Appendix 1. Introduction to the 2MASS Extended Mission and Ancillary Data Products
5. 2MASS Source Naming Convention
Sexagesimal source designations are not carried explicitly in the Survey Reject Tables, 6x Working Databases and Catalogs, or the Calibration Working Database tables as they are in the All-Sky Release Point and Extended Source Catalogs.
Because there may be multiple detections of the same object in each of the extracted source databases, the position-based sexagesimal designation may not be a unique object identifier. To avoid confusion, we recommend that sources be refered to by their designation in the 2MASS All-Sky PSC or XSC, whenever available.
If users wish to refer to a Survey Reject Table, 6x and Calibration Working Database or 6x Catalog entry that does not have a corresponding entry in the All-Sky Catalogs using a sexagesimal notation, the designation should be formed from the decimal equatorial coordinates following the convention used for the All-Sky and Incremental Release Catalogs (I.8.a). This convention conforms to the recommendations outlined in the International Astronomical Union's specifications concerning designations for astronomical radiation sources outside the solar system.
Source designations should be given as:
2MASxyz Jhhmmss[.]ss±ddmmss[.]s
The brackets and periods are not explicitly in the name, and are shown above only to illustrate that the last digits before the declination sign are tenths and hundredths of RA seconds and the final digit in the designation is in tenths of DEC arcseconds. The decimal parts are truncated rather than rounded, per the IAU recommendation. The coordinate sequence is the sexagesimal J2000-equinox RA and declination, hence the "J" designator.
CAUTION: Coordinates extracted from the designation column in the All-Sky Catalogs are less accurate than those given in the right ascension and declination columns. The use of designation coordinates will result in a maximum (unsigned) error of 0.0996" in declination and a maximum (unsigned degree) error of 0.1488" in right ascension.
The x, y and z in the acronym
correspond to characters that
specify the Catalog/Reject Table/Database and data set from
which the object was taken, respectively. The acronyms are as follows:
| Acronym | Catalog/Database |
| All-Sky and Incremental Release Tables | |
| 2MASS | For objects in the All-Sky Point Source Catalog |
| 2MASX | For objects in the All-Sky Extended Source Catalog |
| 2MASSI | For objects in the Incremental Release Point Source Catalogs |
| 2MASXI | For objects in the Incremental Release Extended Source Catalogs |
| 2MASSs | For objects in the 2MASS Sampler Point Source Catalog |
| 2MASXs | For objects in the 2MASS Sampler Extended Source Catalog |
| 2MASSW | For objects in the Survey Pre-Release Point Source Working Databasea |
| 2MASXW | For objects in the Survey Pre-Release Extended Source Working Databasea |
| Extended Mission Release Tables | |
| 2MASSA | For objects in the Survey Point Source Reject Table |
| 2MASXA | For objects in the Survey Extended Source Reject Table |
| 2MASSm | For objects in the Survey Merged Point Source Information Table |
| 2MASXm | For objects in the Survey Merged Extended Source Information Table |
| 2MAS6W | For objects in the Long Exposure (6x) Working Point Source Database |
| 2MASX6W | For objects in the Long Exposure (6x) Working Extended Source Database |
| 2MAS6m | For objects in the Long Exposure (6x) Merged Point Source Information Table |
| 2MASX6m | For objects in the Long Exposure (6x) Merged Extended Source Information Table |
| 2MASCW | For objects in the Calibration Scan Working Point Source Database |
| 2MASXCW | For objects in the Calibration Scan Working Extended Source Database |
| 2MASCm | For objects in the Calibration Scan Merged Point Source Information Table |
| 2MASXCm | For objects in the Calibration Scan Merged Extended Source Information Table |
| 2MASCd | For objects in the Combined Calibration Image Extracted Source Lists |
Notes to Table 1:
a - The Pre-Release Survey Point and
Extended Source Working Databases (2MASSW, 2MASXW) refer to the datasets
generated from the first, preliminary processing of the Survey data conducted
while Survey operations were ongoing. The 2MASS Sampler, First and Second
Incremental Data Releases were drawn from these Databases.
Example:
The complete designations for two sources in the 2MASS Survey Point and Extended Source Reject Tables and their cross-identifications in the 2MASS All-Sky PSC and XSC are:
2MASSA J18365633+3847012
(= 2MASS J18365633+3847012 = 
Lyr)
and
2MASXA J13245247+1404382 (= 2MASX J13245247+1404382 = NGC 5137).
[Last Update: 2006 September 29, by R. Cutri]
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