Subject: APO 3.5m User's committee meeting, 03/11/02
From: strauss@astro.Princeton.EDU
Submitted: Wed, 13 Mar 2002 19:24:54 -0500 (EST)
Message number: 558
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Apache Point Observatory 3.5m User's Committee Meeting
March 11, 2002
Attending: Bruce Gillespie, Ed Turner, Michael Strauss, Lew Hobbs, Jon
Holtzman, Rene Walterbos, Chris Stubbs, Alan Uomoto, Bruce Balick,
Mike Shull
**********Status of the DIS upgrade:*******************************
Gillespie talked this morning with Peter Dougherty, who is one of
the main U. Washington people involved in the DIS upgrade effort.
There have been a number of problems with the installation, involving
in part problems with the vacuum on the dewars. These are now mostly
under control. Moreover, the blue camera cold strap was not quite
touching the chip; it is now fixed. The red camera is ready to go on
the sky. It looks very good. There does seem to be substantial
fringing beyond 7000-8000A (as can be expected for this type of chip).
However, the throughput of the blue camera seems low; there is a
possibility that the lenslet in front of the blue chip has the wrong
coating, which cuts about 50% of the light below 4500A. This should
be fairly straightforward to replace or fix, but this should be made a
high priority task.
[Note added by Gillespie two days later:
The coating on the blue camera field flattening lens was
mis-specified (got the same coating as the red lens, our mistake).
The vendor kept a spare uncoated blue lens, and can put the proper
coating on it and have it here in two to three weeks. We have ordered
the lens and will put in the replacement in April. We will use DIS
as-is in the meantime with the degraded blue throughput, which will be
characterized starting tonight (i.e., Wednesday, March 13).]
There is still a small amount of work to align the blue chip and
thus focus the blue camera. This should be complete by March 13.
We are ready to go ahead and cut the relevant holes in the DIS
manifold to run all the relevant cables. That is, we're go for
finishing the DIS upgrade. The instrument will be on the sky for
testing on Wednesday night, March 13.
***************DIS grating configurations:********************
Russet McMillan sent out a message (apo35-general 555) discussing
various configurations for the gratings. The point is that there are
two slots for grating pairs in the spectrograph, and three grating pairs
available. Inserting new gratings in the spectrographs is
time-consuming, and has the potential to damage the gratings. If we
could settle upon a default set to be used most of the time, life
would be much easier. With the DIS upgrade, previous experience on
grating choices needs to be rethought.
Note that these chips support on-chip rebinning (although this
hasn't been exercised in all possible configurations).
We realize we don't know all the variables yet. In particular, we
need to know the relative throughputs of the various grating
combinations, and the relative resolutions (Angstroms per resolution
element) for default slit widths. Once the upgraded DIS is available,
we need to take 1/2 night, and measure the throughput of the
different configurations at a variety of airmasses. One possibility
is to use the upcoming DIS engineering time on March 27-28. Before
that time, DIS will be used for science, which will give us initial
experience to help define this engineering run. In the meantime, DIS
users will need to think carefully about which gratings they need.
Another possibility is to get rid of the imaging mode, and put the
third set of gratings in there. But imaging mode is still very
valuable, e.g., for aligning slit masks, and may become more used
with the improved chips (although, because DIS has substantial more
optics than does SPICAM, the latter is probably superior for most
imaging programs).
Jon Holzman volunteers to coordinate the job of gathering the
relevant information on how to settle these questions: throughput,
resolution, readnoise, etc.
************************Time sharing with WIYN********************
Gillespie: We've been discussing with the WIYN folks the possibility
of sharing time between our two telescopes, given the fact that the
telescope instruments are quite different. They are continuing to push on
wide-field imaging capabilities on WIYN. We could have some input on the
design of their next-generation imager. If anyone would like to
attend the meeting in which this will be discussed (next
Monday/Tuesday at NOAO), Gillespie could wangle you an invitation.
Contact Gillespie if you have any specific
thoughts/suggestions/desires about the instrument.
************************Camron is leaving us!************************
Turner: Camron is planning to leave us this summer, and we'll need to
start looking for a replacement. We're about to put a job notice out
on the AAS job register. If anyone is aware of candidates, please
encourage them to apply. The position will be filled in late summer.
************************Scheduling**********************************
[Editor's note: Ed Turner had to leave early at this point of the
meeting.]
Every three months, the TAC's from the various ARC institutions give
Ed Turner a ranked list of telescope proposals from their institution.
Working down these lists, Ed does the scheduling process largely in a
vacuum. He can't always discern the sense of the individual TACs,
which can be difficult when, e.g., a somewhat lower-ranked proposal
has stringent constraints on when the observations might take place.
This can mean that it is impossible to schedule proposals which,
although not the highest-ranked proposal, are still highly regarded by
their TACs. This suggests that TACs should organize proposals not
just in scientific quality order, but also in decreasing requirements
on their scheduling. In this context, imagine a proposal which asks
for 4 half-nights, one of which *must* be the second half of April 4
for an occultation observation, and the remainder to be scheduled any
time. If the TAC found this proposal compelling, they may find it
useful to split it into two, where the part asking for April 4 is
particularly highly ranked (i.e., to be given priority in scheduling).
Ed Turner needs to communicate in detail with the TAC's to explain
what the failure modes in the scheduling are, so the TAC's (and
proposal writers!) can adjust their proposals accordingly.
We discussed the possibility of a meeting of the User's Committee
and the institutional TACs/schedulers, to hash this out.
We discussed some other, more radical ideas: queue scheduling, and
block scheduling (where Institution X is given a block of 10 nights,
to schedule internally among themselves).
The last meetings' minutes were approved.
The next meeting will be held at 11:30 AM EST on April 15.
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