Subject: Availability of DIS gratings

From: Russet McMillan

Submitted: Thu, 26 Sep 2002 20:04:08 -0600 (MDT)

Message number: 614 (previous: 613, next: 615 up: Index)


As you may already be aware, recent DIS throughput measurements
indicate that there is a very real difference in throughput between
the medium-resolution red grating and the low-resolution red grating.
However, the extreme wavelength range of the low-resolution grating
still leaves much of the chip unused.  Therefore we will be sticking
with the "default" setups that were established when DIS II was
checked out last spring: high/high in one bay, and blue low/red medium
in the other bay.

You may still request another pair of gratings (one blue, one red) if
important for your science, but please be sure to notify us of your
request at least a few days in advance of your run.  If your request
conflicts with the program of another observer on the same night who
wants one of the default setups, you will have to sacrifice half an
hour per grating (one hour for a grating pair) to allow them to be
changed in the middle of the night.  Last-minute requests may also
incur a time penalty, or may be refused.

Please do NOT assume that your proposal constitutes sufficient warning
that you want a non-default setup.  The inconsistencies in filling out
the proposal form that were discussed recently by Ed Turner also cause
us some confusion about DIS grating requests.  So we will continue to
assume that you will be using one of the default pairs, unless we are
explicitly informed otherwise by email to .

This is the same policy that was articulated in more detail in
apo35-general message 563 and has been in practice since then.  The
only difference is that in March we were anticipating that we would
eventually be able to retire some gratings, whereas now it appears
that there are continuing reasons for some programs to require
non-default sets.

Plots of the throughput results are available on Jon Holtzman's pages: 

>  You can see the relative throughput plot at:
>  and the absolute plot at

Thanks for the cooperation you've all given us in the past few months
while we tried to work out a reasonable policy!

			     Russet McMillan.

APO APO APO APO APO  Apache Point Observatory 3.5m  APO APO APO
APO  This is message 614 in the apo35-general archive. You can find
APO  the archive on
APO  To join/leave the list, send mail to
APO  To post a message, mail it to