From jwf@ipac.caltech.eduFri May 23 10:30:46 1997
Date: Wed, 7 May 1997 15:07:03 -0700 (PDT)
Subject: WG Mtg #121 Minutes

           IPAC 2MASS Working Group Meeting #121 Minutes

Attendees: R. Beck, T. Chester, R. Cutri, D. Engler, T. Evans,
           J. Fowler, T. Jarrett, B. Light, J. Mazzarella,
           H. McCallon, S. Wheelock, J. White


1.) Processing Status
2.) Review Schedules
3.) Observing Resumption
4.) PSFs
5.) Hot Pixels
6.) Repeatability Analysis of Three-Channel Data


1.) Processing Status

R. Cutri reported that the 2MAPPS processing of night 55, otherwise known as
970423, was scheduled to begin as soon as the meeting ended. This run will use
the new DARKS subsystem to force off certain hot pixels (see item 5 below) in
the masks and also to force off pixels turned off by DFLAT in the 970418
processing (mostly pixels along the edge of the arrays). The data from this
night have never been input to 2MAPPS before, so this run will also be
something of a test of how the system reacts to never-before-seen data.

2.) Review Schedules

R. Cutri announced that the next Science Team Meeting will be held at IPAC on
June 4 and 5 and will be primarily an Operations Readiness Review for the
Observatory, although some discussion of 2MAPPS status will take place on the
second day of the meeting. For this purpose, subsystem cognizant engineers are
requested to send information concerning subsystem status and liens to R.
Cutri by May 14. The External Review Board Meeting will take place in Amherst
in the second week of July.

3.) Observing Resumption

Data will begin to arrive from the Observatory next week as observing resumes.
Engineering tests are planned to support studies of the Read1/Read2-Read1
offset and repeatability, dithering pattern adjustments, electronic noise (the
cabling has been rearranged to reduce this), drive gear problems, and flexure.
A resident observer has not yet been hired, and so three IPAC personnel will
be taking turns doing two-week stints in this position. This includes R.
Cutri, H. McCallon, and Brant Nelson, a newly hired postdoc from UCLA. The
observatory will be shut down for the month of August, and a permanent
resident observer should be hired by the time activity resumes after that.

4.) PSFs

Point-Spread Functions (PSFs) have been computed as a function of focal-plane
position for all bands from one dense scan (041) and separately from a
concatenation of sparse scans in 970418. The only differences between the
dense and sparse cases was due to lower sample volumes from the sparse scans.
The variability over the focal plane appears negligible in all bands, although
a very small systematic effect appears to be discernible. The PSFs in J and H
are round and sharp, but those in K are a bit elongated in the cross-scan
direction. This may not present a problem, since the repeatability appears to
be very good. Subsequent analysis of the PSFs in scan 044 shows that the K PSF
is more compact and round than in either scan 041 or the low-density scans.

5.) Hot Pixels

The "hot pixel" analysis has revealed that seven pixels in K are extremely
erratic, i.e., they appear to generate electrons spontaneously at random times
for periods of about 10 or 20 seconds. These seven pixels were found to be
erratic on every scan that was studied by J. Mazzarella using a utility
program especially written for this purpose by G. Kopan. In addition, another
48 pixels in K and one in H exhibit this behavior at a lower frequency, i.e.,
not in every scan studied. The new version of DARKS allows a pixel list to be
specified for forced masking, and tonight's run will use this to turn off the
seven worst pixels in K. In addition, J. Fowler will clone the PSF program and
modify it to print out frame snips centered on hot pixels so that some insight
into the shapes can be gained. It is hoped that this might lead to a good way
to distinguish the hot-pixel syndrome from persistence due to bright sources,
in case some method of automated detection turns out to be necessary. It is
hoped that offline analysis and forced masking will suffice.

6.) Repeatability Analysis of Three-Channel Data

R. Cutri displayed results from a repeatability analysis of point sources
obtained from overlapping scans in 970418. Although the point-source
extraction was done with PROPHOT PSFs from the protocamera, the positional and
photometric repeatability was nevertheless excellent.