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Important Changes to CRSP (1Mar93)
(from KPNO, NOAO Newsletter No. 33, 1 March 1993)

Some observers will have already noted that CRSP (our IR Cryogenic
Spectrometer) has received the detector that was formerly in IRIM,
significantly improving the operation of the instrument (far better
cosmetics, no flux memory). However, we do not plan to stop there. Two
major upgrades are planned for the summer of 1993:

1.  The Digital Control Unit will be modified to operate with a SPARC
host computer, similar to the FIRE program used with SQIID. This should
free us from the three-headed albatross (DEC 11/73, Grinnell, and
Getpix) which has become less and less reliable with time.

2.  The detector will be replaced with a 256 x 256 SBRC InSb detector
with 30 um pixels. Although the array intended for CRSP has only 170
operable rows, this should have no adverse effect on the instrument,
since the slit will illuminate only 135 rows. We expect this to be a
very significant step. The new SBRC arrays are far superior to their
predecessors in many respects (good cosmetics, dark current ~ 1 e-/s,
single-read noise <  30 e-) which are important to spectroscopy. In
addition, the smaller pixels will permit full sampling of the slit,
even under good seeing conditions, as well as enhanced spatial
resolution on extended sources.  The smaller well capacity may limit
operation at long wavelengths and low resolution, depending on the
minimum readout time we can achieve.

Since the new array will be approximately 60 percent larger in the
dispersion axis, we expect increased free spectral range with the high
dispersion gratings. At this point, we cannot say how much additional
useful spectral coverage will result, as this depends on the effects of
vignetting and aberrations at the edge of the camera optics. Until we
have experience with the upgraded instrument, prospective observers
should use the present performance as a guideline.

The planned upgrade will require significant time and effort. Since
CRSP is scheduled to mid-July in the present semester, the physical
modifications to the instrument and electronics cannot begin until
then. We anticipate the instrument will be available for scheduled use
by 1 November, although prospective users are warned that the
performance and operating procedures may not be fully characterized by
that time.

Dick Joyce

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