I. Introduction
5. Data Release History
Prior to the All-Sky Data Release, the 2MASS project made three releases of Catalogs and Atlas Images drawn from preliminary processing of data made while Survey observations were ongoing. These earlier release products were representative of the data quality of 2MASS, but did not benefit from the full instrumental characterizations or best astrometric and photometric calibration accrued over the life of the Survey. The goal of these releases was to enable access to 2MASS products by the user community as early as possible. Over 1000 papers that made use of these products have already been published, and that number continues to grow.
The 2MASS All-Sky Release products are drawn from a complete reprocessing of all Survey data and are intended to supersede the earlier Release Products.
A summary of all 2MASS data releases follows in chronological order. More information regarding each of these release can be obtained by clicking on the links in each subsection.
a. The 2MASS Sampler (December 1998)
The 2MASS Sampler was the first release of 2MASS data products, and was designed to introduce the community to the contents and formats of 2MASS data products. The Sampler Release was drawn from Survey observations made on one night at the northern observatory, 16 November 1997 UT. The release products included a Point Source Catalog containing photometry and positions for 227,197 objects, an Extended Source Catalog containing 2133 resolved sources, and an Image Atlas containing 5,658 FITS images.
b. The 2MASS First Incremental Data Release (May 1999)
The 2MASS First Incremental Data Release (IDR1) contained data from approximately 2483 deg2 of northern sky (6% of the full sky) observed during the first six months of the Survey. IDR1 included a Point Source Catalog containing data for 20,204,378 sources, an Extended Source Catalog containing positions, magnitudes and basic shape information for 73,980 resolved sources, and an Image Atlas containing 233,979 J, H and Ks FITS images.
c. The 2MASS Second Incremental Data Release (March 2000)
The Second Incremental Data Release (IDR2) contained data covering 19,681 deg2 (48%) of sky, derived from observations made at both the northern and southern 2MASS facilities. The IDR2 included a PSC containing photometry and astrometry for 162,213,354 sources, an XSC containing 585,056 resolved sources, and an Image Atlas containing 1,897,500 J, H and Ks FITS images.
d. The 2MASS All-Sky Data Release (2003 March 25)
The 2MASS All-Sky Data Release contains Atlas Image and Catalog data covering 41,252.255 deg2 (99.998%) of the sky, drawn from all Survey observations. The All-Sky Release PSC contains photometry and astrometry for 470,992,970 sources. The All-Sky Release XSC contains photometry, positions and basic shape information for 1,647,599 sources found to be resolved relative to a single point-spread-function. The Image Atlas for the All-Sky Release contains 4,121,439 J, H and Ks calibrated FITS images covering the full sky.
e. The 2MASS Extended Mission Data Release (2006 December 20)
The 2MASS Extended Mission Data Release contains Atlas Images and extracted source Databases drawn from survey, calibration and special long exposure ("6x") observations made at the 2MASS facilities between June 1997 and January 2001 that were not incorporated in the All-Sky Data Release. These ancillary products complement the highly uniform and reliable All-Sky Release Catalogs and Atlas by providing multi-epoch images and measurements of objects observed multiple times during the survey, and measurements of sources fainter than may be found in the primary survey Catalogs. The fainter flux limits and extended time coverage are obtained at the expense of reliability and uniform sky coverage. The Extended Mission Images and Databases are intended to be used as a resource to learn more about individual objects where detailed follow-up is possible, or to conduct studies of fainter objects over small regions of the sky that do not require the high degrees of uniformity and reliability that characterize the All-Sky Catalogs.
[Last Update: 2007 July 13; R. Cutri]
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