Subject: ARC 3.5m User's committee meeting, Jan 13, 2003

From: strauss@astro.Princeton.EDU

Submitted: Tue, 21 Jan 2003 09:57:38 -0500 (EST)

Message number: 650 (previous: 649, next: 651 up: Index)

  Apache Point Observatory 3.5m User's Committee Meeting
		January 13, 2003

Attending: Bruce Gillespie, Ed Turner, Michael Strauss, Alan Uomoto,
Jon Holtzman, Jon Morse, Al Harper, Don York, Bruce Balick, Mike Shull

Absent: Chris Stubbs, Rene Walterbos

  On Monday and Tuesday evenings of last week, members of the ARC
community (roughly 15 people in each meeting) met in a pair of 2-hour
meetings during the AAS meeting in Seattle.  The primary focus of
those meetings (and indeed, the current meeting) was a discussion of
the various projects suggested to receive CIF funds this year, and how
we might prioritize these projects.  Bruce Gillespie will distribute
minutes from last week's meeting.

  There are seven major projects which were considered; here is the
jist of the discussion: 

   The JHU/Chicago Near-IR spectrograph
     An NSF proposal for this has been submitted, which, if
     successful, would help pay for the building of this instrument.  The
     instrument will be built at JHU, by Alan Uomoto and his team.
     Its ownership would then be transferred to Chicago, as part of
     the deal by which JHU got telescope time from Chicago.  If the NSF proposal
     is unsuccessful, this instrument becomes quite a bit more
     expensive for ARC, because CIF funds could be required to make up
     any shortfall. 

   The NIC-FPS
     The basic instrument is being built with funds from the
     University of Colorado as part of their buy-in to the 3.5m
     telescope.  They have submitted a proposal to the
     NSF, largely to buy a large suite of filters.  The CIF
     funds would be to get a z filter (not included in the NSF proposal)
     plus spare filters, plus a final payment on the detector.

   Echelle upgrade
     The instrument is currently read-noise limited for faint-object
     spectroscopy.  Don York plans to submit an NSF proposal for a
     really low-read-noise chip, which assumes a cost-sharing with
     ARC, whereby the CIF would pay for the detector (and the NSF
     would pay for the manpower, electronics, etc).  The estimated 
     cost of such a chip is $130K, of which $30K may be supplied by
     George Wallerstein.  

   UW multi-band imager
     This instrument would use dichroics to image in four broad bands
     simultaneously.  It would have a field of view of order 5
     arcminutes.  The CIF funds would support the UW technical staff
     who would build it. 

   "New top end" 
     This refers to a series of improvements to the primary, secondary
     and tertiary mirror supports to improve image quality, both by
     removing slow-term drifts in collimation, and removing
     higher-speed harmonic image motion.  A related issue is to put in
     the hardware to allow fast (tip-tilt) guiding at the secondary or

   Recovery of DIS UV sensitivity
     We have long known that the coatings of the optics of DIS do not
     transmit below roughly 3800A.  To fix this would cost of order 

   Telescope engineering projects/maintenance/improvements
      There is a long list of maintenance items that Jon Davis has
      compiled, concerning the smooth operation of the telescope, and
      the prevention of catastrophic failures (like the failure of the 
      telescope drives last month).  The main items are to improve
      the robustness of: 
        The telescope drives 
        The enclosure shutters
        The enclosure rotator system

   In addition, there are a number of CIF projects from previous years
   that are not quite complete, and which should be completed in 2003: 
    NIC-FPS detector upgrade
    Observing software upgrade
    Echelle slit guide camera upgrade
    Finishing optics upgrade for DIS	      
  While everyone agreed that everything on this list was meritorious,
and we would love to have everything, we would prefer to put our
resources to being successful on a small number (2-3) of the items
above, rather than spreading ourselves thinly, and making slow
progress on all of the above.  Even if we were in the happy position
of having funds for all of the above, we would be limited by personnel
(i.e., many of the key people would have important responsibilities
for more than one item in the above list).  

  We spent much of this meeting in a discussion of the balance between
instrumentation, and work on the telescope.  Ed Turner emphasized that
when he first came on as director, everyone agreed that the telescope
needed attention and that was more important than instrumentation for
the short term.  The telescope performance is dramatically improved
since then, and the concensus has been that more resources should be
put towards instrumentation.  Having said that, it is clear that
the telescope is the limiting factor in image quality on at least some
nights (for imaging programs), and it would be very good to improve on that.  

  A full characterization of the image quality problems is needed.
We know that the telescope collimation does occasionally jump, and an
on-going Shack-Hartmann monitoring project is trying to figure out
what is going on.  It was not clear to all of us whether this was the
full story behind the degraded images on the best-seeing nights, or
whether there was more going on as well.  Al Harper reported that he
has often seen images (with GRIM) in which stars appear double; he
thought this might be due to oscillations in the primary mirror

  This last really sounded like something was broken, and fixing it
belongs in a different category from a general program of telescope
improvements to fix the image quality. 

  We all agreed that further progress on image quality will require
one or more dedicated people to investigate the problem(s).  In the
meantime, it would be very useful to have a summary of:
   -All known and possible problems affecting image quality
	(wind-shake?  Primary mirror support?  Not enough tension 
	in the secondary truss? Catastrophic slippage giving rise to
	double images? Focus instability? High-speed vibrations caused
	by the drives?)
   -What is currently known (and not known) about their contribution
        to the error budget. 
   -What we need to do to get more information about these things. 

  Without this in hand, it is difficult to make decisions of the
relative importance of these different items. 

  Bruce Gillespie emphasized that we need to have this discussion of
priorities, in the context of what the ARC institutions actually want
to do scientifically.  For example, do we want to tool ourselves up as
a telescope optimized as a time-domain instrument, able to respond
quickly to synoptic opportunities?  Or do we want to emphasize superb
image quality?  An all-purpose observatory?  This ended the discussion
(for this meeting) of this important question. 

  DIS optics: In the last day or two, a problem in the manufacture of
the new optics for the DIS (red side) was found; it will have to be
sent back to the manufacturers.  The blue side is fine, and the new
blue-side optics will be installed over the next week or so. 

  Last month's meeting minutes are approved. 

  Next meeting on Monday, February 3 at 11:30 AM East Coast Time. 


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