Subject: 3.5-meter telescope status


Submitted: Wed, 22 Nov 1995 14:40:42 -0700

Message number: 25 (previous: 24, next: 26 up: Index)

>Hi Bruce,
>Sorry to bother you, but several people
>have asked me recently about the ARC engineering.
>Specifically, what has been done to the telescope,
>what has changed, will it effect my observing?
>I notice that the ARC starts scientific work
>on Monday and I observe next saturday.
>Could you summaries the changes to ARC during
>this last engineering time? I'll then circulate
>this to all the UC people.

Dear Bob:

I apologize for not doing a better job of keeping the users posted on the
3.5-m shutdown activities, which has been due in part to demands of getting
materials ready for the ARC annual Board of Governor's Meeting.  I've
shared some of the shutdown information with Lew Hobbs and other members of
the 3.5-m User's Committee last week, but enough has happened since then to
merit an update in the areas which impinge on observational performance.
I'm also posting this on the general APO mail exploder at Princeton for a
more general distribution. The effect of changes on upcoming observing
programs is slightly in flux at the moment, and users should check with us
the day before their runs to get the current story.

A major portion of the shutdown work was to essentially rebuild the azimuth
drives, a task which is expected to improve pointing/tracking and give us
better reliability of the drive--the results are yet to be determined.
This work will be largely transparent to the users except over the long
haul, as the drives were working pretty well the month prior to the
shutdown, in spite of their known faults.  Getting the drives put back
together was delayed to the last week of the shutdown, and there's some
residual tuning still ongoing.  We don't yet have a good pointing model for
the telescope, and blind pointing is off by 10s of arc seconds and tracking
is only decent for a few minutes.  Ed Turner has given me license to
pre-empt the telescope tonight to get a good pointing model, so this may
not be a problem much longer.

The big-chip guider camera shutter failed last weekend, and we have
replaced the camera with a smaller (512^2) chip backup.  This camera is
much more sensitive than the other one (which is going back to
SpectraSource for repair).  The spare camera guides on ~17th magnitude
objects, and so far we have found that roughly half of the random field
pointings contain usable guide stars.  Eric Deutsch at UWashington has
developed a guide star finding utility which is accessed from the APO web
server under instrument/guide camera.  The guider is not yet completely
usable through the remote interface, but our Observing Specialists have
been able to use it to support science observations these past couple of
days. We need to use the guider to learn more about its capabilities and
limitations.  Recommendation:  try the guider, especially if your exposure
times are more than a few minutes!

We also changed the spectral and flat-field calibration lamp set-up so that
the lamps shine downward onto the primary mirror cover, which is now closed
during calibration exposures.  The main advantage is that the uniformity of
flat-fielding is expected to be a bit better, and less time is wasted
during calibrations because now we don't have to close/open cycle the
enclosure doors to do wavelength and flat-field calibrations.  More
automation and flexibility to these systems will be added shortly, and the
ease and accuracy of calibrations will continue to be improved.  For now,
realize that exposure times for flats and wavelength calibrations may be
slightly different (shorter?) than before--ask the Observing Specialists
for the latest information.

There were a lot of other shutdown activities, most having limited user
visibility (e.g., enclosure wheel repair, redistribution of UPS power,
etc.)  One item to mention is that the Drift Scan Camera went to Fermi Lab
for repairs and is expected back at APO by the end of November.  We will
post updates on how its performance has changed when we have solid

There is a new version of Remark (2.3.4) which you should be using if
you're  observing remotely.  Also, the operating system of the MC was
upgraded to the current version of Solaris.

It'll take a little while for the operations to settle down again, so I
strongly recommend contacting us before your observing runs to keep abreast
of changes and current conditions.

best regards

Bruce Gillespie

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