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The Cryogenic Optical Bench: A Multifunction IR...(1Sep93)
Camera for Kitt Peak
(from KPNO, NOAO Newsletter No. 35, 1 September 1993)

The Cryogenic Optical Bench (COB) is a 1-5 micron IR camera with
multiple cold spectral and spatial filtering capabilities. These can be
combined and reconfigured while observing to adapt the instrument to a
variety of functions. It is available for "shared risk" observing at
the 1.3-m, 2.1-m, and 4-m in spring semester 1994.

COB currently uses a 256 x 256 InSb array from Santa Barbara Research
Center. Pixel scale is 0.9 arcsec at the 1.3-m, 0.5 at the 2.1-m, and
0.3 at the 4-m. Operating modes at present are:

o   Broadband imaging at 1.0 micron, J, H, K, and K' (2.0-2.3 microns);

o   Narrowband imaging at 1-4 microns, including 1-2% filters at 1.08, 1.25,
    1.28, 1.64, 1.99, 2.12, 2.16, 2.22 (4%), 2.36, 2.38, 3.08, 3.30, 3.35,
    3.40, 4.00, 4.05 microns;

o   Polarimetry in broadband filters and two micron narrowband filters;

o   Imaging at resolution ~500 in the two micron window using a tunable
    Fabry-Perot and the narrowband filters as order sorters;

o   Occultation of a central bright source for imaging and polarimetry, with
    a variety of focal plane spots;

o   Long slit spectroscopy at resolution ~300 in the J, H, and K bands with
    a grism and focal plane slit;

o   Polarimetry with the grism at J, H, and K.

We have used the instrument extensively in several of these modes at
the 1.3-m and are quite pleased with its performance. This includes
imaging in the various modes and spectroscopy in the two micron window.
We have operated with the three micron narrowband filters during the
daytime in May; this was quite practicable, and we are eager to see
what background conditions will be in the winter.  However, there are
combinations which have not been "turned on" at the telescope, and so
we have no practical experience to share in these modes. It is not yet
possible to operate in broadband L, and we are working on the speed and
well depth issues involved for operation beyond three microns with wide
bandpasses. We are also continuing to broaden the filter inventory.

As a rough guide to performance, dark current and read noise are at
levels permitting background limited operation in all filter
combinations. The background limit is reached comfortably in seconds to
tens of seconds in the broadband filters, tens to hundreds of seconds
in the narrowband filters, about three minutes with the Fabry-Perot or
grism, and about 50 milliseconds in the three micron filters.  Data
taking modes include multiple readout, to reduce read noise in low
background configurations, and fast coadding, to avoid a data deluge at
high backgrounds. Observer interface is via a workstation with easy
access to the data within IRAF for real-time reduction and analysis.

We emphasize that while the spectroscopic mode has great utility, COB
is not a spectrometer. The resolution is fixed at a modest value, and
there is no spectroscopic capability beyond 2.5 microns. Purely
spectroscopic proposals will be better served by CRSP in its new,
large-format configuration.

In general, "shared risk" implies that every reasonable effort will be
made to provide an instrument which meets its performance goals. It may
require more hands-on operation, and be less user friendly, than a
fully commissioned facility instrument. Unforeseen problems may require
the observer to downscale significantly the program objectives or
switch to an alternative program or backup instrument. With COB in
particular, technically challenging proposals may have backup modes
utilizing a reconfiguration of the instrument.  For example, narrowband
imaging can be accomplished by use of the Fabry-Perot, by long slit
mapping with the grism, or with fixed filters, with tradeoffs in
spectral resolution, sensitivity, and integration time. In addition to
scientific issues, shared risk proposals should address how the
observations will aid in defining instrument performance and operating
protocols.

Prospective proposers are encouraged to contact Ron Probst, Mike
Merrill, or Ian Gatley (e-mail:  lastname@noao.edu) for more detailed
discussion prior to proposal submission. See also the following
articles for comments on choice of appropriate instrument.

Ron Probst for the infrared group

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