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IR News (1Sep93)
(from CTIO, NOAO Newsletter No. 35, 1 September 1993)

This issue we have a lot of news regarding the IR instrumentation.
Major changes are (finally) taking place in what we can offer our
users--read the following articles carefully to understand your
options.

OSIRIS Continues

CTIO has reached an agreement with the Ohio State University to extend
the visit of the Ohio State Infrared Imaging Spectrometer (OSIRIS)
through the first nine months of 1994. This amounts to all of first
semester and roughly the first two months of the second semester.
OSIRIS has now actually been used successfully on the 4-m telescope,
and we expect it to work satisfactorily for visitors as well.

The terms of the agreement are slightly different than for the current
second semester (1993). There are two aspects that are of general
interest. First of all, CTIO personnel will be assuming greater
responsibility for support of the instrument. This means specifically
that CTIO scientific staff or observer support people will be providing
visitor checkout, and also that the mountain electronics crew will have
been trained to diagnose and repair (by board swapping) any failures
that may occur. Support for major failures will continue to be provided
by OSU; while this means in principle that a night or more could be
lost, the history of the instrument at Flagstaff suggests that this is
unlikely.

The other new condition of the agreement is that OSU has been
guaranteed three weeks of time on the 1.5-m telescope with the
instrument, primarily during the first semester. The time will be used
to carry out an NSF-funded galaxy survey. It is our opinion that the
increased opportunities for other observers - both on the 4-m and on
the 1.5-m - more than justify the terms of the agreement. OSU will
provide a written description of the program of observations to be
carried out, which will be reviewed by the CTIO staff.

One other detail that affects users is that optimum use of OSIRIS
requires installation of a cold Lyot stop designed for the specific
telescope. In order to minimize such installation work, the instrument
will be scheduled on the same telescope during several consecutive
light runs. Tentatively, we expect that it will start the semester on
the 1.5-m (where it will have been used since December) and will shift
over to the 4-m around mid-semester (probably May or June; this will
depend on demand) and will likely remain there until it returns to the
US. We may be able to obtain some flexibility by using it on the 1.5-m
with the 4-m Lyot stop, since the performance reduction in this
configuration is modest, but users are warned that it may be difficult
or impossible to schedule proposals with tight date restrictions.

OSIRIS Performance Update

OSIRIS has now had its first run on the 4-m, scheduled as a visitor
instrument. Set-up and operation went fairly smoothly, with only one
minor failure. Furthermore, there were several clear nights, so that we
have actual sensitivity measurements:

On the 4-m, in 10 minutes one can detect (5-sigma) stars of K=18.5 to
19. H sensitivity will be slightly better, and J sensitivity perhaps
half a magnitude better again. Although a K' filter is present, there
is very limited experience with it. Because the OSIRIS cold stop has
been carefully matched to the telescope, it is not clear that the K'
filter offers significant gains in sensitivity.

The cross-dispersed option has also been exercised.  This provides
simultaneous JHK spectra at low resolution. The low limit is set by the
blocking filter, which is required to avoid problems with the grism
second order in the K band; the lower limit is approximately 1.18
microns. For shorter wavelength work, one can use a 0.9-1.1-micron
filter, although spectral coverage is again limited by the free
spectral range of the OSIRIS grating, which is blazed for 6.6 microns.

Unlike the CTIO instruments, there is no dichroic in OSIRIS. The only
way to guide therefore (other than trusting the telescope tracking) is
with the offset guider. As used with OSIRIS, the field of view of the
TV camera is very small (5 arcsec); this makes searching for guide
stars very slow. Anyone with OSIRIS time is strongly advised to come
with accurate (1 arcsec or so) offsets to guide stars!

IR Imagers Out of Service

Because of the continued availability of OSIRIS, we are able to take
our other IR imagers out of service, as they provide smaller formats or
reduced efficiency. As of this writing, the 58 x 62 IR Imager and the
Pt:Si Imager are no longer available. This policy does mean that L-band
imaging is no longer possible at CTIO--although L-band photometry is,
with similar efficiency, using the single-channel photometer. We will,
reluctantly, provide the Imager for anyone with a continuing program
who requires L-band images, and who provides a justification for the
need acceptable to the TAC.

Work on CTIO's HgCdTe Imager has now progressed far enough for us to
lay out a plausible schedule for completion. It is currently our
expectation that the instrument will be completed around the middle of
first semester, and that it will be fully commissioned by the start of
second semester 1994. Watch the March 1994 Newsletter for further
details.

IR Spectrometer to be Upgraded

We are also taking advantage of the OSIRIS visit to upgrade the CTIO IR
Spectrometer to use a 256 x 256 InSb array. The existing optics should
provide acceptable performance for a larger array with smaller pixels,
although we will continue to have only a relatively short length of
usable slit. This upgrade is being done cooperatively with KPNO, who
will produce a copy of the WILDFIRE control electronics to run the 256 x
256 array, and will assist with the array installation.

This upgrade requires relatively little CTIO manpower, but the people
involved are largely the same as for the HgCdTe Imager, and hence final
commissioning of the upgraded instrument will not occur until after the
Imager has been commissioned.  It is likely that the upgraded IRS will
not be available until about the time OSIRIS leaves--i.e.  second half
of second semester 1994. The IRS will not be available in any form
first semester because of the upgrade.

IR Photometer Lives

We will continue to offer single-channel IR photometry on the 1.5-m and
4-m telescopes, with both the InSb detector (D-3) and bolometer (D-1).
For work at longer wavelengths, this is the only southern hemisphere
facility open to US astronomers, and we do not plan to remove it from
service at any time in the near future. In fact, in order to eliminate
our dependence on the aging Data General computers currently used for
the system, we intend to convert to a PC-based data acquisition system
in the next year or so.

J. Elias, R. Elston, B. Gregory

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