From email@example.comWed Sep 10 14:43:12 1997 Date: Wed, 25 Jun 1997 16:25:58 -0700 (PDT) From: firstname.lastname@example.org To: email@example.com Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: WG Mtg #126 Minutes IPAC 2MASS Working Group Meeting #126 Minutes 6/24/97 Attendees: T. Evans, J. Fowler, H. McCallon, B. Wheaton, S. Wheelock, J. White AGENDA 1.) Saturation Analysis 2.) Minor Planet Catalog 3.) Vacation and Observing Schedules DISCUSSION 1.) Saturation Analysis B. Wheaton displayed some images pertaining to the saturation analysis he is now beginning. An IDL plot of a dark frame was remarkable in the detail it showed; individual pixel values were actually discernible. He also had two images obtained from UMASS via the web that showed pixel output versus integration time. These showed that some deviation from linear response does indeed occur over the entire range, and the sudden onset of saturation was also visible in each band, along with the nonmonotonic response afterwards. The relationship of saturation tagging to photometric requirements was discussed and found not to be straightforward (here "saturation" is used in the "soft saturation" sense, i.e., significant deviation from linear response at the high end). Some time back, an error tree was developed by J. Fowler, but the filling out of this tree with a quantitative error propagation model was assigned as a science team activity which has apparently been awaiting the completion of higher-priority tasks. Two uses for the improved saturation tagging were identified: (a.) pixels tagged as saturated are counted and bookkept in the point-source extraction processing, so corresponding photometry can be interpreted in the light of this information; (b.) Read1 saturation is used to trigger first-persistence- object photometric estimation. Neither of these seem to relate directly to the primary photometric requirements. Some discussion of how to proceed in the saturation analysis took place. The goal is to replace the single number currently used as a threshold for tagging a pixel value as saturated with an array of individual pixel values. It was suggested to begin the exploratory studies by computing recursive linear fits to each Read2 pixel vs. the dark-subtracted Read1 median for the corresponding frame in a morning twilight flat sequence (morning, so that the pixels will be going into saturation instead of coming out of it). Significant deviation from linearity can occur at the low end as well as the high end, because of noise dominating the low signal. For a given pixel, each linear fit should reject data points beyond N sigma from the previous iteration's fit, using the previous iteration's sigma (N = 2, TBD). Such an algorithm is used in DARKS to compute responsivity (except that the ordinate is a dark-subtracted Read2-Read1 pixel, and the abscissa is the corresponding frame median). Iteration ceases when (a.) the same data points are used in two successive iterations, or (b.) too many points have been rejected, or (c.) the maximum number of iterations is reached (TBD 100). Bill will pursue these and other ideas in the next few weeks. 2.) Minor Planet Catalog J. Fowler reported that work was fairly advanced on the Minor Planet Catalog (MPCAT) subsystem. At the science team meeting the first week of June, the desire was expressed for this to include periodic comets and any planets that might appear with high S/N in the 2MASS data. It is not clear whether this is feasible, but some concern was expressed that planet apparitions might get into the data base without being identified as such. 3.) Vacation and Observing Schedules J. Fowler reported that he will be on vacation from next Monday (June 30) through July 15. H. McCallon reported that he will be observing at Mt. Hopkins all of next week, probably the week after that, and possibly some of the subsequent week as well.