SEEING
The obvious problem with constructing 3-channel data from
3 separate individual scans is that the seeing and
photometric conditions are different for each band; thus,
there are problems unique to this data set that should
not come into play for real 3-channel data. An additional
problem is te registration itself. The pixel scale for the
three bands are slightly different, so there is a relative
distortion between the bands. Again, this problem is unique
to this data set and should not be a problem for the real
3-channel data.
The SA57 scans were taken on the night of 95-04-24,
which was classified as a "photometric night". But, below we
provide the "seeing" track for a few of the SA57 scans,
which show that the seeing was rather dreadful for the
J and H scans, and not so bad for the K scans. Based on the
seeing results, particularly H, it is a good bet that
the scans were not taken under anything resembling a
"photometric" condition. Nevertheless, the data set does
provide an excellent medium to test the GALWORKS modules and
design features. (Additional caveats are given as
appropriate in the following
sections.)
The following figures show the seeing for scans 039 and
042. The seeing is represented by the "shape" parameter,
which is a combination of two parameters describing the
stellar profile:
f = f0 * exp [- (r / alpha) ** (1/beta) ]
where f0 is the peak flux, r is the radial distance from the
peak center, alpha and beta are the scaling parameters.
The shape
is defined to be (alpha * beta).
The figures represent shape versus scan coordinate. Two versions are
included: The first is the "seeman" version, or the
seeing values computed by the SEEMAN module (for additional
details see the SEEMAN SDS); The second is the GALWORKS version,
"seeridge" which uses the same information as the SEEMAN version
but computes the seeing with a slightly more sources
per seeing value (and thus is a more accurate measure of the
seeing, assuming that the seeing is tracked during the
duration of time comprising the set of sources per seeing value).
For good seeing, (FWHM < 2"), the shape value is less than
1.1 or so. Very bad seeing corresponds to shape values > 1.2
or so. Notice that the seeing is terrible for H band, but
pretty good (around 2" FWHM) for K band.
