II/281 2MASS 6X Point Source Working Database / Catalog (Cutri+ 2006)
The 2MASS 6X Point Source Working Database / Catalog
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., Zacharias N.
<IPAC, Caltech (2006)>
=2012yCat.2281....0C 2012yCat.2281....0C
ADC_Keywords: Infrared sources ; Photometry, infrared ; Surveys
Description:
A special set of observations that utilized exposure times six times longer
than the main 2MASS survey measurements were conducted in the final year of
2MASS observatory operations. The 2MASS "6x" observations achieved
sensitivities ∼1 mag deeper than the main 2MASS survey, and covered
approximately 590 deg2 of sky in 30 discrete regions.
The 2MASS 6x Point Source Working Databases (6x-PSWDB and 6x-XSWDB)
contain all detections extracted from the raw 6x imaging data during
pipeline data reduction. The 6x WDB entries include reliable detections
of astrophysical sources, as well as spurious detections of noise
excursions, image artifacts and transient events such as meteor trails,
cosmic rays and hot pixels. In addition, the WDBs may contain multiple,
independent detections of objects scanned more than once during the 6x
observations.
The 2MASS 6x Point Source Catalogs (6x-PSC and 6x-XSC) is a subset of
extractions in the 6x-PSWDB that have been identified to be high
reliability source detections, with only one measurement of sources
detected multiple times for uniformity.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
2mass6x.sam 261 500 Sample of 2MASS-6X
--------------------------------------------------------------------------------
See also:
http://http://www.ipac.caltech.edu/2mass/releases/allsky/doc/explsup.html :
2MASS documentation
II/246 : The Two Micron All-Sky Survey: Point sources (Cutri+ 2003)
VII/233 : The Two Micron All-Sky Survey: Extended sources (Cutri+ 2003)
Byte-by-byte Description of file: 2mass6x.sam
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- 2MASS Source designation
18- 27 F10.6 deg RAdeg Right ascension (J2000)
29- 38 F10.6 deg DEdeg Declination (J2000)
40- 44 F5.3 arcsec eeMaj Semi-major axis of the error ellipse
46- 50 F5.3 arcsec eeMin Semi-minor axis of the error ellipse
52- 58 F7.3 deg eerPA Position angle of the error ellipse
60- 65 F6.3 mag Jmag ? 2MASS J magnitude (1.25um)
67- 72 F6.3 mag Hmag ? 2MASS H magnitude (1.65um)
74- 79 F6.3 mag Kmag ? 2MASS Ks magnitude (2.17um)
81- 85 F5.3 mag e_Jmag ? 1-σ total error on Jmag
87- 91 F5.3 mag e_Hmag ? 1-σ total error on Hmag
93- 97 F5.3 mag e_Kmag ? 1-σ total error on Ksmag
99-101 A3 --- Qflg [ABCDEFUXZ] JHK Photometric quality flag (1)
103-105 I3 --- Rflg JHK Read flag (rd_flg) (2)
107-107 I1 --- Xflg [0/2] Extended source contamination flag (3)
109-120 F12.4 d JD Julian Date of observation
122-129 I8 --- gcntr ID of the record Merged Point Source
Information table
131-140 F10.6 deg GLON Galactic longitude
142-151 F10.6 deg GLAT Galactic latitude
153-157 F5.3 mag Jsig ? 1-σ default error on Jmag
159-163 F5.3 mag Hsig ? 1-σ default error on Hmag
165-169 F5.3 mag Ksig ? 1-σ default error on Ksmag
171-180 F10.2 --- Jsnr ? J Band Signal/Noise
182-191 F10.2 --- Hsnr ? H Band Signal/Noise
193-202 F10.2 --- Ksnr ? Ks Band Signal/Noise
204-216 A13 --- Opt ? Optical source designation
218-221 F4.2 arcsec Dopt ? Distance between 2MASS and optical source
223-228 I6 deg PAopt ?=-32768 Position Angle between 2MASS and optical source
230-233 F4.1 mag Bmag ? B magnitude
235-238 F4.1 mag Rmag ? V or R magnitude
240-240 I1 --- Nopt [0/6] Number of optical sources within 5arcsec
242-244 I3 --- Bflg JHK Blend flag (bl_flg) (4)
246-248 A3 --- Cflg JHK Contamination and confusion flag (cc_flg) (5)
250-250 I1 --- Pflg Minor Planet flag (mp_flg) (6)
252-257 I6 --- Ndet Frame detection statistics (7)
259-259 I1 --- cat Catalog flag (1:catalog, 0:archive)
261-261 A1 --- rel [ABCDEF] Reliability flag (8)
--------------------------------------------------------------------------------
Note (1): Photometric quality flag (ph_qual). 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 (rd_flg),
measurement uncertainties ([jhk]_msig), 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).
Z = The detection in this band is positionally associated with the
predicted location of an image artifact. The cc_flg value in this
band will be C,D,G or P.
F = This category includes rd_flg="1" or rd_flg="3" sources where a
reliable estimate of the photometric error, [jhk]_msig, could not
be determined. The uncertainties reported for these sources in
[jhk]_msig 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]_msig<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]_msig<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]_msig<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]_msig
requirement.
Note (2): Read flag. Three character flag, one character per band [JHK],
that indicates the origin of the default magnitudes and uncertainties
in each band ([JHK]mag, [JHK]sig). Values of "1", "2" or "3" generally
indicate the best quality detections, photometry and astrometry.
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 (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 6x 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 7.8s "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 7.8 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 6x-PSWDB/PSC, and is used for
sources that have no saturated pixels in any of the 7.8 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 7.8 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 (jmstdap, hmstdap, kmstdap), 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 6x 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 6x 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 (3): Xflg Extended source "contamination" flag (gal_contam).
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''.
1 = Source is resolved by 2MASS, and is equivalent to a source in the
XSWDB that has a semi-major axis >10'' in size (usually the nuclei
of galaxies). The 6x-PSWDB/PSC Xflg values correctly flag all point
sources that are found to be resolved relative to a single
point-spread-function, regardless of extended source size.
2 = Source falls within the elliptical boundary of an XSC source that
has a semi-major axis >10'' in size. 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.
Note (4): Blend flag (bl_flg). 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 R2 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 6x-PSWDB/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.
Note (5): Contamination and confusion flag. Three character flag, one
character per band [JHK], that indicates that the extraction is
associated with the predicted position of an image artifact, or that
the photometry and/or position measurements of a source may be
contaminated or biased due to proximity to an image artifact or nearby
source of equal or greater brightness. The cc_flg in each band is set
in hierarchical order according to the following table, in the event a
source is affected by more than one artifact or condition:
P = Persistence artifact. Extraction is likely a spurious detection of
a latent image left by a nearby bright star.
G = Dichroic glint artifact. Extraction is likely a spurious detection
of a dichroic glint produced by a nearby bright star.
C = Confusion artifact. Extraction is likely a spurious detection in the
wings of a nearby bright star.
D = Diffraction spike artifact. Extraction is likely a spurious detection
on a diffraction spike from a nearby star.
p = Persistence. Source may be contaminated by a latent image left by a
nearby bright star.
c = Photometric Confusion. Source photometry is biased by a nearby star
that has contaminated the background estimation. This is very common
in high source density regions.
d = Diffraction spike confusion. Source may be contaminated by a
diffraction spike from a nearby star.
s = Electronic stripe. Source measurement may be contaminated by a
stripe from a nearby bright star.
b = Bandmerge confusion. In the process of merging detections in the
different bands for this source, there was more than one possible
match between the different band components. This occurs in regions
of very high source density, or when multiple sources were split in
one band but not another.
0 = Source is unaffected by known artifacts, or is not detected in the band.
Non-zero values the cc_flg in any band is an indicator that the extraction
may be a spurious detection of an image artifact, or that measurements of
that source may be contaminated.
Note (6): 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 6x-PSWDB/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 6x-PSWDB/PSC source is cross-referenced in those Lists via
the value of pts_key.
Note (7): Frame detection statistics. A six-character flag, two characters
per band [JJHHKK], 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 >3σ 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 7.8 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 >3σ detection.
Note (8): Reliability flag. Single character flag that is related to the
probability that the extraction is a valid detection of a near
infrared source on the sky at the time of the observation.
A = P>90%
B = 80%<P<90%
C = 70%<P<80%
D = 50%<P<70%
E = 20%<P<50%
F = P<20%
This flag does not provide information about the quality of the position
or flux measurement. For that, users should refer to the ph_qual, rd_flg,
cc_flg and positional and photometric uncertainties.
--------------------------------------------------------------------------------
(End) Laurent Cambresy [CDS] 27-Feb-2012