Subject: 06/17/02 APO 3.5m User's Committee meeting minutes

From: strauss@astro.Princeton.EDU

Submitted: Tue, 18 Jun 2002 08:50:39 -0400 (EDT)

Message number: 586 (previous: 585, next: 587 up: Index)

  Apache Point Observatory 3.5m User's Committee Meeting
		June 17, 2002

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

Absent: Rene Walterbos, Chris Stubbs

Status of Instrument programs
	DIS upgrade status and fringing
	IR Spec

Shutdown plans


Communications Issues

***************DIS Upgrade***********************
  The new blue chip is installed and working.  Work continues on the damaged chip; we
may know for sure this week if it is salvageable, and if it is good,
we'll get this chip as a spare.  
  Holtzman: The throughput on the blue looks better than before.
We're getting 20% system throughput (i.e., including telescope),
4300-5300A.  It should get even better after realuminization. 
  The throughput on the red side looks somewhat poorer, however; total
system throughput is 10-11% (used to be more like 15%).  Could this be
due to the medium resolution grating?  We need to recheck this with
the low-resolution grating.  We have engineering time in a week to
redo this measurement.  
  We're eager to hear from people with experience on the new and old
DIS: are things really better?  
  Strauss: our experience with spectroscopy of faint red objects is
that with proper flatfielding, we're going about as deep as before. 

  The red chip shows very strong fringing in the red (not
surprisingly; it is a thinned chip).  Strauss: we believe we see
flexure in the system at the level of a pixel or two, which limits the
ability to flatfield in the presence of fringing, for very faint, red
objects .  We find that we can do a good job by taking a flatfield
immediately following an object exposure (now that the mirror covers
are operable remotely by the observing specialists, this is straightforward).  

  Balick: We need to keep the documentation on DIS up to date.  Jon
Holtzman's writeup from March is very useful; can we keep these going? 

  The lore and knowledge about all the instruments needs to be put into
one place.  Gillespie will make this a priority. 
  Morse: There are some design re-evaluations for NIC-FPS, which do
not affect functionality.  The old design had the Fabry-Perot etalon
stationary (it is cryogenic), but this complicated the optics in a
variety of ways, so it is better to allow the etalon to move, which
will save time and money on the optics.  This will allow everything to
be on-axis.  This should help a bit on image quality and throughput,
and a lot on alignment.

  We've looked into the ghost image problem; the most serious ghosts
are down by 20 magnitudes (other than from the etalon itself, which is
a generic problem with these sort of devices).

  The NIC-FPS team was at APO last week, talking to the folks there
about interface issues.

  Turner: The formal decision has been made to put this instrument on
the Nasmyth port. 

  Morse is planning to put in a proposal to the NSF ATI (advanced
technology instrumentation) program for filters, etc.  

*******************IR Spectrograph**************
All the administrative arrangements between JHU, Chicago and ARC for
this instrument are falling into place. 
Uomoto: A design review was held in JHU on May 21.  Two major
recommendations came out of this review. 
  1.  Use the Rockwell HAWAII-1RG chip.  This is more expensive than
the baselined Rockwell HAWAII-1 chip, but is much better in a variety
of ways. 
  2.  Consider gratings rather than grisms, as they are less expensive.  

The latter requires rethinking the optical path, but we think we have
a design that will work.  The optics will not be trivial; among other
things, it requires a diamond-turned calcium fluoride element.  We
haven't made the final decision on the grism/grating choice.

  The grisms are about 10% more throughput, however (at least on
paper); there are no polarization losses.

Note that the spectrum will be along the diagonal of the chip, to
maximize spectral coverage. 

A full report on the instrument can be found at:

A discussion of the design review, and results from it, are at:

**************Shutdown plans*********************
We will realuminize the primary at KPNO during the monsoon season,
mid-July (which we have never been able to do before). 

There are serious concerns with the enclosure shutters; they need some
real repairs.  We will not do the entire job for this shutdown; we'll
get through about 20% of all the to-do's for this. 

Camron Hastings is leaving us, to pursue his interests in the medical
profession.  We have a new person recruited, William Ketzeback.  He's
worked at the VLA, has optics experience, has worked at Flagstaff.
He'll come in July, a month before Camron leaves.

*************Communications issues******************
Keep an eye on changes in the schedules (always posted to
apo35-general when revised); see the discussion at:

  If at all possible, observers should get in touch with the site
between 48 and 24 hours (via e-mail to before
the start of the run, to discuss the instrument setup, and to make it
clear that they are aware that they have the time (there are still
occasionally no-shows from people who literally forget that they have
time assigned).  The site will do its best to accomodate same-day
changes to an observing plan, but giving them ample advance warning is
always the best policy. 

  The last meetings' minutes were approved. 

  The next meeting will be held at 11:30 AM EDT on July 29.

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