- L. Fullmer:
showed the results of her analysis of
the bogus galaxy extractions near bright stars; in a plot of radial
distance of the bogus `galaxy' vs. magnitude of the bright star there
is an upper envelope, as might be expected, showing that the `bogeys'
are found systematically nearer to fainter stars. Most `bogeys' were
found in the J band. This envelope can now be used to revise the
bright star mask used by GALWORKS; it will have to extend out to 12th
magnitude at J. A few very bright stars were found not to be on the
GALWORKS mask list for some reason; T. Jarrett will investigate.
- T. Chester:
gave an update on his and T.
Jarrett's efforts to investigate the possibility of tracking seeing
within a scan. Using a running average of the GALWORKS shape parameter
over 10 to 14 stars with a 5 star overlap, they showed very promising
seeing timelines for several scans. There are some small intervals
where the seeing appears to blow up and the algorithm, which currently
is a simple running average with a few sigma rejection of the highest
and lowest points, drops out. The biggest problem with tracking seeing
through such intervals is the need to do the upper envelope 2.5 sigma
rejection in order to avoid the risk of including extended objects
(galaxies) in the seeing estimate. It may be a better idea to use the
lower envelope of the data, instead of the running average, to avoid
this problem. Tom Chester plans next to determine the effect of the
kinds of seeing flare ups he and Tom Jarrett are finding on the
photometry and reliability of galaxy detection, as well as on the point
source photometry.
- R. Cutri:
discussed the latest results of his
and S. Wheelock's analysis of the photometric zero points for the 1995
data. The resulting absolute photometric uncertainties are in the 1.5
to 4% range, which is uncomfortably high. There are several possible
reasons for the lack of precision in the measurements. First is the
possibility of real zero point variation during the night, due perhaps
to dust settling out of the atmosphere. The number of standard stars
observed during most nights of the 1995 run was too small to track such
behavior. Second is the suspicion that some of the standards have
systematic offsets; we are still awaiting information from the UKIRT
staff about this possibilty. Third is the possibility that significant
color terms need to be taken into account. Another possibility is
untracked seeing variation during each of the scans. Overall, the
results definitely point to the need for more and better standard star
observations during survey operations.
- G. Laughlin:
gave a brief status report on her
study of the reliability of GALWORKS galaxy extractions using FOCAS on
a Coma coadd field. She and R. Cutri have taken the process through
identification and are now learning how to tune the FOCAS parameters to
maximise reliability of the galaxy extractions; their first effort
produced far too many `sources'. The next step is to try subtracting a
uniform background before source identification.
- C. Lonsdale:
reported that she had observed 2
extremely red 2MASS objects at the Palomar 200 inch telescope on Sept.
29. These 2 objects were among 6 that D. Kirkpatrick found in the
92-94 database with red J-K color and R-K in the 3-4 range: candidate
new QSOs.