Subject: APO 3.5m user's committee meeting, 12/17/2001

From: strauss@astro.Princeton.EDU

Submitted: Wed, 19 Dec 2001 08:54:06 -0500 (EST)

Message number: 538 (previous: 537, next: 539 up: Index)

  Apache Point Observatory 3.5m User's Committee Meeting
		December 17, 2001

Attending: Mike Shull, Bruce Gillespie, Ed Turner, Michael Strauss,
Lew Hobbs, Bruce Balick, Jon Holtzman, Rene Walterbos, Alan Uomoto,
Jon Morse

  -Current status of DIS upgrade
  -Results from the Board of Governor's meeting
  -Discussion of future priorities for the observatory: instrument and
	      telescope projects. 

*********************Status on DIS upgrade.******************************

There is good news and there is bad news. The good news is that the
CCD linearity and full-well problems that have been stalling progress
at UW have been solved.  However, as of late last week, the red chip
was significantly contaminated by some sort of deposit on its surface.
People are trying to figure out what happened, what the contaminant
is, how serious it is, etc.  The plan had been to install the new
chips in the instrument during the January bright run, but this latest
set-back makes this unlikely (although not impossible).  More news
will be forthcoming, as this contamination problem gets sorted. out. 

Over the last months, Ed Turner has been scheduling blocks of time
during which the DIS is not scheduled, with the upgrade in mind.
However, the schedule for the upgrade has slipped enough times now
that it is no longer worthwhile doing this, and he will no longer
distort the schedule.  Thus when the upgrade actually does happen,
there will inevitably be some DIS users who will end up having to
switch their time, or go to a back-up program with a different

***********What happened at the Board of Governor's meeting. **************

The budget requests for operations and sinking funds were accepted.  The
Capital Improvement Fund (CIF), which is used for improvements around
the telescope, has been incremented slightly.  

Ed Turner was reappointed as director of the 3.5m. 
Congratulations from the User's Committee!

There was much discussion of mid-term and long-term plans for the
telescope, which in fact is the next item we discussed in the user's
committee meeting. 

***************Next Year's Priorities*************************

The CIF funds are meant for upgrade to the telescope and/or
instruments, and are roughly of the order of $300K/year.  Now is the
time to set priorities over the next year or two for what to do with
this money.

  First, there are two CIF projects from 2001 that will be continuing
into 2002:
    The DIS upgrade (see above) including new detectors and
improvements to the optics. 
    The telescope observing software upgrade, spearheaded by Russ Owen
and Craig Loomis, now in alpha testing. 

  There is also a major telescope improvement item in progress, namely
work on the baffling. 

  On the table at the moment are four major possible initiatives:

   -The new top-end, with a new more rigid support structure.  This
would include mechanisms for closed-loop focussing, but does not
include earlier suggestions of tip-tilt or fast guiding.

   -Upgrades to the U. Chicago Echelle spectrograph.

   -Upgrades and enhancements to the planned NIC-FPS, the near-infrared
imager which the U. Colorado folks are building. 

   -A near-infrared spectrograph to be built by JHU. 

  We had a detailed discussion of the three instrumentation programs.

		-Echelle Spectrograph

   Lew Hobbs: Don York has written a document describing the current
status of the instrument, stressing the fact that it is read-noise
limited for objects much fainter than V=16 (given the fact that you
can't integrate too long without being overwhelmed by cosmic rays),
and its resolution is limited by its pixel size.  

  This document can be read on the web at:

  If one could upgrade to a new Marconi 4KX2K chip with substantially
smaller pixels and lower readnoise, one would avoid both these
problems; the ability to go to fainter objects being the main science

  The current set-up (with readnoise of 7 e-) gives complete spectral
coverage from 3600-10,000 A.  With the new chip, the spectral coverage
would be quite similar, although there would be gaps beyond 9400 A. 

The Marconi chips are the same that will be used in WFPC3 on HST.
These are said to have very low fringing even out to a micron.  These
chips deliver readnoise in the range of 2-5 e-; we would definitely
want one closer to the lower end of that range!  

  It is unclear whether we want a blue- or red-optimized chip; indeed,
the user's committee would like more details on the properties of the

  With the current chip, the instrument detects 10 e- per hour per
pixel near 7000 A (the peak of its response), or 50 e- per hour per
resolution element.  This means that you're readnoise limited in this
time, although with the new chip, you beat the readnoise limit in two
hours integration (which gives you an acceptable cosmic-ray rate
because of the smaller pixels). 

  Thus, an all-night exposure made up of 5 two-hour exposures on a
V=19 objects gives S/N = 22 per resolution element at 7000 A. 

  In addition, they will also put in an antireflection coating on some
of the refracting elements, improving the throughput by a factor of 2
(a factor not taken into account in the above calculation.

  The guider can't currently work much fainter than 16, so it would be
necessary to upgrade the guider to take advantage of the ability of
the spectrograph to go substantially fainter.

  Note that with the ability to go fainter and observe large numbers
of extragalactic objects, a much wider complement of the ARC community
will be interested in using this instrument. 

	    -NIC-FPS: Current status and possible upgrade

  There is a pair of PDF documents describing this instrument at:

  John Morse: When U. Colorado joined the ARC consortium, they agreed
to build a 1KX1K near-infrared imager, called NIC-FPS.  They are now
considering two possible enhancements of this, for which they are
asking for CIF funds:

   1.  To build the optics and dewar large enough such that if in the future,
funds are found for a 2KX2K chip, that it can be put into the existing
instrument.  OR

   2.  To put this instrument on a dedicated corner port, which would
require acquiring a rotator and guider for it.

  For option 1, building the instrument to make room for a 2KX2K
instrument (0.3" pixels, or 10 arcmin for the full instrument), would
require 7" optics.  These optics are quite expensive, and outside the
current budget of the instrument; the difference would be requested
from CIF funds.  Because these optics are more complicated, they would
take substantially longer to build, meaning that the final delivery of
the instrument would be roughly one year later.  That is, the current
baseline plan has the 1K instrument delivered in late 2003; if it were
built with the larger optics, it would see first light a year after

  A major main science driver for the wider field of view is surveys of
diffuse Galactic nebulae. 

  The current plan with 1K optics would be first light in late 2003.
  With the 2K optics would be a year after that.

The science case for fast instrument change (i.e., 1 minute rather
than 15 minutes for a normal instrument without a dedicated port)
needs further discussion.

  GRIM (256X256) has a read-noise of 150 e-, while modern chips from
Rockwell have 10 e- readnoise; a huge improvement!  There are NGST
prototype devices, which have a fast-read guide mode, allowing an
increase in dynamic range.  

  Downstream, we could consider a 4KX4K imager, made of a mosaic of
2K's.  A number of people are now figuring out how to package such

		-A JHU-Chicago Near-Infrared Spectrograph

  Alan Uomoto: There are funds available to build an instrument at
JHU.  A brief e-mail describing the proposed instrument can be 
found at:

The SDSS has discovered lots of objects which require follow-up with
near-IR spectroscopy, especially high-redshift quasars and brown
dwarfs.  Thus we suggest building a near-infrared spectrograph, which
could cover the spectral range from 0.85 to 2.4 microns (zJHK) in two
passes at resolution R=500.  There could be a series of grisms on a
turret wheel, offering resolutions up to 4000 (although at lower
throughput), although the final choice of resolutions is still to be

  There would also be a slit wheel, with slits of width 0.5" to 2",
and possibly a Integral Field Unit as well. 

		-Concluding remarks and miscellaneous

  This represents the start of what should be an ARC-wide discussion
of what our priorities for the next few years really are.  There will
be a pair of face-to-face discussions of this at the upcoming AAS
meeting (see apo35-general #533):
   Tuesday, January 8, 5:30-7:30 PM
   Wednesday, January 9, 3:30-5:30 PM

  Both will be held in the Bancroft Room at the Hilton (i.e., the
hotel at which the AAS meeting is being held).  If you are planning to
attend, please be sure to let Gretchen (

  On other instrumentation news:
  Chris Stubbs' views of his planned wide-field optical imager for the
3.5m are changing; he is now considering using a series of dichroics
to image simultaneously in many bands.   This is at least partly due
to the realization that our f/10 secondary isn't ideal for wide-field 

Morse: We've been talking about building an f/5 secondary for ARC,
which would allow a much wider field of view.  This would require
retrofitting current instruments, of course; it is also quite

  There was some discussion about whether it would make sense to have
two secondaries for the telescope, and mechanisms for swapping them.

  Finally, there is one open half-nights coming up: namely the first
half of Dec 28.  If you're interested, please let Ed Turner know as
soon as possible.

  Minutes of last meeting approved. 

  The next meeting will be held Friday, January 18, 2002, at 11:30 AM East
Coast time. 

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