Date: Wed, 8 Apr 1998 09:33:06 -0700 (PDT)
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To: 2mass
Subject: IPAC 2MASS WG Mtg #148 Minutes
Cc: chas,, stiening, bgreen
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Status: RO

           IPAC 2MASS Working Group Meeting #148 Minutes

Attendees: R. Beck, R. Cutri, S. van Dyk, D. Engler, T. Evans,
           J. Fowler, L. Fullmer, T. Jarrett, D. Kirkpatrick,
           G. Kopan, J. Mazzarella, H. McCallon, B. Nelson,
           B. Wheaton, S. Wheelock, J. White


1.) Northern Observatory Changes
2.) 2MAPPS 2.0 RTB Status 


1.) Northern Observatory Changes

    R. Cutri reported that R. Stiening will be at Mt. Hopkins
next week to make several hardware and procedural changes. Some
improvements to the telescope control are planned; these should
make the actual pointing much closer to the reported commanded
pointing at the start of each scan, providing better initial
estimates for pointing reconstruction. Changes in the camera
electronics are also planned which will fix a recurring problem
in the readout of the first column in each array quadrant; these
improvements will probably alter the dark and responsivity of the
pixels in the affected columns, and so a new MRD (masks,
responsivities, and darks) time period will be defined beginning
when the changes are finished.
    In addition, shorter dark sequences are planned; dark "scans"
will be 48 frames instead of 278. Twilight flat sequences will
also be modified so that only every fifth frame is recorded. This
will reduce data volume; it is not known whether it will
significantly increase the estimation error in the
responsivities, but the new five-night averaging procedure should
help attenuate any loss of accuracy.
    It has also been suggested to take twilight flat sequences in
the evening instead of the morning; this can be tried as an
experiment, but there is concern that the relationship between
each pixel's responsivity and the frame median when the array is
saturated or has recently been saturated might be very different
from observing conditions. Although it has been claimed that the
arrays recover from saturation in seconds or minutes, that only
relieves concern about whether the hardware is ready for science
observations after being saturated by evening twilight. For the
responsivity relationships to be right, all pixels would have to
have identical post-saturation relaxation behavior, which seems
unlikely. It was proposed that evening and morning flat sequences
be taken for experimental purposes; this has been done in the
past, and differences at the 10% percent level have been seen,
but the differences at the 1-percentile and 99-percentile are
more like 2%, which is not so far from night-to-night differences
in morning flat sequences.

2.) 2MAPPS 2.0 RTB Status

    The team was polled for items preventing 2MAPPS 2.0 from
going into production. The items identified were as follows.

     A.) PROPHOT has a residual problem involving the environment
     around very bright stars producing  peak pixel' values that
     are very negative; these cause format problems in table-file
     interfaces; B. Wheaton will clip the peak pixel values and
     flag them to prevent this.

     B.) Final decisions of which hot pixels to mask in the
     various MRD time intervals remain to be made; R. Cutri, J.
     Mazzarella, and J. Fowler will form a splinter group to tie
     this item off.

     C.) H. McCallon requested acceptance of a new POSMAN
     delivery which will provide better diagnostics (enhancements
     and reduction of the main POSMAN input to the QUALITY
     subsystem, the QAPM file, and magnitude filtering of the
     spectral-combination counters to reduce noise false alarms)
     and allow more flexibility in accepting Tycho matches
     (maximum distance threshold enlargement option and access of
     Tycho stars from adjacent tiles to compensate a declination
     cosine effect in the tile geometry). These changes were
     found acceptable. Howard also stressed that scan overlap
     position discrepancy analysis was extremely useful in
     diagnosing problem scans (and possibly fixing them) and
     should be considered for pipeline inclusion in some later
     version of 2MAPPS, but this sort of analysis must remain
     offline for the present.