IPAC 2MASS Science and Analysis Working Group Meeting #3 Minutes

IPAC 2MASS Science and Analysis Working Group Meeting #3 Minutes, 9/20/95

Attendees: C. Beichman, T. Chester, L. Fullmer, T. Jarrett, D. Kirkpatrick, G. Laughlin, C. Lonsdale, M. Moshir, S. Terebey

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.