VI. Analysis of the 2MASS Second Incremental Release Catalogs

1. Comparison of Achieved Performance of Second Incremental Release Catalogs with Level 1 Science Specification

The 2MASS project has prepared a Second Incremental Data Release very similar in characteristics to the First Incremental Release. The Second Release increases the integrated sky coverage in the public domain from 6% to 47%. The 2MASS Second Incremental Data Release contains Image and Catalog data covering 19,681 square degrees of sky, derived from both the North and South observatories. The observations in this Release were obtained between 1997 June 7 and 1999 May 21 UT at Mt. Hopkins, and 1998 March 19 and 1999 February 20 UT at Cerro Tololo. The Second Incremental Data Release products include a Point Source Catalog containing positions and brightness information for over 162 million objects, an Extended Source Catalog containing positions, magnitudes and basic shape information for nearly 600,000 resolved sources, and an Image Atlas containing nearly 1.9 million J, H and K_s images covering the survey area.

The 2MASS Second Incremental Data Release includes an improved processing of data from the area contained in the First Incremental Data Release, and is intended to supercede the earlier release. The improvements in the data processing between the First and Second Incremental Data Releases include the following:

• Correction of a truncation error in the Source Coordinate Designation construction.
• Improved identification of artifacts due to bright bright stars not on the scan being processed.
• Correct handling of singly-detected sources that fall in the overlap regions between tiles.
• Improved identification of observations that are contaminated by residual background structure due to severe atmospheric OH airglow.

The Release homepage supplies the details of sky coverage and source counts. The release documentation will be available as web pages as was the case for the previous release. Section I.6 is of particular interest. It contains a compilation of caveats which will be of interest to users of 2MASS data products. The relevant subsections are:

• General caveats
• Point source notes
• Extended source notes
• Atlas Images notes

Below is a summary of 2MASS Science Team analysis of the Release characteristics in the context of the Survey's Level 1 specifications.

Characteristic	Requirement
Point Source Catalog
a. Photometric Sensitivity	10 at 15.8, 15.1, 14.3 mag for J, H, Ks respectively
b. Photometric Uniformity	<4% bias in photometric zeropoint around the sky
c. Photometric Precision	<5% for bright stars
d. Astrometric Accuracy	<0.5´´ relative to the reference frame
e. Completeness and Reliability	completeness>0.99, reliability>0.9995
f. Bright star photometry	<2% bias for Ks>4.0 mag <5% repeatability for Ks=8.0 mag <10% repeatability for Ks=4.0 mag
Extended Source Catalog
g. Photometric Sensitivity	J<15.0 mag, H<14.2 mag, Ks<13.5 mag
h. Photometric Precision	<10% repeatability for H<13.8 mag
i. Photometric Uniformity	<10% around sky
j. Reliability	>0.80 for |b|>10° >0.99 for |b|>20°
k. Completeness	>0.90 for |b|>30°
General Survey
l. Sky Coverage	>95%
Other Information
m. Seasonal variations

[Last Modified: 2002 Mar 28 by S. Van Dyk.]