Subject: Minutes of APO User's Committee Meeting, April 14, 1997

From: strauss@astro.Princeton.EDU

Submitted: Tue, 15 Apr 1997 09:18:19 -0400 (EDT)

Message number: 138 (previous: 137, next: 139 up: Index)

   Minutes of APO 3.5m User's Committee Phone Conference
		  Monday, April 14, 1997

   Attending: Bruce Gillespie, Ed Turner (Chair), Michael Strauss
(taking minutes), Chris Stubbs, Jon Holtzmann, Lew Hobbs, Jeff Secker.

  The current status of DIS
  The Primary Mirror Support System, other recent developments
  Staffing Issues

	The Current Status of DIS

(Lines which start with '>' are taken from an e-mail from Alan Uomoto
on April 11)

>Jon Brinkmann fixed the DIS noise problem.  The problem was a ground
>loop in the coax connection to the mid-level from the instrument.  Jon
>had to disable the coax driver to make the fiber driver work, so one
>wire needs to be replaced to get back to the old state.

This apparently fixes both the fixed pattern noise (seen on the blue
side) and the bimodal bias problem seen in the red side. 

New DIS Intermediate Dispersion Gratings:
  The following is the specifications of the suggested new gratings;
they are roughly $2388 each. 
>Adding intermediate dispersion gratings is part of the DIS refurbishment
>plan.  Specifications for the new gratings are shown here; compare with
>the existing low and high dispersion gratings:
> Groove spacing (lines/mm)
>BLUE	300	600	1200
>RED	150	300	 830
>  Detector scale (A/pix)
>----------------------------		Crossover wavelength is 5350 A
>BLUE	6.2	3.1	1.6		BLUE PIXEL SIZE is 27 microns (1.1")
>RED	7.0	3.5	1.1		RED PIXEL SIZE is 15 microns (0.61")
>Blue side wavelength coverage would be almost 1600 A, red side 2800.
>A popular setup might be 3800 to 8100 A with no gap.
>Sample efficiency curves are on
>and  For DIS, these curves should be shifted to shorter wavelengths
>by 5%.
  Gillespie pointed out that installing these gratings in DIS was not
a completely trivial job, and represented several man-days of work.
The committee agreed that Alan should go ahead and order them. 

DIS High Resolution Gratings
  The suggestion has been made that high-resolution gratings also be
available for DIS.  There is concern that they will be made obselete
by the echelle spectrograph, that they will be quite expensive, and
that they will have low throughput.  Of course, the echelle
spectrograph is not yet available (Hobbs estimates that it is unlikely
that the echelle will be delivered before October 1; January 1 might
be a better guess as to when it will be available to the user
community), and the echelle will not have a long-slit mode, by
  Bruce Balick of UW has been enthusiastic about getting these
gratings, and we agreed that we needed more information (specifics of
cost and throughput of these gratings, the demand for these gratings
throughout the user community, and the best estimate of the timescale
for the echelle) before we make a real decision. 

>Two stainless steel reflective air gap slits are being built (1.5 and 2.0
>arc second widths).  Success is not guaranteed; these are difficult because
>they need to be thin on one edge to clear the shutter.  If successful, I
>suggest building a 1.0 arc second slit and a plate with paired apertures of
>various sizes.  These four plates would be installed in a new slit wheel
>that can carry four slits and two filters.
Holtzman: the folks at NMSU are interested in wider slits as well,
3-4" wide.

Question: Are we still planning to close DIS down to fix the problem
with the UV throughput?  There was talk a few months ago to bring it
down the third quarter.  We definitely need to make this decision
before 3rd quarter proposals are due.

Watson and Ledlow are going to the mountain to show
observing specialists how to reduce DIS throughput data. 

		Primary Mirror Support System

Stubbs: Support system has been deficient for a long time.  Ground
work has been laid for switching to new system, an important component
of the three-year plan.  At some point recently while this work was
being done, there was an episode in which the switch between support
systems was done incompletely, with the consequence that the mirror
ended up with a transverse displacement.  The symptom was nasty coma
seen in the images; apparently the primary was bumping into one of the
earthquake bumpers, which also screwed up pointing.  Intensive work
last week has fixed the immediate problem, and as of last night,
the images look much better, although not perfect.  In the meantime,
all kinds of other problems were found in the old support system.
Rather than characterizing them and fixing them, we will switch to the
new system by the end of this month.

		Other Recent Developments
  Gillespie: Telescope optics and pointing have been stable over the
last two days.  Pointing is 10-30" off.  Tonight is set aside for
engineering, including a new pointing model.

  Recent computer problems with TCC crashes were due to funny
interaction between TCC and SPICAM computers; this has been fixed.

  Refiguring of the secondary: there is a proposal from Steward, which
looks promising.  A fixed-cost proposal, which is a good thing.
Delivery by August '98.  Further negotiations are in progress. 

  Guider: 512X512 thick guider chip will be replaced soon by 1KX1K thinned
chip, but it is delayed by a cable that has not yet been delivered. 

  Once the mirror support system is under control, the next major job
is to work on the baffling for the telescope. 

  A detailed plan exists for telescope collimation by Jeff Morgan at
UW.  This will be posted on a suitable web page.

	Staffing Issues 
Gillespie: Jim Fowler is leaving at the end of May, to go to the
Hobby-Eberly telescope.  A recruitment advertisement for his
replacement ("Computer Systems and Network Administrator") is going
out in a few days.  There will be a goodbye party for him and Charlie
Hull, tentatively on May 17. 

  Last meetings minutes approved.

  Next meeting is May 12, 1997. 12:30 EDT

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