The following sections provide a high level description of the contents of each of the Extended Mission Ancillary data sets, and the location of further detailed information about the data processing and analysis of the products. Click on the links above to jump to each of the individual data set descriptions. Table 1 contains a summary of the number of entries in each of the Working Databases (and Catalogs for comparison), the number of Atlas Images in each data set, and the number of 2MASS scans that went into the production of each product.
| Product | Survey WDB | All-Sky Catalogs | Survey "Reject Tables" | 6x WDB | 6x Catalog Subset | Calibration WDB | LMC/SMC Calibration WDB |
|---|---|---|---|---|---|---|---|
| Point Sources | [1,314,981,867]1 | 470,992,970 | 843,988,897 | 24,023,702 | 8,637,702 | 191,464,020 | 5,041,472 |
| Extended Sources | [2,590,500]1 | 1,647,5992 | 943,441 | 247,091 | 84,041 | 403,811 | 9,709 |
| Atlas Images | 4,879,128 | 4,121,439 | --- | 69,687 | 52,671 | 878,760 | 18,504 |
| Scans | 70,712 | 59,731 | --- | 1,328 | 1,031 | 73,230 | 1,542 |
i. Survey Point Source "Reject Table" (PSRT)
All sources extracted during point source processing of
the 70,712 2MASS survey mode scans of the sky were
entered in the Survey Point Source Working Database (PSWDB).
A highly uniform, reliable subset of extractions from the
PSWDB in 59,731 survey scans were selected that comprise the
2MASS All-Sky Point Source Catalog (PSC).
The 2MASS Survey Point Source "Reject Table" (PSRT) contains
astrometry and photometry in the three survey bandpasses for
the 843,988,897 point source extractions from the PSWDB that were not
included in the All-Sky PSC. Extractions in the Survey PSRT
are drawn from all 70,712 survey mode scans, but have
different characteristics in scans selected
for inclusion in the All-Sky PSC than in scans that were not
in the All-Sky Release:
The contents of the Survey PSRT can be summarized as follows:
Because the Survey PSRT contains a large number of
spurious source extractions, this product should be used
cautiously. Users are encouraged to familiarize themselves with the
Cautionary Notes before using
the PSRT,
paying particular attention to the sections discussing source reliability.
As with the 2MASS All-Sky PSC, the reliable Survey PSRT extractions
are predominantly detections of Milky Way stars, but include
point-source processed photometry for virtually all of the resolved
sources found in the Survey Extended Source WDB, as well as a large number
of unresolved, distant galaxies. The brightness of the resolved sources
in the PSRT will be systematically underestimated.
The general properties of
the 2MASS Survey PSRT are presented in A2.2.
The format of the PSRT table is described in
A2.3.a. Source detection and
photometry algorithms used to generate the PSRT are the same
as those used for the All-Sky PSC and are described in
IV.4.
ii. Survey Extended Source "Reject Table" (XSRT)
The 2MASS Survey Extended Source WDB (XSWDB) contains information for
all candidate detections found to be resolved with respect
to a single point-spread-function during processing of 70,712
survey-mode scans. A highly uniform, reliable subset of entries
from the XSWDB in 59,731 survey scans were selected to
comprise the 2MASS All-Sky Extended
Source Catalog (XSC).
The 2MASS Survey Extended Source "Reject Table" (XSRT) contains
astrometry, photometry and basic shape information for the
943,441 extended source candidates in the PSWDB that were
not included in the All-Sky XSC. Extractions in the Survey XSRT are
drawn from all 70,712 survey mode scans, but have different
characteristics in scans selected for inclusion
in the All-Sky XSC than in scans that were not in the All-Sky Release:
The contents of the Survey XSRT can be summarized as follows:
Note that the Survey XSRT does not contain the
Large Galaxy entries that are found
in the XSC. These entries were constructed using special processing that
combined images from multiple survey scans and are not products
of the standard survey scan data processing.
The general properties of
the 2MASS Survey XSRT are presented in
Section A2.2. The format of the WDB table is described in
Section A2.3b. Source detection and
photometry algorithms used to generate the XSRT are the same
as those used for the All-Sky XSC and are described in
IV.5.
iii. Full Survey Image Atlas
The 2MASS Full Survey Image Atlas contains 4,879,128 calibrated
FITS images in the three survey bandpasses constructed from
70,712 scans of 8.5´ × 6°
Survey Tiles.
The Survey Atlas is the superset of images from which the All-Sky Release
Image Atlas was drawn.
The image data from each survey scan are divided into twenty-three
separate Atlas Images in each band.
Twenty-two of these are 512×1024 (1"/pix) in size, and one
is 512×698 (1"/pixel).
The J, H and Ks images for each region of sky are
resampled to the same scale and registered to facilitate 3-color
investigations. Positional and photometric calibration data
are carried in the FITS header for each image, which
is described in II.4.a.
2MASS Full Survey Atlas Images are accessible via the
2MASS Image Services which are administered by the
Infrared Science Archive (IRSA).
These services allow interactive viewing and retrieval of one or more images
and include an inventory mode that lists all images that cover a
point or region on the sky. The inventory mode is a particularly
useful tool to determine if more than one scan, and its Atlas Images,
are available for a particular region of the sky.
i. 6x Point Source Working Database and Catalog (6x-PSWDB and 6x-PSC)
The 2MASS Long Exposure (6x) Point Source Working Database (6x-PSWDB)
contains astrometry and photometry in the three survey bandpasses for
24,023,702
"sources" extracted from 1,328 scans of the sky
taken with exposures six time longer than used in the primary survey.
The 6x-PSWDB is the primary record of the pipeline point source
processing of the long exposure data.
A 6x Point Source Catalog (6x-PSC) was drawn from the 6x PSWDB
using criteria that are analogous to those that were used to draw
the All-Sky PSC from the Survey Point Source WDB. The 6x-PSC is
a view on the 6x-PSWDB that contains
8,637,594 sources drawn from 1,031 of the long exposure scans.
As with the All-Sky Release PSC, the 6x-PSC is a more uniform and reliable
representation of the near infrared sky that contains only
one entry for each source (i.e. one detection of objects
scanned and detected multiple times is selected for the Catalog).
Unlike the All-Sky Release PSC,
the 6x-PSC is not released as a separate table but as a subset of the
larger 6x-PSWDB. 6x-PSC sources are identified in the 6x-PSWDB using
the cat column found in
the source record. 6x-PSC sources have a value of cat="1".
6x-PSWDB extractions not included in the Catalog
(i.e. the 6x Point Source Reject File) have cat="0".
In addition to all detections that comprise the 6x-PSC, the
full 6x-PSWDB contains:
Because the 6x Point Source WDB contains a large number of
false source extractions, this product should be used
cautiously. Users are encouraged to familiarize themselves with the
Cautionary Notes before using the 6x-PSWDB
paying particular attention to the sections discussing source reliability.
The general properties of
the 2MASS 6x PSWDB are presented in A3.2.
The format of the 6x-PSWDB/6x-PSC table is described in
A3.3a Source detection and
photometry algorithms used to generate the 6x-PSWDB are
described in A3.5. Scan and source
selection criteria used to identify sources that constitute the
6x-PSC are described in A3.7.
ii. 6x Extended Source Working Database and Catalog (6x-XSWDB and 6x-XSC)
The 2MASS 6x Extended Source WDB (6x-XSWDB) contains astrometry, photometry
in the three survey bandpasses and basic shape information for
247,091 candidate "sources" found to be resolved with respect
to a single point-spread-function during processing of 1,328
special scans of the sky taken with exposures six time longer than
used in the primary survey. The 6x Extended Source WDB is the primary
archive of the pipeline extended source processing of the survey
data.
A 6x Extended Source Catalog (6x-XSC) was drawn from the 6x-XSWDB
using criteria that are analogous to those that were used to draw
the All-Sky XSC from the Survey Extended Source WDB. The 6x-XSC, which
contains 84,041 sources drawn from 1,031 of the long
exposure scans,
is of higher reliability than the 6x-XSWDB, and is intended to contain only
one entry for each source on the sky. Unlike the All-Sky Release XSC,
the 6x-XSC is not released as a separate table but as a subset of the
larger 6x-XSWDB. 6x-XSC sources are identified in the 6x WDB as having a
cat
flag value of "1". 6x-XSWDB entries not in the
6x-XSC have cat=0.
The 6x-XSWDB contains:
Note that the 6x-XSWDB does not contain any
Large Galaxy entries that are found
in the All-Sky XSC. These entries were constructed using special processing
that combined images from multiple survey scans and are not products
of the standard 6x scan data processing.
The general properties of
the 2MASS 6x Extended Source WDB are presented in
Section A3.2. The format of the WDB table is described in
Section A3.3b. Source detection and
photometry algorithms used to generate the Extended Source WDB are
described in A3.5.a.
Scan and source
selection criteria used to identify sources that constitute the
6x-XSC are described in A3.6.
iii. 6x Image Atlas
The 2MASS 6x Image Atlas contains 69,687 calibrated
FITS images in the three survey bandpasses constructed from
1,328 scans of the sky taken with exposures six time longer than
used in the primary survey. Two types of
6x scans were made:
6° long (in declination) scans (dubbed "LSC") that covered
regions analogous to Survey Tiles,
and 1° long (in declination) scans (dubbed "LCA") that
covered regions similar in size to Calibration
Tiles.
The image data from each 6° LSC scan are divided into twenty-three
separate Atlas Images in each band. Twenty-two of these are
512×1024 (1"/pix) in size, and one ranges in size
from 512×648 to 512×670 (1"/pixel).
For the 1° long LCA 6x scans, the images data are
divided into four separate Atlas Images in each band. Three
are 512×1024 (1"/pix) in size, and one is shorter, having
sizes that range from 512×818 to 512×841 (1"/pixel).
The J, H and Ks images for each region of sky are
resampled to the same scale and registered to facilitate 3-color
investigations. Positional and photometric calibration data
are carried in the FITS header for each image, which
has the same format as those of the Survey Atlas Images, and
is described in II.4.a.
2MASS 6x Atlas Images are accessible via the
2MASS Image Services which are administered by the
Infrared Science Archive (IRSA).
These services allow interactive viewing and retrieval of one or more images
and include an inventory mode that lists all images that cover a
point or region on the sky. The inventory mode is a particularly
useful tool to determine if more than one scan, and its Atlas Images,
are available for a particular region of the sky.
i. Calibration Point Source Working Database
(Cal-PSWDB) and LMC/SMC Calibration Point Source Working Database
(LMC/SMC Cal-PSWDB)
The 2MASS Calibration Point Source Working Database (WDB) contains
astrometry and photometry in the three survey bandpasses for
191,464,020
"sources" extracted from 73,230 1° long (in declination) scans
of the 35 Calibration Fields (or Tiles).
2MASS calibration observations were made using the same scanning technique
and exposure time as the main survey observations, and calibration
scan data were reduced using virtually the same pipeline processing system
that was used to reduce the survey data (see A4.4).
The Calibration Point Source WDB is the primary record of the pipeline
point source processing of the calibration data.
The LMC/SMC Calibration Point Source Working Database (WDB) contains
astrometry and photometry in the three survey bandpasses for
5,041,472
"sources" extracted from 1,542 1° long (in declination) scans
of five additional Calibration Fields (or Tiles)
located in and around the LMC/SMC that were observed in support
of the long exposure (6x) observations of those
regions. The data acquisition and processing for these five fields were the
same as for the primary survey calibration fields.
The Cal-PSWDB and LMC/SMC Cal-PSWDB contain:
Because the Cal-PSWDBs contain a large number of
spurious source detections, this product should be used
cautiously. Users are encouraged to familiarize themselves with the
Cautionary Notes before using the Cal-PSWDB,
paying particular attention to the sections discussing source reliability.
The general properties of
the 2MASS Cal-PSWDBs are presented in A4.2.
The format of the Cal-PSWDB table is described in
A4.3.a. Source detection and
photometry algorithms used to generate the Calibration Point Source WDBs are
the same as those used for the All-Sky PSC and are described in
A4.4. Photometric and astrometric
calibration of the Calibration scan data was handled differently
than the Survey data, and is discussed in A4.4.
ii. Calibration Extended Source Working Database (Cal-XSWDB)
The 2MASS Calibration Extended Source WDB (Cal-XSWDB) contains astrometry,
photometry in the three survey bandpasses and basic shape information for
403,811 candidate "sources" found to be resolved with respect
to a single point-spread-function during processing of 73,230
1° long (in declination) scans of the 35
Calibration Fields (or Tiles).
2MASS calibration observations were made using the same scanning technique and
exposure time as the main survey observations, and calibration scan data were
reduced using virtually the same pipeline processing system that was used to
reduce the survey data (see A4.4).
The Calibration Extended Source WDB is the primary
archive of the pipeline extended source processing of the calibration
observation data.
The LMC/SMC Calibration Extended Source Working Database (WDB) contains
astrometry and photometry in the three survey bandpasses for
9,709
"sources" extracted from 1,542 1° long (in declination) scans
of five additional Calibration Fields (or Tiles)
located in and around the LMC/SMC that were observed in support
of the long exposure (6x) observations of those
regions. The data acquisition and processing for these five fields were the
same as for the primary survey calibration fields.
The Cal-XSWDB and LMC/SMC Cal-XSWDB contain:
Note that the Cal-XSWDB and LMC/SMC Cal-XSWDB doe not contain the
Large Galaxy entries that are found
in the All-Sky XSC. These entries were constructed using special post
processing that combined images from multiple survey scans and are
not products of the standard calibration scan data reduction.
The general properties of
the 2MASS Cal-XSWDBs are presented in
A4.2. The format of the Cal-XSWDB tables
are described in A4.3b. Source detection
and photometry algorithms used to generate the Cal-XSWDBs are the
same as those used for the All-Sky XSC and are described in
IV.5.
iii. Calibration Scan Image Atlas
The 2MASS Calibration Scan Image Atlas contains 878,769 calibrated
FITS images in the three survey bandpasses constructed from
73,230 1° long (in declination) scans of the 35
Calibration Fields (or Tiles).
The 2MASS LMC/SMC Calibration Scan Image Atlas contains 18,504
calibrated
FITS images in the three survey bandpasses constructed from
1,542 1° long (in declination) scans of the five
special Calibration Fields (or Tiles)
located in and around the LMC/SMC that were observed in support
of the long exposure (6x) observations
of those regions.
The image data from each 1° Calibration scan are divided
four separate Atlas Images in each band. Three
are 512×1024 (1"/pix) in size, and one is shorter, having
sizes that range from 512×648 to 512×673 (1"/pixel).
The J, H and Ks images for each region of sky are
resampled to the same scale and registered to facilitate 3-color
investigations. Positional and photometric calibration data
are carried in the FITS header for each image, which
has the same format as the Survey Atlas Image headers, and
is described in II.4.a.
2MASS Calibration Atlas Images are accessible via the
2MASS Image Services which are administered by the
Infrared Science Archive (IRSA).
These services allow interactive viewing and retrieval of one or more images
and include an inventory mode that lists all images that cover a
point or region on the sky. Because of the highly redundant nature of
the Calibration Image data, the inventory mode is not as useful
as for the Survey or 6x data since it will usually return a large number
of images covering any position in a Calibration field.
a. Survey Extracted Source "Reject Tables" and Full Image Atlas
b. Long Exposure ("6x") Working Databases/Catalogs and Atlas Images
c. Calibration Scan Working Databases and Atlas Images
d. Merged Source Information
| Product | Survey | 6x | Calibration | LMC/SMC Calibration |
|---|---|---|---|---|
| Merged Point Source Information | 165,942,357 | 4,771,737 | 456,480 | 35,278 |
| Merged Point Source Cross-Reference | 396,697,288 | 12,267,173 | 204,143,440 | 4,250,232 |
| Merged Extended Source Information | 406,636 | 30,252 | 2,146 | 101 |
| Merged Extended Source Cross-Reference | 960,841 | 76,636 | 473,971 | 8,660 |
i. Merged Point Source Information Tables
The 2MASS Survey, 6x, Calibration and LMC/SMC Calibration Merged
Point Source Information Tables
contain combined position and brightness data
for sources detected more than once in each of the
respective data sets. All sightings of a source are identified by
performing a positional autocorrelation of each Point Source WDB,
and finding groups of extractions from different scans that fall within
a 1.5" correlation radius. For each group of positionally associated
extractions, the Merged Source Information tables contain
the variance-weighted mean positions, mean and variance-weighted mean fluxes
in the three survey bandpasses, various statistics on the distribution
of positions and fluxes of all the sightings, and confirmation
statistics summarizing the number of times a source was detected
in a given WDB and the estimated number of times the mean position
of the source was scanned. The source merging process
is limited by possible source
proper motion,
confusion with intermittently resolved multiple sources and noise,
and the internal consistency of 2MASS source position
reconstruction.
As shown in Table 2, the Survey, 6x, Calibration and
LMC/SMC Calibration Scan
Merged Point Source Tables contain 165,942,357, 4,771,737,
456,480 and 35,278 entries, respectively. These are much smaller
than the sizes of each of the respective Point Source WDBs given
in Table 1 for several reasons:
The Merged Point Source Information Tables are designed to be used
in conjunction with the respective WDBs as a source of additional data
for selected objects, rather than as a replacement for them.
For example, you cannot necessarily query the Survey Merged
Point Source Information Table to find a complete list
of detections down to some flux level in a particular region
of the sky, even though the Survey observations covered
the entire sky (okay, 99.998% of the sky). The more appropriate
use is to identify objects of
interest in the Catalogs or WDBs, and if the sources
were detected more than once, use the Merged Source
Information tables to obtain improved photometry and positions,
or to investigate if the sources have moved or has varied in brightness.
Within the Survey, 6x, Calibration and LMC/SMC Calibration Merged
Point Source Information
Tables, each entry corresponds to an associated group of extractions
and is assigned a unique identifier,
gcntr.
This identifier is cross-referenced in the individual Survey,
6x and Calibration Scan Point Source WDB entries. Each WDB entry
belonging to a merged group of extractions also carries
the number of times the source was detected
(sdet) and an estimate of the
number of times the merged source position was scanned within
a given data set (spos).
The general WDB merging process is described in
Appendix 6. The contents and formats of the
Survey, 6x, Calibration and LMC/SMC Calibration Merged Point Source
Information Tables are
given in A6.3a.
ii. Merged Point Source Cross-Reference (Link) Tables
The Survey, 6x, Calibration and LMC/SMC Calibration Scan Merged Point
Source Cross-Reference
Tables contain the information linking each associated group of extractions
with their individual WDB entries. Each table contains one row
for each WDB extraction that has been associated with a merged
source group. Each row in the tables provides
the unique merged group identifier (gcntr), the
unique WDB identifier (cntr/pts_key) and the number of
groups with which that particular WDB extraction has been associated
(ngrp). A WDB extraction may be associated with more than one
merged group in confused situations. The cntr/pts_key
values for such WDB extractions will appear more than once
in the Cross-Reference Table, accompanied by the gcntr
of each of the groups to which it has been associated.
As seen in Table 2, the Survey, 6x and Calibration Scan Merged
Point Source Cross-Reference Tables contain 396,697,288,
12,267,173, 204,143,440 and 42,50,232 entries, respectively.
Contrasting these numbers with the number of entries in the respective
Point Source Merged Information Tables gives the approximate
mean number of independent detections of each merged source
within each WDB. For the Survey and 6x data sets this
ranges from 2-3 detections per group. For the highly redundant
Calibration Scan data, the mean number of detections is ~470,
emphasizing the value of these data as a source for
precision photometry and time domain studies.
The Merged Point Source Cross-Reference Tables are discussed
in the context of the general WDB merging process in
Appendix 6. The formats of the
Survey, 6x, Calibration and LMC/SMC Calibration Cross-Reference Tables
are the same,
and are given in A6.3c.
iii. Merged Extended Source Information Tables
The 2MASS Survey, 6x, Calibration and LMC/SMC Calibration Merged
Extended Source Information
Tables contain combined position and brightness data
for resolved sources detected more than once in each of the
respective data sets. All sightings of a source are identified by
performing a positional autocorrelation of each Extended Source WDB,
and finding groups of extractions from different scans that fall within
a 5" correlation radius. For each group of positionally associated
extractions, the Merged Source Information Tables contain
the variance weighted mean positions, mean and variance weighted mean selected
fluxes in the three survey bandpasses, average basic shape information,
various statistics on the distribution of positions, fluxes, and
shape parameters of all the sightings, and confirmation
statistics summarizing the number of times a source was detected
in a given WDB and the estimated number of times the mean position
of the source was scanned. The source merging process
is limited by possible
confusion with intermittently resolved multiple sources and noise,
and the internal consistency of 2MASS source position
reconstruction.
As shown in Table 2, the Survey, 6x and Calibration Scan
Merged Extended Source Information Tables contain 406,636,
30,252, 2,146 and 101 entries, respectively.
These are much smaller
than the sizes of each of the Extended Source WDBs given
in Table 1 for several reasons:
The Merged Extended Source Information Tables are designed to be used
in conjunction with the respective WDBs as a source of additional data
for some sources, rather than as a replacement for them.
For example, you cannot necessarily query the Survey Merged
Extended Source Information Table to find a complete list
of detections down to some flux level in a particular region
of the sky, even though the Survey observations covered
the entire sky. The more appropriate
use is to identify objects of
interest in the WDBs (or Catalogs), and if they were detected
more than once, use the Merged Source
Information tables to obtain improved photometry and positions,
or to investigate if the sources have varied in brightness.
Within the Survey, 6x and Calibration Merged Extended Source Information
Tables, each entry corresponds to an associated group of extractions
and is assigned a unique
identifier, gcntr.
This identifier is cross-referenced in the individual Survey,
6x and Calibration Scan Extended Source WDB entries. Each WDB entry
belonging to a merged group of extractions also carries
the number of times the source was detected
(sdet) and an estimate of the
number of times the merged source position was scanned within
a given data set (spos).
The general WDB merging process is described in
Appendix 6. The contents and formats of the
Survey, 6x and Calibration Merged Extended Source Information Tables are
given in A6.3b.
iv. Merged Extended Source Cross-Reference (Link) Tables
The Survey, 6x and Calibration Scan Merged Extended Source Cross-Reference
Tables contain the information linking each associated group of extractions
with their individual WDB entries. Each table contains one row
for each WDB extraction that has been associated with a merged extended
source group. Each row in the tables provides
the unique merged group identifier (gcntr), the
unique WDB identifier (cntr/pts_key) and the number of
groups with which that particular WDB extraction has been associated
(ngrp). A WDB extraction may be associated with more than one
merged group in confused situations. The cntr/pts_key
values for such WDB extractions will appear more than once
in the Cross-Reference Table, accompanied by the gcntr
of each of the groups to which is has been associated.
As seen in Table 2, the Survey, 6x and Calibration Scan Merged
Extended Source Cross-Reference Tables contain 960,841,
76,636, 473,971 and 8,660 entries, respectively.
Contrasting these numbers with the number of entries in the respective
Extended Source Merged Information Tables gives the approximate
mean number of independent detections of each merged source
within each WDB. For the Survey and 6x data sets this
ranges from 2-3 detections per group. For the highly redundant
Calibration Scan data, the mean number of detections is ~220,
emphasizing the value of these data as a source for
precision photometry and time domain studies.
The Merged Extended Source Cross-Reference Tables are discussed
in the context of the general WDB merging process in
Appendix 6. The formats of the
Survey, 6x, Calibration and LMC/SMC Calibration Cross-Reference Tables
are the same,
and are given in A6.3c.
e. Combined Calibration Scan Images and Source Lists
| Product | Number |
|---|---|
| Images | 735 |
| Extracted Sourcesa | 246,760 |
Notes to Table 3:
a - Includes extractions identified
as spurious detections of image artifacts.
i. Combined Calibration Scan Images
The Combined Calibration Scan images are a set of J, H and Ks
FITS images that were produced
by combining the Atlas Images from the 600-3700 individual scans
of each of the 35 Calibration Fields
acquired during the Survey.
The combined images are the deepest observations enabled by 2MASS,
reaching nominal sensitivities 3.5 to 4.5 magnitudes deeper
than the Survey or single Calibration scan measurements (not
taking into account confusion which can be significant in
the Galactic Plane fields).
There are 21 FITS images available for each Calibration field.
In each of the 3 survey bands, J, H and Ks, the
images are:
The north- and south-going scan data were combined separately
for each field to facilitate the identification of bright star latent images
(IV.7).
Latents trail in opposite directions from the parent star
in the different scan directions. Within each calibration
observation (set of six calibration scans), each scan was
displaced by 5" in RA from the previous scan to minimize
systematic pixel effects. These offsets, combined with small telescope
pointing variations resulted in a spread in the footprint of
the Calibration Scans on the sky. The full-area combined images
include most of the area covered by all scans, regardless of
the depth of coverage. The masked combined images
are truncated to include only the area covered by at least 30%
of the available scans.
Production of the Combined Calibration Scan Images is described
in Appendix 7. This was accomplished
by registering the images from each individual scan onto a common
position grid (A7.2a), identifying and filtering
out the noisiest or otherwise contaminated scans
(A7.2d), scaling the images from each scan
according to the measurement sensitivity (A7.2c)
and forming the noise-variance-weighted averages of the selected images.
The FITS headers of the combined images contain full WCS information and
photometric zero points.
Users are strongly encouraged to familiarize themselves with the
Cautionary Notes concerning the Combined Calibration Scan Images
given in A7.1.b.
The Combined Calibration Scan FITS images can be accessed
via the web-based Combined Calibration
Field Data Retrieval Page (A7.4).
ii. Combined Calibration Scan Extracted Source Lists
The Combined Calibration Scan Extracted Source Lists contain positional
and three-band photometric data for 246,760 sources detected on
the deep, Combined Calibration Scan FITS Images.
Preparation of the extracted source lists is described in
A7.3.
Conservative source detection was performed separately on the north- and
south-going combined images. The final source lists include only sources
that were detected on both directions - this eliminates a large fraction
of the spurious detections of random noise and latent images.
Simple circular aperture photometry of extracted sources, bootstrapped
to the measured brightness of the 2MASS Survey calibration stars
in each field, is provided.
The format of the extracted source tables is presented in
A7.3d. The general properties of
combined calibration scan extracted source lists are presented
in A7.5, including source counts,
comparisons with the 2MASS All-Sky Point Source photometry
and astrometry.
It is expected that most users will perform custom
PSF-fitting source extraction on the Combined Calibration Images
because of the high degree of confusion and complexity in the fields.
Therefore, the extracted source lists are intended
to be "introductory" only, and to provide guidance on issues such
as photometric and astrometric calibration. Source
detection used a relatively conservative SNR~5 threshold.
The circular aperture photometry will be adequate for isolated, unresolved
sources, but will be biased for extended and/or multiple objects
that will be better characterized using specialized apertures
and source deblending. The extracted
source lists have not been rigorously cleaned of spurious artifact
detections. The lists do contain a "confusion and contamination"
flag, cc_flg, that is analogous
to that in the Catalogs, Reject Tables and Working Databases.
However, there may be unflagged artifact detections in the lists.
Users are strongly encouraged to review the
Cautionary Notes concerning the Combined Calibration Scan Extracted
Source Lists given in A7.1.b.
The Combined Calibration Scan Source Lists may be accessed
via the web-based Combined Calibration Field
Data Retrieval Page (A7.4), or using the
GATOR
Catalog Access Service at the
Infrared Science Archive.
[Last Updated: 2010 February 10; by R. Cutri]
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