IV. 2MASS Data Processing

4. Point Source Detection and Photometry

e. The Default Magnitude

The origin of the "default magnitude" specified in the records for each object in the 2MASS PSC is described by the "rd_flg" values for each band. For most objects, the default magnitude is the profile-fit magnitude from the 1.3-sec (R2-R1) exposures, and the corresponding "rd_flg" value for the profile-fit photometry is "2" in the appropriate band. The curve-of-growth-corrected "standard aperture" (4´´ radius) magnitudes (j_m_stdap, h_m_stdap and k_m_stdap) and uncertainties are also provided for most objects in the Point Source Catalog. On occasion, the profile-fitting photometry for a source will fail to converge, and no valid point-source photometry will be produced. If there exists a curve-of-growth-corrected aperture magnitude for such objects, this magnitude will be listed in the "default magnitude" entry, and the "rd_flg" for the appropriate band will have a value of "4." Extreme caution should be used in interpreting these magnitudes because they sources are usually found in confused regions where there is often serious contamination in the sky annuli for the aperture measurements.

If a source is saturated in the 1.3-sec exposures, but not in the 51-msec (R1) exposures, then the default magnitude specified in the appropriate band is taken from the aperture photometry from the R1 frames. The corresponding "rd_flg" value in this case is "1". If the source is saturated in even the 51-msec R1 exposure in a band, then the default magnitude is listed as "-99.999" and the "rd_flg" value is "3".

[Last Updated: 2000 June 20; by R. Cutri]

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