- B. Light:
presented the comparisons that he and S. Wheelock have been doing
for R2 vs. R2-R1 positions coming out of KAMPHOT and FREXAS.
He showed an offset in inscan positional difference, delta y, for
bright stars in ascending vs. descending scans in the FS28 scan; the average
positional difference between these is about 0.2 camera pixels. There is
also an offset from zero for both ascending and descending positions.
This offset has been known about for a long time and is accounted for in
the pipeline. It is thought to be due to shifting of the secondary affecting
the R1 more than the R2 data; the effect is not a software issue since the
same results are found from FREXAS and KAMPHOT.
Bob then demonstrated that the offset varies in size from one scan to another.
He has found no dependence of the size of the offset with airmass, but
speculated that there may be a possible dependence on temperature. A
similar, though smaller, effect is seen between ascending vs. descending
scans in cross-scan pixel position differences, delta x: about 0.1 camera
pixels.
- S. Charnoz:
briefly reported that he is working to match Tycho stars with
2MASS. He has determined the number and distribution of Tycho
stars in each scan. There are about a dozen scans with only 1 Tycho star,
and a significant number with <5. The median number of Tycho stars per scan
is about 18, with a maximum of >100 for scans through the Galactic Plane.
Statistics were obtained on the distribution of stars within each scan, such
as the mean gap between Tycho stars, the size of the gap at the ends of each
scan, the largest gap within each scan, etc. H. McCallon will use these
results to determine the accuracy of the pointing reconstruction using the
new method. More details will follow.
- S. Wheelock:
has also been working with Tycho stars - tracking them all the way
back to frame coordinates in some Coma fields to aid with tests
of POSMAN.