2MASS V3 Production Processing

Read1 Source Quality Assesment

Summary

The following table summarizes the rd_flg breakdown for catalog sources with at least one band of rd_flg 1 or 3. 

        30752 (99.54%)  3 band sources R1 saturated in at least one band 
	  119           2 band sources R1 saturated in at least one band
	   11           1 band sources R1 saturated
	   13           R1 sources known to be missing 
      2259768 (98.37%)  3 band sources R1 total 
	21831           2 band sources R1 unsaturated in at least one band
	15542           1 band sources R1 unsaturated in at least one band
A detailed histogram by rd_flg is here.

The majority of single band R1 sources are fainter than the (R2-R1) saturation threshold, and are present only due to the fact that the corresponding (R2-R1) measurement was marked as an artifact and discarded. The R1 measurement was not so discarded due to inconsistencies in artifact flagging for the read types. The bulk of the remaining brighter single band R1 sources are remnants of inconsistent resolution of confused sources.

The majority of the 2 band R3 sources are missing Ks band due to a noisey column in the Northern Ks array that had to be masked off in the processing. The remainder of the R3 sources missing bands are due to confusion problems.

Photometry

  • R1 Overall Photometry meets or exceeds catalog requirements.

    Special Photometric Issues

    A number of R1 sources have special flag values for the photometric sigmas (?_msig). The R1 photometric sigmas are discussed here.

    The saturated R1 (R3) sources were not corrected for seeing in the catalog due to inability to complete the calibration in time for the catalog release. These errors cause calibration errors and biases of 0.2-0.4 magnitudes for many of the saturated R1 sources.

    Astrometry

    The astrometry of the R1 sources (~100 mas) easily meets the requirement (500 mas), even for the saturated R1's (~170 mas). The astrometry of the R1 sources is somewhat less accurate than the bright (R2-R1) sources due to correlated errors between the 3 bands. This correlation was not accounted for during band merging, resulting in underestimation of the R1 uncertainties. Also, due to an oversight, the frame distortions (up to 0.2" at frame edge) were not corrected for in the R1 position reconstruction. The astrometry of the saturated R1's (R3's) is somewhat worse due to asymmetries in the saturated profiles and a deficit of information when a small number of pixels are saturated.

    Completeness

    A search for Tycho stars in the catalog revealed close to 100% completeness in the R1 measurements of Tycho sources. Details of the Tycho completeness check may be found here.

    A small number of bright sources were marked as artifacts and thus omitted from the catalog. Thirteen of these are listed here.

    There are also a number of close doubles where 1 member is missing, or measurements are missing in one or more bands due to confusion problems. The radial profile technique used for measuring saturated R1 stars was not well suited for separating doubles, and time was not available to develop methods for deblending bright stars.

    This page last updated on Dec 3, 2002.

    Gene Kopan - gene at ipac.caltech.edu