Background anomalies from internal reflections in the camera contribute to background problems around very bright stars in the coadded images. Internal reflections cause differences in the shape of the background surrounding very bright stars, in turn causing background discontinuites in the coadded images that cannot be fixed by adjusting each frame by a constant. The current processing can be improved, but the problem probably will not be completely solved.
The following images show for each band 6 succesive flattened frames as the southern camera transits Betelguese. The stretch range is 3000 dn in these images, with white being the lowest, the red/green transition at about +1000 dn, and the greeen blue transition at about +2000 dn.
J Band
H Band
Ks Band
J Band
Tests have been performed dropping all, and part of, the frames containing a very bright star (Beta Peg in 971116n/s027). In the images below, the first shows the coadd in each band with all the data, none of the data from frames containing Beta Peg, and then none of the frames containing Beta Peg except for the middle portion of the frame centered on Beta Peg.
H Band
Ks Band
The small holes are caused by dead pixels, and the larger square holes are due to solo blanking (in these coadds, false solos caused by a problem in the current pipeline algorithms identifying solos).
An untested possible improvement is to use all 6 frames for the 3 panels centered on the bright star (Beta Peg in this case).
This page last updated on Feb 14, 2001.
Gene Kopan - gene at ipac.caltech.edu