- G. Laughlin:
reported that she is making steady
progress on learning FOCAS and applying it to 2MASS images in order to
check the reliability of GALWORKS extractions. The first problem she
came across was how to make FOCAS work on an image as large as a 2MASS
coadd.
- C. Beichman:
gave a status report on the
confirm/bandmerge processing for the May 1995 data. The details of the
approach are somewhat different from the ultimate pipeline design
because (a) the 3 band data were not obtained simultaneously, and (b)
there is more than one coverage in some bands in some regions; however
the basic techniques will be similar. The first step is to find all
scans within a band that cover a position, then to derive an average
position and magnitude. For multiple sightings, sigma_pop was used as
the resulting positional uncertainty, and 1 arcsec was adopted as a
default positional uncertainty for single sightings.
Chas described the optimization process he has been analyzing, which
involves comparing the false match rate to the `bust-up' rate as a
function of the bandmerge radius. The false match rate is derived from
the number of sources having with N+1 reported sightings, where N is
the number of coverages, and the `bust-up' rate is found from the
increase in the number of sightings per source as the match radius
decreases. These two effects are a function of the background source
density. A compromise between these two effects results in an optimum
confirmation radius of about 1.5 arcsec.
- D. Kirkpatrick:
summarized the results of the
efforts he and C. Beichman have made to confirm and bandmerge all the
sources resulting from pre-1995 prototype camera runs. Their results
are summarised in a memo about to be released to the science team.
There are about 1.2 million sources in the cleaned up database, about
10% of which are 3-band sources. Most band gaps are due to lack of
coverage. T. Evans matched the database to the APM catalog, therefore
it includes B and R magnitudes for many sources. The database covers
about 0.5% of the sky and will shortly be available to the science team
in xcatscan.
- L. Fullmer:
gave a status report on her work to
locate bogus sources generated near bright stars, which she is doing
for the purpose of tuning the bright star mask. She is finding some
bogus sources around stars which are fainter than the current mask
limit, therefore it seems that the bright star mask will have to be
extended to a fainter limit.
- S. Terebey:
reported that the tuning of GALWORKS
to eliminate the spurious `extended' sources in nebulous regions,
caused by single pixel blips on top the the nebulosity, is working well
in the test region rho Oph. She and Tom Jarrett are developing an
algorithm to identify real stars in nebulous regions using an average
measure of the background within 50 pixels of the source, compared to
the coadd-wide average background. GALWORKS is now successfully
rejecting false sources while retaining real stars on top of
nebulosity.
- T. Jarrett:
has been studying the star-galaxy
separation efficiency in Coma. He now has a completely cleaned Coma
database, for which all galaxies have been confirmed in NED or by plate
inspection. He and T. Chester have been studying several new
potentially useful star-galaxy separating parameters; they now have a
total of 9. The `shape' parameter and maxdn remain the most powerful,
but a new parameter, based on the average brightness in an annulus of
radius 5-7 pixels, shows promise of being particularly useful as it is
independent of magnitude, to first order.