I. Introduction

8. Referencing 2MASS

a. 2MASS Source Naming Convention

Source designations for objects in 2MASS Catalogs conform to the recommendations outlined in International Astronomical Union's Specifications concerning designations for astronomical radiation sources outside the solar system. Source designations should be given as:

2MASxy Jhhmmss[.]s±ddmmss

The brackets and period are not explicitly in the name, and are shown above only to illustrate that the last digit before the declination sign is tenths of RA seconds. The tenths digit is truncated rather than rounded, per the IAU recommendation. The x and y in the acronym correspond to characters that specify the catalog and data release from which the object was taken, respectively. The acronyms are as follows:

2MASSsFor objects in the 2MASS Sampler Point Source Catalog
2MASXsFor objects in the 2MASS Sampler Extended Source Catalog
2MASSIFor objects in the Incremental Release Point Source Catalogs (this release)
2MASXIFor objects in the Incremental Release Extended Source Catalogs (this release)
2MASSWFor objects in the Working Point Source Databases (pre-release)
2MASXWFor objects in the Working Extended Source Databases (pre-release)

The coordinate sequence is the sexigesimal J2000-equinox RA and declination, hence the "J" designator.

The acronym designation is not carried explicitly for entries in the Catalogs to minimize duplication. The proper designation for objects in the this and all following Incremental Data Releases is 2MASSI and 2MASXI. The coordinate sequence is tabulated for each source and is included in the source record entry in the Catalogs.

Source Designation Error in the 2MASS Spring 1999 Release Catalogs

A small fraction of sources in the 2MASS Spring 1999 Point and Extended Source Catalogs (~0.08%) suffered from a rounding/truncation error in the coordinate name generation algorithm that resulted in time decisecond values of "600" or arcsecond values of "60." The erroneous values exist only in the source designation; the J2000 right ascension and declination supplied for the sources are correct.

The following tables provide the J2000 positions of source in the 2MASS Spring 1999 Point and Extended Source Catalogs that have incorrect name designations. For each source, the incorrect designation is given, followed by the corrected name.

Corrected Point Source Catalog Designations

Corrected Extended Source Catalog Designations

[Last Update: 1999 October 5, by R. Cutri]

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