I. Introduction

3. Executive Summary of 2MASS First Incremental Data Products

a. Point Source Catalog (PSC)

The 2MASS First Release PSC contains astrometry and photometry in the three survey bandpasses for 20,204,378 sources that were detected in the survey image data. Positions, magnitudes, astrometric and photometric uncertainties, associations with ACT or USNOA optical catalog sources and a number of flags indicating the quality of the photometry are presented for each source.

The PSC also contains point-source processed photometry for virtually all of the resolved sources found in the Extended Source Catalogs.

b. Extended Source Catalog (XSC)

The 2MASS First Release XSC contains positions and photometry in the three survey bandpasses for 73,980 objects found to be resolved relative to a single point-spread-function during processing. Positions, magnitudes measured in a wide variety of ways, uncertainties, associations with several external catalogs and a number of flags and scores indicating the quality of the measurements, and the likelihood of "extendedness" are presented for each source.

c. Image Products

i. Atlas Images

The 2MASS First Incremental Data Release includes 233,979 FITS images in the three survey bands constructed from the scans of 8.5' × 6° long Survey Tiles. 223,806 of the images are 512×1024 (1"/pix) in size, and a small number, 10,173, from the ends of scans are 512×698 (1"/pixel). The J, H and Ks 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.

Because of the prohibitive size of image data, currently only ~20:1 lossy-compressed versions of the Atlas Images are accessible on-line. Compression of the images was carried out using the hcompress procedure. It is hoped that it will be possible to serve the full resolution Atlas Images in the future.

ii. Extended Source Postage Stamp Images

Small cut-outs of the full resolution J, H and Ks Atlas Images around each of the XSC sources in the First Incremental Data Release are available on-line. The image sizes are scaled to the size of the object, ranging from 21´´ × 21´´ for the faintest galaxies (Ks > 13 mag) to the maximum 101´´ × 101´´ for the largest galaxies that 2MASS can always fully image in a single Tile. For galaxies larger than 101´´, it is best to use the 2MASS Survey Visualizer, which will display larger (but lossy compressed) 2MASS Atlas images.

The 2MASS Extended Source Images are 3-dimensional FITS image cubes. Each cube contains three image planes, and each plane contains the J, H and Ks 2MASS image data, respectively. The near-infrared background emission has been subtracted from each image plane. Positional and photometric calibration information are included in the image header.

[Last Updated: 1999 May 6; by R. Cutri]

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