Date: Thu, 10 Sep 1998 09:34:53 -0700 (PDT) To: 2mass Subject: IPAC 2MASS WG Meeting #164 Minutes Cc: chas, stiening, bgreen IPAC 2MASS Working Group Meeting #164 Minutes 9/8/98 Attendees: R. Cutri, S. Van Dyk, R. Beck, T. Evans, R. Hurt, J. White, J. Fowler, H. McCallon, S. Wheelock, R. Tam, D. Kirkpatrick, T. Jarrett, W. Wheaton AGENDA 1.) Project Update 2.) Biases and Corrections 3.) A Long, but Relatively Fruitless Discussion 4.) New Action Items <-- A New Feature in WG Minutes DISCUSSION 1.) Project Update Northern OPS at Mt Hopkins should resume this week. Nothing new from the southern facility, except the weather has not been great. Southern processing has begun, but not without a small hiccup. 980319s was run with the old PSFs, 980321s was run with the new. 980714s, a long night with particularly bad seeing, is being run tonight with the new production PSFs, and will allow derivation of the MAPCOR normalizations with the new PSFs. When the MAPCOR namelist values are derived, the processing will resume. 2.) Biases and Corrections S. Wheelock discussed the analysis of the cross-scan photometric bias/ calibration correction. The algorithm appears to work well for most scans; all of these seem to have the bias removed. Other scans have the bias "straightened out," but not quite right. A small bias offset still exists for these scans, which typically are high-stellar-density scans. A physical reason for the bias may be close to being understood: it appears to be something in the telescope optics. M. Skrutskie analyzed a focus test and found that the pupil image is slightly off-center. It may be possible to nudge the focus in the south some to correct for the photometric bias at the telescope. In the north the astigmatism is worse, so it may not be possible to do a telescope correction, but in the north, the photometric bias is a much smaller effect that probably does not require correction. The correction algorithms continue to be tested and will need more tuning for the southern processing. H. McCallon presented data showing significant improvements for the 971116n position reconstruction obtained via a "Martinizing" of contiguous survey scans. Each scan was broken down into 12 segments and average in-scan/x-scan position differences with respect to adjacent scans were computed. Through an iterative scheme all scan segments were adjusted to improve the overlap differences, and a table of in-scan/x-scan position corrections was built. The resulting corrections were applied to all survey extractions using linear interpolation between segment centers. The overlap position differences were regenerated, as well as the ACT residuals. Sigmas using all survey overlap data dropped from 0".186 and 0".159, to 0".133 and 0".128 for in-scan and x-scan, respectively. The resulting increase in ACT residuals was quite small, going from 0".115 and 0".094 to 0".122 and 0".106 for in-scan and x-scan, respectively. Improvements for problem scans were even more dramatic than indicated by the overall stats, especially for scan 113, which has no ACT's. It was decided not to include the position corrections in the Sampler release for several reasons. Consistency would require changing the extended point source positions as well, along with coadd headers, galaxy stamp headers, USNOA association distances, and asteroid association distances and match confidences. H. McCallon was tasked to scope out a plan for possible inclusion in the March release of an expanded approach using all available overlaps from the database. "The minimum requirement for the Spring 1999 data release is that positional uncertainties reflect reality," said R. Cutri. 3.) A Long, but Relatively Fruitless Discussion The positional uncertainties and positional reconstructions performed during the inevitable reprocessing of data in the future will subsequently have its effect on object names, which are derived from their (accurate) positions. The proposed 2MASS naming convention is accurate to one-hundredth of a time second and one-tenth of an arcsecond. Positions for sources, particularly point sources, may change by some fraction of 1", and so the adopted name must undoubtedly change. There will be two catalogs, due to reprocessing, the initial one and the final one, plus a cross-reference between the two. An overly long discussion ensued, with copious suggestions from J. Fowler, on how to avert this inevitable problem. Nothing was resolved regarding this important issue, for now. But, then, a solution will not be necessary until catalogs are re-released, although it would be nice to have a working plan in place to deal with this. Finally, T. Evans has sent around a URL containing information about her analysis with R. Tam on the MAPCOR error and its effects. R. Cutri encouraged all members of the 2MASS team to please look at the webpage. 4.) New Action Items %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % & ACTION ITEMS % % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% This will be a new feature of the WG minutes, and its format will likely evolve. Here, the new action items for the ensuing week will be listed, often directed at particular personnel. It is meant as a reminder, to be referenced as such. 1. For this next week, R. Cutri directed the few who had not yet tested the CatScan and Survey Visualizer web interface to do so. It is imperative that all 2MASS team members test the site and provide their input before the Sampler release. S. Van Dyk directed some general comments regarding the CatScan interface. He will direct pointed comments to J. Good and J. Mazzarella soon. Comments and suggestions from other 2MASS team members are still welcome and should be directed to Good and Mazz, being sure to cc R. Cutri in all communications.