The Two Micron All Sky Survey at IPAC

J/H/Ks color composite of the 2MASS Combined Calibration Scan Image in rho Ophiuchus

This is the release of Ancillary Data Products from the Two Micron All Sky Survey (2MASS) Extended Mission. The Ancillary Products are drawn from survey, calibration and special long exposure observations made at the 2MASS facilities at Mt. Hopkins, AZ and Cerro Tololo, Chile between June 1997 and January 2001. They are intended to complement the highly uniform and reliable All-Sky Release Point and Extended Source Catalogs and Image 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 2MASS Extended Mission Ancillary Products do not replace the All-Sky Release Catalogs and Atlas. Rather they 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. The fainter flux limits and time sampling in the 2MASS Extended Mission Ancillary Data products are obtained at the expense of reliability and uniform sky coverage. Furthermore, the Extended Mission products have not received the same level of validation and scrutiny as the All-Sky Release products. Consequently, users should defer to the source data contained in the 2MASS All-Sky Catalogs, whenever possible.

Users are encouraged to familiarize themselves with the Explanatory Supplement to the 2MASS All Sky Data Release and Extended Mission Products before using any 2MASS image, catalog, or database. Please review the Cautionary Notes sections pertaining to each Ancillary Product to learn about the limitations of the Extended Mission data.

The Extended Mission Ancillary Products are (click on product name to go to a description):

1. Survey Point and Extended Source "Reject" Tables and Full Survey Image Atlas
2. 6x Point and Extended Source Working Databases and Catalogs and 6x Image Atlas
3. Calibration Scan Point and Extended Source Working Databases and Calibration Image Atlas
4. Survey, 6x and Calibration Merged Point and Extended Source Information and Cross-Reference Tables
5. Combined Calibration Scan Image and Source Lists

Access the Database and Image data via the NASA/IPAC Infrared Science Archive (IRSA)	View the on-line 2MASS Explanatory Supplement
Consult frequently asked 2MASS questions (FAQs)	Email the 2MASS Help Desk for user support or more information

I. Survey Point and Extended Source "Reject" Tables and Full Survey Image Atlas

• Tables containing positions and fluxes for 843,988,897 point source and 943,441 extended source detections extracted from all 2MASS survey observations made in photometric conditions that are not contained in the 2MASS All-Sky PSC and XSC. The "Reject" Tables include:
  1. One or more independent measurements of objects in the ~30% of the sky observed more than once during 2MASS survey-mode observations to supplement the single apparitions selected for the All-Sky PSC and XSC
  2. Low-SNR sources below the All-Sky Catalog thresholds for reliability which are a mixture of faint objects and noise excursions
  3. Spurious detections of image artifacts and transient events such as cosmic rays and residual meteor trails.
• 4,879,128 photometrically and astrometrically calibrated FITS images in the three 2MASS bandpasses constructed from all survey mode observations. These include the 4,121,439 images released as part All-Sky Release Image Atlas, and 757,689 images from repeated observations of selected regions.

Figure 1 - 2MASS survey depth-of-coverage map, galactic aitoff projection, showing Tile overlap regions and full Tiles observed multiple times.	Figure 2 - Cumulative area of sky plotted as a function of number of independent survey observations from repeated Tile scans.	Figure 3 - (left) Light curves of a candidate pre-main sequence star in the Orion Molecular Cloud, and (right) its evolution in the color-color and color-magnitude plane (Carpenter et al. 2001) constructed from 28 independent survey scans of the region.

II. 6x Point and Extended Source Working Databases and Catalogs and 6x Image Atlas

• 24,023,702 point and 247,091 extended sources extracted from a set of special observations made at the end of 2MASS survey operations that used exposure times six times (6x) longer than the main 2MASS survey measurements. These measurements reached ~1 mag deeper than the main 2MASS survey, and covered approximately 590 deg² of sky in 30 regions containing targets of interest including star formation regions, the Pleiades, nearby galaxies and galaxy clusters, the Lockman Hole and the Large and Small Magellanic Clouds.

  The 6x point and extended source tables are released as integrated Catalog/Working Databases. The Working Databases may contain more than one independent detection of objects scanned multiple times, and a significant number of unreliable extractions of noise and image artifacts. The 6x Point and Extended Source Catalogs (denoted by cat=1) are a uniform and reliable subset of objects in 6x Point and Extended Source Working Databases. These Catalogs are appropriate for use in statistical studies analogous to the All-Sky PSC and XSC, but over the limited areas covered by the 6x observations.

• 69,687 photometrically and astrometrically calibrated FITS images in the three 2MASS bandpasses constructed from the long exposure observations of all fields.

Figure 4 - J/H/Ks color composite showing a 0.9°x0.7° region in the core of the Abell 426 (Perseus) galaxy cluster 6x field.	Figure 5 - J/H/Ks color composite showing a 0.5°x0.4° region in the core of the IC348 star formation region 6x field.
Figure 6 - Comparison of 6x and All-Sky PSC and XSC differential source counts in the 28.3 deg2 6x Lockman Hole field. Counts are and scaled by area.	Figure 7 - Click on this image to view a blink comparison between the color-magnitude diagrams from the 2MASS 6x-PSC and All-Sky Release PSC for objects in the 5.3 deg2 Pleiades 6x field.

III. Calibration Scan Point and Extended Source Working Databases and Calibration Image Atlas

• 191,464,020 point source and 403,811 extended source detections extracted from observations of the 35 8.5´×1° calibration fields that were measured nightly during 2MASS survey operations. Each field was scanned between 562 and 3692 times over the 3.5-year duration of the survey, so the Calibration Working Databases are highly redundant, multi-epoch data sets.
• 878,769 photometrically and calibration FITS images in the three survey bandpasses constructed from all 2MASS survey calibration-mode observations.
• 5,041,472 point source and 9,709 extended source detections extracted from observations of 5 special 8.5´×1° calibration fields in and around the LMC and SMC. These fields were scanned between 108 and 468 times in support of the long exposure (6x) observations of those fields. The special calibration fields were observed with the same exposure times and scanning strategy as the main survey calibration fields.

• 18,504 photometrically and calibration FITS images in the three survey bandpasses constructed from the special LMC/SMC calibration field observations.

Figure 8 - Phase-folded J and Ks light curves and magnitude-color behavior constructed using the 2977 independent measurements of an RR Lyr variable in the 90004 calibration field (courtesy A. Becker).	Figure 9 - Position of LHS 191 as a function of time from the 1839 independent observations of the 2MASS 90191 calibration field, showing the proper motion (1.022 arcsec/yr) and parallax (0.056 arcsec) of the nearby M-dwarf star. Cyan points are positions from individual calibration scans, and black points are average positions from six scans in each calibration field observation.

In addition to the primary extracted source databases and calibrated image products from the main survey, long exposure (6x) and calibration observations, the 2MASS Ancillary Products include two "value-added" products that are designed to assist users in exploiting the multi-epoch 2MASS observations:

IV. Survey, 6x and Calibration Merged Point and Extended Source Information and Cross-Reference Tables

• Tables containing the combined position and brightness information for point and extended sources detected more than once in each of the 2MASS survey, long exposure (6x) and calibration data sets, along with assorted statistics on flux and position distributions for each merged object. These tables, used in conjunction with the respective Catalogs and Working Databases, provide the best available estimate of flux and position from 2MASS for sources that benefited from more than one observation during the survey.
• The Cross-Reference tables provided for the Merged Survey, Long-Exposure (6x) and Calibration Tables link each merged source entry with the individual epoch measurements in the respective extracted source Working Databases.

Figure 10 - Click on this image to view a blink comparison between the color-magnitude and two-color Hess diagrams for sources in the 2MASS Survey Merged Point Source Information Tables and the All-Sky Release PSC within 20° of the north galactic pole. Note the improved definition of the main stellar population features for faint sources in the Merged Point Source color-magnitude diagram.	Figure 11 - Color-magnitude diagram from the 2MASS PSC (left) and Calibration Merged Point Source Information table (right) for objects in the 90067 calibration field detected more than 1000 times. Note the clear delineation of the main sequence and binary main sequence in the Merged Calibration color-magnitude diagram.

V. Combined Calibration Scan Image and Source Lists

• A set of photometrically and astrometrically calibrated FITS images constructed by optimally combining the 562-3692 independent observations of each of the 35 2MASS Calibration fields acquired during Survey operations. The images reach 3.5-4.5 magnitudes deeper than the single epoch measurements and cover a total area of approximately 6 deg².

• A table of 246,760 sources detected in each of the deep, Combined Calibration Scan FITS Images is also provided. These provisional source extractions have simple aperture photometric measurements bootstrapped to the brightness of the standard stars in each Calibration field, and are useful for comparing with the results of independent extractions by users of the data.

Figure 12 - Click on this image to view a comparison between images from a single epoch 2MASS calibration observation of the 90004 Calibration field, and the Combined Calibration image constructed using 1400 independent observations of the field.	Figure 13 - Click on this image to view a comparison between a deep 2MASS Combined Calibration image and SDSS image in the 90004 calibration field illustrating their complementary depth.

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