VI. Analysis of the 2MASS Second Incremental Release Catalogs
7. Comparison to External Catalogs and Models
c. 2MASS Calibration Star Photometry in the Second Incremental Data Release Point Source Catalog
The global 
2 minimization procedure by
M. Weinberg and S. Nikolaev,
described here
has produced photometry of stars in the 2MASS Calibration Fields with exquisite
internal uniformity and self-consistency. The internally consistent
photometry of the secondary standard stars developed from this procedure
are used for nightly 2MASS photometric calibration.
The primary and secondary standard stars that are observed during
normal survey scans are calibrated using the nightly photometric
solutions, and these calibrated magnitudes are reported in the
Point Source Catalog. We can examine the difference between the
photometry reported in the PSC and the "best" magnitudes for those stars
from the global 2 minimization procedure
to measure the internal consistency of photometry
reported in the PSC and the 2MASS natural photometric system.
Of the 1036 primary and secondary 2MASS calibration stars, 470 are included in the PSC for the Secondary Incremental Data Release. Figure 1 shows the sky coverage map for the upcoming release, and marked in green the positions of the calibration stars found in the PSC. Shown in red are the positions of calibrators not found in the PSC. All calibrators that are in the coverage area of the release are in the PSC.
|
| Figure 1 |
In Figures 2, 3, and 4 the difference between the "truth" photometry and the PSC photometry for each calibration star is plotted against the true magnitude. The right side of each figure provides a histogram of the photometric residuals.
The mean and RMS photometric residuals in each band are shown in the three plots. The RMS residual in all bands is ~0.03 mag. No significant bias between the the PSC and "truth" photometry is seen.
There are a couple of stars that show relatively large (>0.1 mag) discrepencies between the PSC and truth photometry. J. Gizis has begun an investigation into these measurements; the results can be seen here.
|
|
|
| Figure 2 | Figure 3 | Figure 4 |
[Last Updated: 2000 February 9 by R. Cutri. Modified 2000 Aug 29 by S. Van Dyk.]
Previous page. Next page.
Return to Explanatory Supplement TOC Page.