II. Contents of the Second 2MASS Incremental Data Release

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4. Atlas Images

The 2MASS Second Incremental Data release includes 1,897,017 FITS images in the three survey bands constructed from the scans of 8.5´ × 6° long Survey Tiles. The image data from each Tile are divided into twenty-three separate Atlas Images in each band. Twenty-two of these are 512×1024 (1"/pix) in size, and one is 512×698 (1"/pixel). Thus, there are 1,814,538 512×1024 images and 82,479, 512×698 Atlas Images in the Release. The J, H and K_s images for each region of sky are resampled to the same scale and registered to facilitate 3-color investigations. Positional and photometric calibration data are carried in the FITS header for each image.

A ~20:1 lossy-compressed version of the Atlas Images, known as the "Quicklook" Images, are also available. These images are suitable for position measurements, finding charts and visual inspection of the near-infrared sky. However, they should not be used for quantitative photometric measurements because of the information lost during the compression process. Compression of the images was carried out using the hcompress procedure.

Both the Atlas Images and Quicklook Images are accessible on-line.

[Last Updated: 2001 January 31, by R. Cutri]

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