II. User's Guide to the 2MASS All-Sky Data Release

6. Ancillary Files

a. Scan Information Table

The Scan Information Table contains parameters describing and derived from each observation of the 59,731 Tiles (see III.2a) that comprise the All-Sky Data Release. These parameters include Tile identification, and location on the sky, observatory and instrument specifications, measured environmental and derived sky conditions, and statistics and quality information regarding the scan. The Scan Information Table Format page describes each column in the table, and provides links to more detailed descriptions of the parameters when they are available.

Each entry in the Scan Information Table contains a unique index, scan_key. Entries in the Point and Extended Source Catalogs are cross-referenced to the Scan Information Table listings via the scan_key value.

The Scan Information Table is accessible using the IRSA/GATOR online query engine. It is also available in database-readable ascii form via download from anonymous ftp and on the All-Sky Release DVD-ROM (I.4).

Table 1 - Scan Information Table Format

b. Atlas Image Information Table

The Atlas Image Information Table contains metadata and derived information for each 1,373,813 registerd sets of J, H and Ks Atlas Images (see II.4) in the All-Sky Data Release. The columns in this table provide descriptions, locations and calibration information for each image, as well as parameters such as seeing and background derived from measurements of the images during data processing. The Atlas Image Information Table Format page describes each column in the table, and provides links to sections of the Explanatory Supplement that contain detailed descriptions of the parameters when they are available.

Each entry in the Atlas Image Information Table contains a unique index, coadd_key. Entries in the Point and Extended Source Catalogs are cross-referenced to the Atlas Image Information Table listings via the coadd_key value.

The Atlas Image Information Table is accessible using the IRSA/GATOR online query engine, and is also available in database-readable form via anonymous ftp and on the All-Sky Release DVD-ROM.

c. Known Asteroid Association List

The All-Sky Release PSC contains 15,964 sources that are positionally associated with the predicted positions of known asteroids. These sources were identified during scan data processing by determining which known asteroids were within the boundaries of a 2MASS Tile when it was scanned, and searching for positional correlations between the predicted positions of those objects and extracted 2MASS sources. Section IV.9 contains a description of this procedure, the asteroid ephemerides and position prediction methods used. Association between predicted asteroid and 2MASS source positions does not imply an identification, particularly at low galactic latitude where chance association with background stars is likely.

The Known Asteroid Association List gives for each asteroid that was associated with a source in the All-Sky Release PSC object identification, orbital data used to predict positions and visual brightness, and abridged PSC data for the source. Cross-reference to the full PSC source entry (and in some cases the XSC) is made via the pts_key and ext_key columns. The description of each column is provided in the table header. Note that the names of some columns in the table header have been abbreviated from their full PSC names to save space. The full PSC column names are given in the definitions in these cases.

A number of asteroids have multiple entries in this table because they were detected more than once during the Survey due to their motion, and appear in the PSC multiple times. For example, (52) Europa appears in the PSC five times, its position having been scanned on 1998 September 19 and 25 UT, twice on 2000 February 25 UT, and once again on 2000 March 14 UT.

Table 3 - Known Asteroid Association List

d. Known Comet Association List

The All-Sky Release PSC contains 46 sources that are positionally associated with the predicted positions of known comets. Eight of these were resolved 2MASS detections and are thus also included in the All-Sky Release XSC. These sources were identified during scan data processing by determining which known comets were within the boundaries of a 2MASS Tile when it was scanned, and searching for positional correlations between the predicted positions of those objects and extracted 2MASS sources. Users are encouraged to read Section IV.9 for a detailed description of this procedure, for details concerning comet ephemerides and position prediction. Association between predicted comet and 2MASS source positions does not imply an identification, particularly at low galactic latitude where chance association with background stars is likely.

The Known Comet Association List gives for each comet that was associated with a source in the All-Sky Release PSC object identification, orbital data used to predict positions and visual brightness, and abridged PSC data for the source. Cross-reference to the full PSC and XSC source entries is made via the pts_key and ext_key columns. The description of each column is provided in the table header. Note that the names of some columns in the table header have been abbreviated from their full PSC names to save space. The full PSC column names are given in the definitions in these cases.

Several comets appear in this table more than once because they were detected more than once during the Survey due to their motion, and appear in the PSC and/or XSC multiple times.

Table 4 - Known Comet Association List

e. Known Planet and Satellite Association List

The All-Sky Release PSC contains detections of Uranus, Neptune and Pluto and 14 satellites of these planets and Jupiter. Jupiter was also scanned during Survey operations, but it was so bright that its glare effectively washed out the scan data that covered it. That region of the sky was reobserved at a later time after Jupiter had moved on, and Jupiter's scan was not included in the All Sky Release.

Planetary detections were identified during scan data processing by determining which known planets were within the boundaries of a 2MASS Tile when it was scanned, and searching for positional correlations between the predicted positions of those objects and extracted 2MASS sources. Planetary satellite associations were made manually after pipeline data processing was complete, using a similar procedure. Users are encouraged to read Section IV.9 for a detailed description of these procedures, for details concerning planet ephemerides and position prediction, and for important caveats concerning the associations.

The Known Planet and Satellite Association List gives for each planet and satellite was associated with a source in the All-Sky Release PSC object identification, orbital data used to predict positions and visual brightness, and abridged PSC data for the source. Cross-reference to the full PSC source entry is also provided via the pts_key columns. The description of each column is provided in the table header. Note that the names of some columns in the table header have been abbreviated from their full PSC names to save space. The full PSC column names are given in the definitions in these cases.

Uranus and several of its satellites appear twice in this table because their positions were scanned twice at different times during the Survey, and they have multiple entries in the PSC. However, Uranus is resolved so it was not reliably extracted each time it was observed.

Table 5 - Known Planet and Satellite Association List

f. Extended Source Spatial Coverage Maps

The effective spatial coverage of the XSC was limited by the presence of foreground stars. Bright stars mask out regions in large halos and covering long diffraction spike around their locations. The masked area was computed during extended source processing (see IV.5), and the fractional coverage for each 2MASS Atlas Image in each band was derived. The fractional coverage per image was used to generate large scale effective coverage maps for the XSC. These coverage maps are available in GIF previews and FITS formats in the link above.

g. PSC and XSC Anomaly Files

Every effort has been made to remove unreliable sources from the Catalogs, and to flag sources that might be contaminated by image artifacts. However, the sheer volume of the 2MASS image and source data products make it impossible to guarantee their perfection. For example, the target reliability for sources in unconfused regions of the sky in the 2MASS Catalogs is 99.95% (PSC) and 99% (XSC for |b|>20°). Even at these strict limits, there may be >170,000 unreliable point sources and >12,000 unreliable extended sources. A summary of the types of unreliable sources that are known to have persisted into the Catalogs are given in Sections I.6b.vi and I.6c.

The All-Sky Release PSC and XSC are static, so unreliable sources identified after they are released will not be removed. Catalog sources that are identified to be spurious or contaminated by artifacts will be tabulated in the PSC and XSC Anomaly Lists. These lists will be updated periodically. There are two classes of anomaly lists for the PSC and XSC. The first contains lists of catalog entries that have been confirmed (usually through visual inspection of the images) to be spurious extractions, and not detections of astrophysical sources. The second contains catalog entries that are likely detections of real sources, but that measurements corrupted by confusion, artifacts and/or transient events, and are not so indicated in the cc_flg in the Catalog entries. These lists will be updated periodically as new instances of anomalies are found.

Each entry in the anomaly tables contains basic catalog source identification information and a brief description of the nature of the anomaly. The columns in the table are as follows:

Table 6 - PSC Anomaly List - Spurious Sources

Table 7 - PSC Anomaly List - Contaminated Sources

XSC Anomaly Lists - Please see I.6.c for tables of artifacts, false extended sources and contaminated sources in the XSC.

h. DVD-ROM Release Updates

The 2MASS All-Sky Catalog Tables are available in a bulk distribution on DVD-ROM. These disks do not contain the Image Atlas. Please see I.4 for details.

Updates or corrections to material contained on the DVD distribution set are posted on the All-Sky DVD Release Update web page.

[Last Updated: 2006 Jun 5, by R. Cutri]

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