The following table contains brief descriptions of the parameters provided for each entry in the 2MASS Calibration Point Source Working Databases (Cal-PSWDB, LMC/SMC Cal-PSWDB). The table is organized according to the broad function and utility of the parameters: positional information, photometric information, and source quality information. For Cal-PSWDB and LMC/SMC Cal-PSWDB flag parameters, the meaning of each possible flag value is given, along with some practical information on their usage. The order of the entries in this table is the same as that presented on the IRSA/GATOR query page for this database.
The columns in the following table are:
Column Name | Format | Units | nulls | Description |
---|---|---|---|---|
Primary Positional Information | ||||
ra | %10.6f | deg | no | J2000 right ascension with respect to the USNOA-2.0 Catalog.
Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy. |
dec | %10.6f | deg | no | J2000 declination with respect to the USNOA-2.0 Catalog.
Because calibration scan source astrometry was reconstructed using USNOA-2.0 rather than Tycho 2 as the astrometric reference, there can be systematic offsets of over ~0.5" between calibration scan WDB positions and those in the survey WDB and All-Sky PSC. Survey WDB and PSC positions have better absolute accuracy. |
err_maj | %4.2f | arcsec | no | Semi-major axis length of the one sigma position uncertainty ellipse.
A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference. |
err_min | %4.2f | arcsec | no | Semi-minor axis length of the one sigma position uncertainty ellipse.
A constant factor of of 0.1" on each axis has been RSS'd into the computed position uncertainty error ellipse values to take into account the absolute astrometric uncertainty arising from the use of the USNO-A2.0 catalog as the astrometric reference. |
err_ang | %3d | deg | no | Position angle on the sky of the semi-major axis of the position uncertainty ellipse (East of North) |
Primary Photometric Information | ||||
j_m | %6.3f | mag | yes | Default J-band magnitude, or if the source is not detected in the J-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the first character of the rd_flg value (rd_flg[1]). This column is null if the source is nominally detected in the J-band, but no useful brightness estimate could be made (rd_flg[1]="9"). |
j_cmsig | %5.3f | mag | yes | Corrected photometric uncertainty for the default J-band magnitude. If rd_flg[1]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[1]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[1]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If j_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[1]="0" or "6") or if the source is not measurable (rd_flg[1]="9"). |
j_msigcom | %5.3f | mag | yes | Combined, or total photometric uncertainty for the default J-band magnitude.
The combined uncertainty is derived from the following relation: where
j_cmsig = Corrected J-band photometric uncertainty This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band). |
j_snr | %10.1f | --- | yes | J-band "scan" signal-to-noise ratio. This value is given by the ratio of the J-band flux to the characteristic J-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table j_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the J-band). |
h_m | %6.3f | mag | yes | Default H-band magnitude, or if the source is not detected in the H-band, the 95% confidence upper limit derived from a 4" radius aperture measurement taken at the position of the source on the Atlas Image. The origin of the default magnitude is given by the second character of the rd_flg value (rd_flg[2]). This column is null if the source is nominally detected in the H-band, but no useful brightness estimate could be made (rd_flg[2]="9"). |
h_cmsig | %5.3f | mag | yes | Corrected photometric uncertainty for the default H-band magnitude. If rd_flg[2]="2", this is the measurement error from the profile-fitting procedure, corrected to be consistent with observed repeatability statistics. If rd_flg[2]="1" or "4", this is the RMS of the brightness measured in aperture photometry on the individual frames. If rd_flg[2]="3", the uncertainty is derived from the residuals to the 1-d radial profile fit to the unsaturated wings of the bright star. If h_cmsig > 8.0, it is a flag value indicating that a meaningful uncertainty could not be determined for the source. This column is null if the default magnitude is a 95% confidence upper limit (rd_flg[2]="0" or "6") or if the source is not measurable (rd_flg[2]="9"). |
h_msigcom | %5.3f | mag | yes | Combined, or total photometric uncertainty for the default H-band magnitude.
The combined uncertainty is derived from the following relation: where
h_cmsig = Corrected H-band photometric uncertainty This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band). |
h_snr | %10.1f | --- | yes | H-band "scan" signal-to-noise ratio. This value is given by the ratio of the H-band flux to the characteristic H-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table h_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the H-band). |
k_m | %6.3f | mag | yes | Default Ks-band magnitude, or if the source is not detected in the Ks-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 Ks-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 Ks-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 Ks-band magnitude.
The combined uncertainty is derived from the following relation: where
k_cmsig = Corrected Ks-band photometric uncertainty 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 Ks-band). |
k_snr | %10.1f | --- | yes | Ks-band "scan" signal-to-noise ratio. This value is given by the ratio of the Ks-band flux to the characteristic Ks-band scan noise. The scan noise is the mode of the distribution of flux uncertainties for all point source measurements in a specific 2MASS scan, and is tabulated in the Calibration Scan Information Table k_snr values are capped at 10000000.0. This column is null if the default magnitude is a 95% confidence upper limit (i.e. the source is not detected, or inconsistently deblended in the Ks-band). |
Primary Source Quality Information | ||||
rel | %1s | ---- | no | Reliability flag. Single character flag that is related to the
probability that the extraction is a valid detection of a near infrared
source on the sky at the time of the observation.
This flag does not provide information about the quality of the position or flux measurement. For that, users should refer to the ph_qual, rd_flg, cc_flg and positional and photometric uncertainties. |
ph_qual | %3s | --- | no | Photometric quality flag. Three character flag, one character per band [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 ([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.
|
rd_flg | %3s | --- | no | 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:
|
bl_flg | %3s | --- | no | 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:
|
cc_flg | %3s | --- | no | Contamination and confusion flag. Three character flag, one character
per band [JHKs], that indicates that the extraction is associated
with the predicted position of an image artifact, or that the photometry and/or
position measurements of a source may be contaminated or biased due to
proximity to an image artifact or nearby source of equal or greater brightness.
The cc_flg in each band is
set in hierarchical order according to the following table, in the event
a source is affected by more than one artifact or condition:
Non-zero values the cc_flg in any band is an indicator that the extraction may be a spurious detection of an image artifact, or that measurements of that source may be contaminated. |
ndet | %6s | --- | no | Frame detection statistics. A six-character flag, two characters
per band [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 rd_flg="1", and to the aperture photometry on the 1.3 s "Read_2" exposures if rd_flg="2" or "4". Sources that are saturated on all of the Read_1 frames (rd_flg="3") have N=0 because no aperture photometry was possible. Sources with signal-to-noise ratios >8-9 should be detected on all available frames. Values of N < M for such sources are an indication of possible loss of measurement integrity. Values of N < M, or even N=0, are normal for fainter sources because they are too faint on individual frames to yield a >3 sigma detection. |
gal_contam | %1d | --- | no | Extended source "contamination" flag. A value of gal_contam="2"
indicates that this point source
falls within the elliptical boundary of an All-Sky XSC source defined by the
semi-major axis and ellipticity of the 20 mag arcsec-2
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 (gal_contam="1") Cal-PSWDB sources that are equivalent to sources in the XSC, usually the nuclei of galaxies. The Cal-PSWDB gal_contam values correctly flag all point sources that are found to be resolved relative to a single point-spread-function, regardless of extended source size. The gal_contam="1" flagging in the Cal-PSWDB is correct only for XSC sources with r_k20fe >10'' (I.6.b.xii).
|
mp_flg | %1d | --- | no | Minor Planet Flag. Indicates if this source is
associated with the predicted position of a known minor planet, comet,
planet or planetary satellite. This association does not
guarantee that the Cal-PSWDB source is a detection of the solar system
object.
|
Additional Positional and Identification Information | ||||
pts_key/cntr | %10d | --- | no | A unique identification number for the Working Database entry. This column
is called pts_key in the DVD-ROM and ftp versions of
the Working Databases and cntr in the IRSA/GATOR version.
This sequential number was defined when source records from final data
processing were loaded into the Point
Source Working Database. Pts_key is incremented in order
(or reverse order
depending on the scan direction) of declination within a scan. For this
reason, on average sources with close pts_key values are close
to each other
on the sky, except at Tile boundaries. Pts_key
ordering thus provides a useful mapping of the 2MASS databases on storage
media. Point Source WDB sources are cross-referenced
in the Extended Source WDB,
Known Asteroid Detection List,
Known Comet Detection List, and
Planet and Planetary Satellite Detection List
via the value of pts_key.
Note: pts_key/cntr values in the Cal-PSWDB are not related to pts_key/cntr in the All-Sky Release Catalogs, Survey Reject Tables, or 6x Working Databases/Catalogs. |
hemis | %1s | --- | no | Hemisphere code for the 2MASS Observatory from which this source
was observed.
|
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 lII, bII 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 lII, bII coordinate system. This coordinate should not be used as an astrometric reference because it has been rounded to 0.001 deg. |
x_scan | %6.1f | arcsec | no | Mean cross-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance a source lies west or east of the focal plane centerline. Positive values of x_scan indicate that the source falls west of the centerline and negative values indicate the source is east of the centerline. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky. The x_scan value is useful for identifying sources that may be caused or affected by hot pixel events. |
y_scan | %6.1f | arcsec | no | Mean in-scan focal plane position of the source in the Universal scan (U-scan) coordinate system. This is the approximate distance an extraction lies north of the edge of a scan from which observations were started. Positive values of y_scan indicate that the scan was north-going and the extraction falls north of the starting edge. Negative values indicate the scan was south-going and the extractions falls south of the starting edge. The focal plane position is approximate because it is derived from the mean position of the source detected on up to seven different frames and three different bands. The U-scan coordinate system combines the pixels from the three arrays from each camera, and follows the near-great-circle path of the scan across the sky. |
jdate | %12.4f | day | no | The Julian Date of the source measurement accurate to +30 seconds. This value is extrapolated from the start time of the Calibration scan using the difference between the declinations of the source and the first row in the Tile divided by the scanning rate of the telescope (approximately 5sec). The scanning rate of the two 2MASS telescopes was slightly different because of the need to optimize the dithering of images on the arrays. |
Additional Photometric Information | ||||
j_psfchi | %6.2f | --- | yes | Reduced chi-squared goodness-of-fit
value for the J-band profile-fit photometry
made on the 1.3 s "Read_2" exposures. Unresolved sources that
are well-fit by a single PSF should have j_psfchi~1.0.
Values >2 indicate that the source was not well-fit by a single PSF
and that the profile-fitting
measurement may not accurately capture the flux of the object.
This can occur if the source is resolved, part of a multiple star
group, or is corrupted by a cosmic ray or hot pixel event.
The j_psfchi value is useful as an indicator of photometric quality only if rd_flg[1]="2" for the source, indicating that the default J magnitude (j_m) is from a profile-fitting measurement. A non-null value for j_psfchi may be listed for sources that have rd_flg[1]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in j_m in these cases. This field is null for rd_flg[1]="0","3","4","6" or "9". |
h_psfchi | %6.2f | --- | yes | Reduced chi-squared goodness-of-fit
value for the H-band profile-fit photometry
made on the 1.3 s "Read_2" exposures. Unresolved sources that
are well-fit by a single PSF should have h_psfchi~1.0.
Values >2 indicate that the source was not well-fit by a single PSF
and that the profile-fitting
measurement may not accurately capture the flux of the object.
This can occur if the source is resolved, part of a multiple star
group, or is corrupted by a cosmic ray or hot pixel event.
The h_psfchi value is useful as an indicator of photometric quality only if rd_flg[2]="2" for the source, indicating that the default H magnitude (h_m) is from a profile-fitting measurement. A non-null value for h_psfchi may be listed for sources that have rd_flg[2]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in h_m in these cases. This field is null for rd_flg[2]="0","3","4","6" or "9". |
k_psfchi | %6.2f | --- | yes | Reduced chi-squared goodness-of-fit
value for the Ks-band profile-fit photometry
made on the 1.3 s "Read_2" exposures. Unresolved sources that
are well-fit by a single PSF should have k_psfchi~1.0.
Values >2 indicate that the source was not well-fit by a single PSF
and that the profile-fitting
measurement may not accurately capture the flux of the object.
This can occur if the source is resolved, part of a multiple star
group, or is corrupted by a cosmic ray or hot pixel event.
The k_psfchi value is useful as an indicator of photometric quality only if rd_flg[3]="2" for the source, indicating that the default J magnitude (k_m) is from a profile-fitting measurement. A non-null value for k_psfchi may be listed for sources that have rd_flg[3]="1". However, these are the goodness-of-fits made on saturated star images on the "Read_2" exposures, and do not relate to the aperture photometry magnitude reported in k_m in these cases. This field is null for rd_flg[3]="0","3","4","6" or "9". |
j_m_stdap | %6.3f | mag | yes | J-band "standard" aperture magnitude. This is the
curve-of-growth corrected
average brightness measured in a 4" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated. The
curve-of-growth correction
adjusts to an "infinite" aperture
using a normalization value derived from a series of multi-aperture
measurements made from many stars having the same seeing FWHM
as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures. |
j_msig_stdap | %5.3f | mag | yes | Uncertainty in the J-band standard aperture magnitude.
If there was more than one 1.3 s "Read_2" frame available for
aperture photometry, this the RMS residual of the brightness measured on
the individual frames. If there was only one frame available, this
is the uncertainty derived from the single measurement using the
poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures. |
h_m_stdap | %6.3f | mag | yes | H-band "standard" aperture magnitude. This is the
curve-of-growth corrected
average brightness measured in a 4" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated. The
curve-of-growth correction
adjusts to an "infinite" aperture
using a normalization value derived from a series of multi-aperture
measurements made from many stars having the same seeing FWHM
as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures. |
h_msig_stdap | %5.3f | mag | yes | Uncertainty in the H-band standard aperture magnitude.
If there was more than one 1.3 s "Read_2" frame available for
aperture photometry, this the RMS residual of the brightness measured on
the individual frames. If there was only one frame available, this
is the uncertainty derived from the single measurement using the
poisson statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures. |
k_m_stdap | %6.3f | mag | yes | Ks-band "standard" aperture magnitude. This is the
curve-of-growth corrected
average brightness measured in a 4" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated. The
curve-of-growth correction
adjusts to an "infinite" aperture
using a normalization value derived from a series of multi-aperture
measurements made from many stars having the same seeing FWHM
as the source that is corrected.
This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. This column is null if the source is not detected in the Ks-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" Ks-band exposures. |
k_msig_stdap | %5.3f | mag | yes | Uncertainty in the Ks-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 Ks-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" Ks-band exposures. |
j_m_lgap | %6.3f | mag | yes | J-band large aperture magnitude. This is the
average brightness measured in a 10" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[1]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the J-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures. |
j_msig_lgap | %5.3f | mag | yes | Uncertainty in the J-band large aperture magnitude.
If there was more than one 1.3 s "Read_2" frame
available for aperture photometry, this the RMS residual
of the brightness measured on the individual frames. If
there was only one frame available, this is the uncertainty
derived from the single measurement using the poisson
statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the J-band (rd_flg[1]="0"), or if it is saturated in all of the 1.3 s "Read 2" J-band exposures. |
h_m_lgap | %6.3f | mag | yes | H-band large aperture magnitude. This is the
average brightness measured in a 10" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[2]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the H-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures. |
h_msig_lgap | %5.3f | mag | yes | Uncertainty in the H-band large aperture magnitude.
If there was more than one 1.3 s "Read_2" frame
available for aperture photometry, this the RMS residual
of the brightness measured on the individual frames. If
there was only one frame available, this is the uncertainty
derived from the single measurement using the poisson
statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the H-band (rd_flg[2]="0"), or if it is saturated in all of the 1.3 s "Read 2" H-band exposures. |
k_m_lgap | %6.3f | mag | yes | Ks-band large aperture magnitude. This is the
average brightness measured in a 10" radius aperture centered
on the source position on each of the available 1.3 s "Read_2" frames.
The background
sky reference on each frame is measured in an annular region with
inner radius of 14" and outer radius of 20". Non-detections on
individual frames are included in the average so that the flux is
not statistically overestimated.
No curve-of-growth correction has been applied to this magnitude. This column can contain a measurement even if the default magnitude is from the 51 ms "Read_1" exposures (rd_flg[3]="1"). In this case, the value is the aperture measurement from the available non-saturated 1.3 s "Read_2" exposures. If the extraction is not detected in the Ks-band, this column contains the 95% confidence upper limit to the source brightness, measured from the Atlas Images. This column is null if the source is not detected in the Ks-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" Ks-band exposures. |
k_msig_lgap | %5.3f | mag | yes | Uncertainty in the Ks-band large aperture magnitude.
If there was more than one 1.3 s "Read_2" frame
available for aperture photometry, this the RMS residual
of the brightness measured on the individual frames. If
there was only one frame available, this is the uncertainty
derived from the single measurement using the poisson
statistics of the fluxes in the aperture and sky annulus.
This column is null if the source is not detected in the Ks-band (rd_flg[3]="0"), or if it is saturated in all of the 1.3 s "Read 2" Ks-band exposures. |
j_cal | %5.3f | mag | no | J-band photometric calibration offset. This number was added to each of the the instrumental J-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms. |
h_cal | %5.3f | mag | no | H-band photometric calibration offset. This number was added to each of the the instrumental H-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms. |
k_cal | %5.3f | mag | no | Ks-band photometric calibration offset. This number was added to each of the the instrumental Ks-band magnitudes and upper limits to produce calibrated photometry. It includes the photometric zero point offset and atmospheric extinction correction terms. |
j_skyval | %7.2f | dn | yes | Estimated J-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images. |
h_skyval | %7.2f | dn | yes | Estimated H-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images. |
k_skyval | %7.2f | dn | yes | Estimated Ks-band sky background level, measured in DN, in the sky reference annulus on individual image frames during photometric measurements. This value will be approximately four times the local background level measured on the Atlas Images. |
Additional Source Quality Information | ||||
dist_edge_ns | %5d | arcsec | no | The distance from the source to the nearest North or South scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The first character of the dist_edge_flg indicates to which edge the source is closer. |
dist_edge_ew | %3d | arcsec | no | The distance from the source to the nearest East or West scan edge. The scan edge is defined by the great-circle interpolation between the 3-band coverage corners. The equatorial coordinates of the 3-band coverage corners are given in the Calibration Scan Information Table, referenced by the scan_key. The second character of the dist_edge_flg indicates to which edge the source is closer. |
dist_edge_flg | %2s | --- | no | Two character flag that specifies to which scan edges a source lies closest, and to which edges the dist_edge_ns and dist_edge_ew values refer. The first character encodes the N/S edge: "n" means that dist_edge_ns refers to north scan edge, "s" means that dist_edge_ns refers to the south scan edge. The second character encodes the E/W edge: "e" means that dist_edge_ew refers to the east scan edge, "w" means that dist_edge_ew refers to the west scan edge. |
spos | %5d | ---- | yes | Number of scans covering the position of this extraction. This is computed during the Cal-WDB merging process, using boundaries of each scan that are great-circle interpolations connecting the 3-band coverage corners. Since actual scans "wiggle" slightly in RA due to telescope motions, the actual number of coverages for extractions near scan edges can differ from spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge. |
sdet | %5d | ---- | yes | Total number of detections of this extraction in any band in this Cal-WDB table, in all scans covering its position, determined during the Cal-WDB merging processing. It is possible to have sdet > spos for extractions near scan edges because of the approximations used to determine spos. A null value in this column indicates that the source was not included in the source merging process because of low reliability, or proximity to a scan edge. |
gcntr | %5d | ---- | yes | Unique identification number of the record Merged Point Source Information table corresponding to the merged "group" containing this extraction. The merged "group" contains the combined position and brightness information for all extractions falling within ~1.5" of each other in the Cal-WDB. In confused cases where this extraction appears in more than one group (gcnf>1), the indicated group is the one to which this extraction lies closest. A null value in this column indicates that the source either that the position of this extraction was observed only once, or it was not included in the source merging process because of low reliability, or proximity to a scan edge. |
gcnf | %1d | ---- | yes | Merging confusion flag. Single digit flag that indicates
whether this extraction was associated with more than one group
during the Cal-WDB merging process.
|
Optical Source Association Information | ||||
a | %1s | --- | no | Catalog identifier of an optical source from
the USNO-A2.0 catalog that falls within
approximately 5´´ of the 2MASS source position. Calibration
scan point source extractions were not associated with the
Tycho 2
catalog. The values of this column can be:
Positional association between the 2MASS Cal-PSWDB source and an optical catalog source does not guarantee an identification. Users should consider the separation between the sources, the number of possible optical matches, and consider proper motion when assessing optical counterparts to 2MASS sources. Because Cal-PSWDB sources with optical associations 5´´ from the 2MASS position have a="0", searches on this column are not sufficient to find all Cal-PSWDB sources with associations. Searches for sources where dist_opt is not null, or is null are more reliable for finding sources with or without optical associations, respectively, with the caveat in the following paragraph. The optical association information is unreliable for sources with |dec|>86°, because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has |dec|>86°, a value of a="0" and null values in the other optical association fields, dist_opt, phi_opt, b_m_opt, vr_m_opt, do not necessarily mean that there is not an optical association within 5´´ of the 2MASS position. |
dist_opt | %3.1f | arcsec | yes | Distance separating 2MASS source position and associated optical source within approximately 5´´. This column is null if there is no associated optical source. |
phi_opt | %4d | deg | yes | Position angle on the sky of the vector from the the associated optical source to the 2MASS source position, in degrees East of North. This column is null if there is no associated optical source. |
b_m_opt | %5.2f | mag | yes | Photographic blue magnitude of associated optical source. This column is null if there is no associated optical source. |
vr_m_opt | %5.2f | mag | yes | Photographic red magnitude of the associated optical source. This column is null if there is no associated optical source. |
nopt_mchs | %1d | --- | no | The number of USNO-A2.0 optical sources found within
a radius of approximately 5´´ of the 2MASS position.
The optical association information is unreliable for sources with |dec|>86° because of an error in the 2MASS/USNO-A2.0 position correlation procedure that caused associations to be missed in the vicinity of the equatorial poles. If the source has |dec|>86°, a value of nopt_mchs="0" does not necessarily mean that there is not an optical association within ~5´´ of the 2MASS position. |
Cross-Index Information | ||||
ext_key_1 | %7d | --- | yes | Unique identification number of the record in the Cal-XSWDB that corresponds to this point source. The Cal-XSWDB record with this ext_key value will have the pts_key for this source in its pts_key column. This allows easy cross-referencing between the two catalogs. |
scan_key | %5d | ---- | no | Unique identification number of the record in the Calibration Scan Information Table that corresponds to the calibration scan in which this source was detected. |
coadd_key | %7d | ---- | no | Unique identification number of the record in the Atlas Image Data Table that corresponds to Image in which the position of this source falls. |
coadd | %3d | ---- | no | Sequence number of the Atlas Image in which the position of this source falls. The Image sequence number is number of the frame that is nearest the center of the Image. |
[Last Updated: 2008 February 18, by R. Cutri]