Definition of values for flags, taken from the 2MASS web site.

RD_FLG:
Read flag. Three character flag, one character per band [JHKs], 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:
Blend flag. Three character flag, one character per band [JHKs], 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:
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 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. 


PH_QUAL:
Photometric quality flag. Three character flag, one character per band [JHKs],
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
([JHKs]_MAG_SIG), 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 (JHKs).
* "F" - This category includes rd_flg="1" or rd_flg="3" sources where a
reliable estimate of the photometric error, [JHKs]_MAG_SIG could not be
determined. The uncertainties reported for these sources in [JHK]_MAG_SIG
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 [JHKs]_MAG_SIG<0.10857.
* "B" - Detections in any brightness regime where valid measurements were
made (rd_flg="1","2" or "3") with [jhk]_snr>7 AND [JHKs]_MAG_SIG<0.15510.
* "C" - Detections in any brightness regime where valid measurements were
made (rd_flg="1","2" or "3") with [jhk]_snr>5 AND [JHKs]_MAG_SIG<0.21714.
* "D" - Detections in any brightness regime where valid measurements were
made (rd_flg="1","2" or "3") with no [jhk]_snr or [JHKs]_MAG_SIG requirement.

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