Cloudy Scans in the 2MASS Final Release
000218n scan 014
The J, H and Ks backgrounds for this north-going scan show the signature of moonlit clouds between frames 20 and 50 and again between frames 170 and 220. To assess the extent to which photometry is compromised, we selected detections from this scan meeting the following criteria in the v3 working point source database -
((j_snr > 10.0) and (h_snr > 10.0) and (k_snr > 10.0)) and cc_flg = '000'
then paired those up (using a 2-arcsecond radius) with other cc_flg = '000' sources in scans that overlapped this one. Plots of the delta magnitude for sources on a scan-by-scan basis are shown in the following plots:
Notice that all plots show the same behavior. Any photometric problem caused by the first incursion of clouds in frames 20-50 is not evident in any of these plots. However, the second incursion - between frames 170 and 220 - shows up as a slow wander away from delta(mag)=0 in all bands and in all plots. A concatenation of all overlaps onto one plot shows this more clearly. At its most opaque (near Dec = 82.4 degrees) the cloud has caused average dimmings of
All objects between 81.5 deg < Dec < 83.2 deg will be dimmed by amounts less than or equal to these maximum values.
000728s scan 049
The J, H and Ks backgrounds for this south-going scan show the signature of a cloud appearing suddenly around frame 242. We selected point source detections from this scan as discussed in the section above and produced the following scan-by-scan overlap plots:
Again, all plots show the same behavior. No photometric offsets are see at the north end of the scan, but large offsets are seen with every scan overlapping this one at the south end. A concatenation of all overlaps onto one plot shows this more clearly. The cloud affects the photometry for sources with 5.99 < Dec < 6.6 deg and causes maximum dimmings of
