics and Space Administration
        and the National Science Foundation."

    File Summary:

    File Summary:

           FileName      Lrecl  Records   Explanations

    ×                   80        .   This file
    × ReadMe            80        .   This file
    × out.sam          379     1000   2MASS Point Source Catalogue, sample output
                                    (on a total of 470,992,970 sources)

    See also:
        http://www.ipac.caltech.edu/2mass/ : 2MASS documentation
        VII/233 : The Two Micron All-Sky Survey: Extended sources   (Cutri+ 2003)

    Nomenclature Notes:
        As specified by the IAU recommendations on source nomenclature, the
        object designation is derived from the J2000 sexagesimal coordinates
        of the source and has the form HHMMSSss±DDMMSSs, where HH are the
        hours of right ascension, MM the RA minutes and SSss are the
        centi-seconds of RA. DD are the degrees in declination, MM are DEC
        minutes and SSs the declination deci-seconds. Note that both the RA
        centi-seconds of time and DEC deci-seconds of arc are truncated rather
        than rounded, per the IAU recommendation.

        Note that when several sources have the same identifier, they are
        distinguished by a trailing letter: A, B, C, etc...

    Remark on the Byte-by-byte Description:
        In the Byte-by-byte Description below, the column names differ
        slightly compared to the original description, mainly to follow the
        conventions used in the CDS Standaridzed description of catalogues.
        The original names are written (in parentheses) in the Explanations.

    Byte-by-byte Description of file:  out.sam

       Bytes Format Units    Label    Explanations

       1- 10  F10.6 deg      RAdeg    (ra) Right ascension (J2000)
      12- 21  F10.6 deg      DEdeg    (dec) Declination (J2000) (dec)
      23- 26  F4.2  arcsec   errMaj   (err_maj) Semi-major axis of position error
                                   ellipse
      28- 31  F4.2  arcsec   errMin   (err_min) Semi-minor axis of position error
                                   ellipse
      33- 35  I3    deg      errPA    [0,180] (err_ang) Position angle of error ellipse
                                   major axis (E of N)
      37- 53  A17   ---      2MASS    (designation) Source designation (1)
      55- 60  F6.3  mag      Jmag     ?(j_m) J selected default magnitude (2)
      62- 66  F5.3  mag      Jcmsig   ?(j_cmsig) J default magnitude uncertainty (3)
      68- 72  F5.3  mag      e_Jmag   ?(j_msigcom) J total magnitude uncertainty (4)
      74- 82  F9.1  ---      Jsnr     ?(j_snr) J Signal-to-noise ratio
      84- 89  F6.3  mag      Hmag     ?(h_m) H selected default magnitude (2)
      91- 95  F5.3  mag      Hcmsig   ?(h_cmsig) H default magnitude uncertainty (3)
      97-101  F5.3  mag      e_Hmag   ?(h_msigcom) H total magnitude uncertainty (4)
     103-111  F9.1  ---      Hsnr     ?(h_snr) H Signal-to-noise ratio
     113-118  F6.3  mag      Kmag     ?(k_m) K selected default magnitude (2)
     120-124  F5.3  mag      Kcmsig   ?(k_cmsig) K default magnitude uncertainty (3)
     126-130  F5.3  mag      e_Kmag   ?(k_msigcom) K total magnitude uncertainty (4)
     132-140  F9.1  ---      Ksnr     ?(k_snr) K Signal-to-noise ratio
     142-144  A3    ---      Qflg     (ph_qual) JHK Photometric quality flag (5)
     146-148  I3    ---      Rflg     (rd_flg) Source of JHK default mag (6)
     150-152  I3    ---      Bflg     (bl_flg) JHK components fit to source (7)
     154-156  A3    ---      Cflg     (cc_flg) Artifact contamination, confusion (8)
     158-163  I6    ---      Ndet     (ndet) Number of aperture measurements
                                   (jjhhkk) (9)
     165-169  F5.1  arcsec   prox     Distance between source and nearest neighbour
     171-173  I3    deg      pxPA     ? (pxpa) Position angle of vector from source to
                                   nearest neighbour (E of N)
     175-184  I10   ---      pxCntr   (pxcntr) Sequence number of nearest neighbour
         186  I1    ---      Xflg     [0,2] (gal_contam) Extended source
                                   contamination (10)
         188  I1    ---      Aflg     [0,1] (mp_flg) Association with asteroid or
                                   comet (11)
     190-199  I10   ---      Cntr     (pts_key) Unique source identifier in catalogue
         201  A1    ---      Hemis    [ns] (hemis) Hemisphere of observation
     203-212  A10   ---      Date     (date) Observation date
     214-216  I3    ---      Scan     (scan) Scan number (within date)
     218-224  F7.3  deg      GLON     (glon) Galactic longitude (12)
     226-232  F7.3  deg      GLAT     (glat) Galactic latitude (12)
     234-239  F6.1  arcsec   Xscan    (x_scan) Distance of source from focal plane
                                   centerline
     241-252  F12.4 d        JD       (jdate) Julian date of source measurement (13)
     254-259  F6.2  ---      Jpsfchi  ?(j_psfchi) J band reduced chi2 value of fit
     261-266  F6.2  ---      Hpsfchi  ?(h_psfchi) H band reduced chi2 value of fit
     268-273  F6.2  ---      Kpsfchi  ?(k_psfchi) K band reduced chi2 value of fit
     275-280  F6.3  mag      Jstdap   ?(jmstdap) J standard aperture magnitude (18)
     282-286  F5.3  mag     e_Jstdap  ?(jmsigstdap) error on Jstdap
     288-293  F6.3  mag      Hstdap   ?(hmstdap) H standard aperture magnitude (18)
     295-299  F5.3  mag     e_Hstdap  ?(hmsigstdap) error on Hstdap
     301-306  F6.3  mag      Kstdap   ?(kmstdap) K standard aperture magnitude (18)
     308-312  F5.3  mag     e_Kstdap  ?(kmsigstdap) error on Kstdap
     314-318  I5    arcsec   edgeNS   (distedgens) Distance from the source to the
                                   nearest North or South scan edge
     320-322  I3    arcsec   edgeEW   (distedgeew) Distance from the source to the
                                   nearest East or West scan edge
     324-325  A2    ---      edge     [nsew] (distedgeflg) flag indicating to which
                                   edges the edgeNS and edgeEW values refer
         327  I1    ---      dup      (dup_src) Flag indicating duplicate source (14)
         329  I1    ---      use      (use_src) Use source flag (15)
         331  A1    ---      opt      [0UT] (a) Associated optical source (16)
     333-335  F3.1  arcsec   Dopt     ?(dist_opt) Distance to associated optical source
     337-339  I3    deg      PAopt    [0,360]? (phi_opt) position angle from optical
                                   source to the 2MASS source position
     341-345  F5.2  mag      Bmag     ?(bmopt) Blue magnitude of associated
                                   optical source
     347-351  F5.2  mag      Rmag     ?(vrmopt) Visual or red mag of associated
                                   optical source
         353  I1    ---      Nopt     (nopt_mchs) Number of optical sources within
                                   5arcsec (17)
     355-361  I7    ---      extKey   ?(ext_key) Record Identifier in XSC
     363-367  I5    ---      scanKey  (scan_key) Record Identifier in the Scan
                                   Information Table
     369-375  I7    ---     coaddKey  (coadd_key) Record Identifier in the Atlas Image
                                   Data Table
     377-379  I3    ---      coadd    (coadd) Sequence number of the Atlas Image

    Note (1):  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.
    Note (2): This is the selected "default" magnitude for each band, [JHK].
        If the source is not detected in the band, this 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 origin of the default
        magnitude is given by the first character of the Rflg value
        (Rflg). This column is null if the source is nominally detected in
        the band, but no useful brightness estimate could be made
        (Rflg="9").
    Note (3): This is the corrected photometric uncertainty [JHK]cmsig for
        the default magnitude. If Rflg="2", this is the measurement error
        from the profile-fitting procedure, corrected to be consistent with
        observed repeatability statistics. If Rflg="1" or "4", this is the
        RMS of the brightness measured in aperture photometry on the
        individual frames. If Rflg="3", the uncertainty is derived from the
        residuals to the 1-d radial profile fit to the unsaturated wings of
        the bright star.

        If the value is >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
        (Rflg="0" or "6") or if the source is not measurable (Rflg="9").
    Note (4): Combined, or total photometric uncertainty [JHK]msigcom
        for the default magnitude in that band. The combined uncertainty is
        derived from the following relation:

          e_[JHK]mag = sqrt([JHK]cmsig2 + [JHK]zperr2
                     + fferr2 + [r1normrms2])

        where

        cmsig = Corrected band photometric uncertainty
        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 Rflg="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 band).
    Note (5): Three character flag, one character per band [JHK],
        that provides a summary of the net quality of the default photometry
        in each band, as derived from the Read Flag (Rflg), 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 Qflg 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. Rflg="9" and
            default magnitude is null.

        U = Upper limit on magnitude. Source is not detected in this band
            (Rflg="0"), or it is detected, but not resolved in a consistent
            fashion with other bands (Rflg="6"). A value of Qflg="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 Rflg. When Rflg="0", no flux
            has been detected. When Rflg="6", flux has been detected at the
            location where the images were not deblended consistently in all
            three bands (JHKs).

        F = This category includes Rflg="1" or Rflg="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 e_[jhk]mag 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 (Rflg=2 and
            [jhk]psfchi>10.0), or detections where psf fit photometry did
            not converge and an aperture magnitude is reported (Rflg=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 (Rflg="1" or Rflg="2").

        A = Detections in any brightness regime where valid measurements
            were made (Rflg="1","2" or "3") with
              [jhk]snr>10 AND [jhk]cmsig<0.10857.

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

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

        D = Detections in any brightness regime where valid measurements
            were made (Rflg="1","2" or "3") with
              no [jhk]snr OR [jhk]cmsig requirement.
    Note (6): The read flag indicates the source of J,H,K "default" magnitudes
        as a 3-digit integer, where the 1st digit corresponds to the J band,
        the 2nd to the H band, and the 3rd to the Ks band. Rflg 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 Rflg 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 (Jstdap, Hstdap, Kstdap), 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 Rflg="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.
    Note (7): Blend flag. Three character flag, one character per band [JHK],
        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 (Rflg="2"), or default magnitudes are from aperture
            photometry (Rflg="1" or "4") or saturated star 1-d radial
            profile-fitting (Rflg="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 Bflg 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.
    Note (8): Contamination and confusion flag. Three character flag, one
        character per band [JHKs], 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 Cflg 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 Cflg in any band is an indicator that the
        measurements of that source may be contaminated.
    Note (9): ndet is a six-character flag, two characters per band [JJHHKsKs],
        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 Rflg="1", and to the
        aperture photometry on the 1.3 s "Read_2" exposures if Rflg="2" or
        "4". Sources that are saturated on all of the Read_1 frames
        (Rflg="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.
    Note (10): Extended source "contamination" flag. A value of
        Xflg="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 Ks-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 (Xflg="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'', Xflg does not
        identify all PSC sources with exact XSC counterparts. Use the extKey
        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 extKey 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.
    Note (11): 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 ptsKey.
    Note (12):  Galactic coordinate for 2MASS source derived by precessing
        reconstructed ra and dec to B1950, and performing rotational
        transformation into lII, bII coordinate system. This coordinate should
        not be used as an astrometric reference because it has been rounded to
        0.001 deg.
    Note (13): The Julian Date of the source measurement is accurate to
        ±30seconds. 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.
    Note (14): Used in conjunction with the use 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="1"), or it falls in an overlap region and there were no
            sources detected within 2" of its position in the overlapping
            Tile (use="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.
    Note (15): Used in conjunction with the dup 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="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="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="0" will always have dup="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.
    Note (16): The catalog ID and other association parameters are given for
        the closest optical match found within 5 arcsec. The ID consists of a
        single-letter abbreviation for the catalog (e.g., 'T' for Tycho 2, 'U'
        for USNO-A2.0). '0' means no optical source was found.
    Note (17): 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" does not necessarily mean that there is not an optical
        association within 5 arcsec of the 2MASS position.
    Note (18): the standard aperture magnitude 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
        column is empty if the source is not detected in the band (Rflg="0"),
        or if it is saturated in all of the 1.3 s "Read 2" exposures for the band.

    History:
      * 10-Jun-2003: this ReadMe document was prepared from the documents at
        http://www.ipac.caltech.edu/2mass/releases/allsky/doc/sec2_2a.html
      * 21-Aug-2024: format migration (CDS)
    ================================================================================
    (End)                 Sebastien Derriere, Francois Ochsenbein [CDS]  18-Jun-2003