Date: Fri, 6 Mar 1998 12:46:09 -0800 (PST) Message-Id: <199803062046.MAA00905@colman.ipac.caltech.edu> To: 2mass Subject: IPAC 2MASS Working Group Mtg #145 Minutes Cc: chas, email@example.com, stiening, bgreen Content-Length: 6309 X-Lines: 138 Status: RO IPAC 2MASS Working Group Meeting #145 Minutes 3/03/98 Attendees: R. Beck, C. Beichman, T. Chester, R. Cutri, D. Engler, T. Evans, J. Fowler, L. Fullmer, T. Jarrett, D. Kirkpatrick, G. Kopan, H. McCallon, B. Nelson, B. Wheaton, S. Wheelock, J. White AGENDA 1.) Obsolete Saturation Parameter 2.) Science Team Meeting 3.) Photometric Error Estimates 4.) Southern Observatory Status 5.) Northern Observatory Status 6.) New 2MASS Hires DISCUSSION 1.) Obsolete Saturation Parameter B. Wheaton reported that in working on replacing the single- number soft-saturation values with individual-pixel values, he ran across a parameter named "hibad" that is used in DAOPHOT- derived aperture magnitude routines to characterize what is being replaced with the soft-saturation values (i.e., pixel values too high to be trusted). Code that references the hibad parameter is to be found in FREXAS, PROPHOT, and GALWORKS. Rather than change the code, the team decided to set the value of hibad to an impossibly high number (99999.9 was chosen) so that any tests of whether a pixel's value is greater than hibad will fail. All subsystem cognizant engineers are requested to verify that either their code does not use this parameter or else that its value is set to 99999.9. The full-image soft-saturation data are not quite ready, but the software modifications are ready for test using a full-image composed of a single value for all pixels. The first tests will use the value that has been used as the one-size-fits all value, 43000. 2.) Science Team Meeting R. Cutri reported that the Science Team Meeting on the previous day, 2 March 1998, had resulted in excellent reviews overall for 2MAPPS 2.0, with only a few relatively small liens to be removed in the next few weeks before production could begin. The only significant lien involves further tuning of MAPCOR parameters, since some concern remains about how bright-star artifacts are handled. It was also decided that a correction algorithm for J bias jumps will be implemented, but that will not be part of 2MAPPS 2.0; the risk of attempting to fix these bias jumps by hardware replacement was judged too high. Tests of the effectiveness of such algorithms are required by May 15, and if all goes well, inclusion in 2MAPPS should occur sometime this summer. In the short term, the goal is to freeze 2MAPPS 2.0 in two or three weeks. J. Fowler pointed out that a waiver may be needed for MPCAT, for which there is still no automated selection of the appropriate orbital element set for the observation epoch; adding this later should not impact data products, but it would make operations much easier and more reliable. 3.) Photometric Error Estimates One additional item that came out of the Science Team review was concern about the photometric error estimates are computed for aperture magnitudes. Single-frame aperture magnitudes have to be averaged over the multiple apparitions, and in the process the single-frame photometric uncertainties are use to compute the "refined" uncertainty of the averaged magnitude. Currently the uncertainty sent downstream is the larger of two that are computed differently. Code that performs this averaging exists in PFPOST, which does it for Read1 sources, and PROPHOT, which does it for Read2-Read1 sources. The goal has been for the two to operate as similarly as possible. Both currently compute the mean magnitude by inverse-variance-weighted averaging of the single- frame magnitudes in the flux domain (to accomodate negative contributions to the average). For such an average magnitude, the formally correct error variance is the inverse of the sum of the inverse of the input variances. But the code also computes the observed dispersion in magnitude values, estimates the population variance as N/N-1 times this dispersion, and then computes the reduced variance (divides by N), referred to as the "reduced population variance". This would be an appropriate error variance for an unweighted mean, but is formally not correct as an error variance for the inverse-variance-weighted mean. Nevertheless, the code passes on the larger of the two variances as a sort of conservative estimate. The concern, expressed primarily by M. Weinberg, is that testing of statistical significance is impaired by carrying an error variance that is not appropriate for the way in which the mean is computed, and also that the error model in the aperture photometry routine is apparently not considered correct, since its output is not trusted when the observed dispersion is larger. At the least, an unweighted mean should be used when the reduced population variance is used as the error estimate. A splinter group composed of R. Cutri, J. Fowler, and B. Wheaton will take the action item to resolve this issue. 4.) Southern Observatory Status R. Cutri reported that first-light data from the southern observatory are expected as early as Wednesday night. The front end of the pipeline has been tested as well as it can be to prepare for fast-turnaround processing of these data. Subsystem cognizant engineers are requested to deliver their southern- hemisphere NAMELIST files and any other relevant data files to /2massc/del/datas by the end of the day tomorrow (Wednesday). 5.) Northern Observatory Status Replacement of invar rods and recollimation of the northern telescope was discussed at the Science Team meeting. The working group expressed concern about whether this would make the PSF tables obsolete, necessitating another recomputation (a time- consuming activity, since many different seeing conditions must be processed). This issue was not entirely resolved, but since one outcome of the Science Team meeting was a caution by J. Elias to allow schedule time for retuning and recalibrating after hardware changes, and since some hardware changes may prove to be inevitable, it seems likely that the capability to recompute PSFs in a timely fashion would be prudent, and a need for it should be expected in the near term. 6.) New 2MASS Hires T. Chester reported that two people were being hired for the 2MASS project, a 2MASS Analyst and a 2MASS Science Liaison scientist.