Subject: Minutes of 3.5m User's Committee meeting, April 12, 1999
From: strauss@astro.Princeton.EDU
Submitted: Thu, 15 Apr 1999 08:53:13 -0400 (EDT)
Message number: 347
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Apache Point Observatory 3.5m User's Committee Meeting
*******************April 12, 1999**********************
Attending: Michael Strauss, Rene Walterbos, Bruce Gillespie, Ed
Turner, Jeff Brown, Chris Stubbs, Ed Kibblewhite, Alan Uomoto
********Differential Imaging Motion Monitor (DIMM):**********
Stubbs: This is an instrument to measure intrinsic seeing on the site,
built by Armin Rest of the University of Washington. It's a 8 or 10
inch telescope with a two-hole mask; one hole has a wedge on it to
split the two images of a star in the focal plane. Take very short
integrations of Polaris, and look at the differential motion of the
two images, to get one point in the power spectrum of seeing;
extrapolate to the free-air seeing. The data will be put onto the
Web. The instrument will temporarily be located close to the all-sky
camera. When the seeing gets much better than 1 arcsec, then one is
limited by the dome seeing of the DIMM itself. This will be mitigated
by finding a better location in the "airstream" for a permanent siting
in the future.
In any case,
comparison with 3.5m allows one to determine, e.g., whether the
degradation of images is due to instrinsic seeing, or a problem with
focus.
Check out the DIMM web site for more detail:
http://www.astro.washington.edu/rest/dimm
We are thinking about putting one of these into the dome itself.
Stubbs plans a meeting with Gunn and Carr to discuss the upgrade of
the DIS chips.
**************Status of new top-end and secondary:*************************
Ed Kibblewhite: I will report on progress on the top-end design at the
next meeting. There is a possibility of sharing effort with the 2.5m
people, who are thinking about further work on their top end as well.
Alan Uomoto: The guy in charge of our secondary at Steward has been
out of town for the last two weeks. He returns today, so we should
know where things stand this afternoon. Some data on the surface
structure function are available, but it hasn't yet been put in terms
of PSF, Strehl ratio, etc. See the appendix for an e-mail from Uomoto
about the secondary status.
The plan is to install this new mirror during the August shutdown.
***************April engineering shutdown:************************
The main task is to motorize the rotation of the tertiary mirror.
Once this is done, instrument changes between echelle and Naysmith
will take only a few minutes.
A slightly more modest schedule than original has been adopted,
partly to accomodate a time-critical NMSU program: coordinated
observations of Mars with the AOTF.
Shutdown work will start 21 April, interrupted for a few days for the
AOTF program. Shutdown starts again 26 April, and should be over May
5, if there are no unforeseen showstoppers or bad weather.
One difficult thing will be getting a collimated beam into the
echelle once this is done.
************Remote observing from non-VBNS sites:****************
The VBNS sites seem to have stopped complaining about internet
performance to APO. But from other sites, especially Washington State,
things are getting worse. Washington State is likely to get on vBNS
soon. Turner: Having a SLIP-PPP connection as a backup is something
we would always like to have. Stubbs: We can't guarantee decent
internet connection to anywhere on the planet; our effort should be
focussed on making the connectivity to our departments as good as it
can be.
Gillespie: We have relatively few people observing remotely from
non-APO sites; often these observing sessions are problematic. People
who are going to observe from a non-standard site should try things
out a day or two in advance, to make sure that they can actually make
the relevant internet connections.
Turner: All user's committee members should confirm that they have
SLIP-PPP modem capability in their observing room. The modem number
is 505-437-6149.
*****************Site report:*********************************
Gillespie: At the last user's committee meeting, we reported an
accident, involving the dome running into open hatch doors at the
intermediate level. We were able to recover mechanically, although we
lost one day of observing. We've ordered new doors with electronic
switches so the building would not be able to move with the doors open.
We've instituted some procedural changes (e.g., check-lists for opening
the telescope), that should make this kind of accident less likely.
We will have a external audited safety review for the observatory
later in the year, jointly with the SDSS.
Last month's minutes are approved.
Next meeting: May 10, 12 noon.
Appendix: (slightly edited) E-mail from Alan Uomoto about the status
of the Secondary:
Jim Burge reports that SOML needs to make one
more measurement: locating the exact position
of the optical center of the mirror. A final
report will be delivered in about two weeks.
I asked Jim to translate the mirror measurements
into psf and/or encircled energy plots so we could
get an idea of on-the-sky performance. He said he
would and expected that our combination of primary
and secondary would give us images far smaller than
the seeing.
The optical test setup will be dismantled shortly
(~a couple of weeks) so if we want to test after
installing a mounting part it would have to be done
soon. It will also have to be scheduled through
the SOML office since it requires removing the mirror
from the cell to install the part and then reinstalling
the mirror, a big task.
Alan Uomoto
April 12, 1999
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