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UKIRT Annual Report 1995 and 1996
THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1995 AND 1996
2. Scientific Results during 1995 and 1996
2.2. Selected Scientific Results
2.2.7. CGS3 and Spectral Irradiance Calibration in the Infrared
M. Cohen (University of California, Berkeley)
and J.K. Davies (JAC)
CGS3, a 10-20 m spectrometer, is the
oldest instrument in UKIRT's
current suite but is still productive, largely in front-line
scientific studies of asteroids, comets, circumstellar and interstellar
dust, ionised nebula, and even distant galaxies. However, CGS3 also
continues to play a crucial role in providing one of the fundamental needs
of observational astronomers, absolutely calibrated continuous
spectra. A set of accurate flux standards forms the basis for all flux
calibrations and thus is linked to almost every astronomical measurement.
Cohen & Davies (1995) described the role played by CGS3
in the generation of new absolute spectra for  Dra
and  Boo that support the calibration
of instruments on ISO,
notably the SWS (Cohen et al. 1996). It is noteworthy that  Dra
has become a primary reference for the SWS and has been observed by other ISO
instruments such as CAM and PHOT. Further, this star was observed on
the MSX satellite (Mill et al. 1994) expressly for comparison with
 Boo and  CMa. We are confident that the measurements by
several satellite-borne instruments can be tied together using these
absolute spectra and acknowledge the part played by UKIRT/CGS3 in
contributing high signal-to-noise 10 and 20  m spectra to this
overall programme.
We have continued to collect CGS3 10 (and sometimes 20)  m spectra of
late-G to early-M giants to flesh out the grid of spectral types
investigated by Cohen & Davies and to supplement Kuiper Airborne
Observatory (KAO) spectra of the same archetypal stars in order to create
continuous 1-35 m spectra. During
the period mid-1994 to mid-1997
we have obtained new 10 m CGS3 data
for 24 stars, and new 20 m
data for five stars. These are archived as ratios to the spectrum of an
established calibrator, such as 
CMa,
at a very closely matching airmass. With the aid of CGS3, there now exist
composites (observed spectra)
for giants of type K0, K1.5, K3, K5, M0, M1.5 and M2.5. This subset of
types will
be utilised in 1998 to create up to 350 absolutely calibrated stellar
spectra using the concept of stellar templates (Cohen et al. 1998).
MC thanks NASA-Ames for support of this study under cooperative
agreement NCC 2-142 with UC Berkeley, using funds provided by Dr S. D. Price
of US Air Force Phillips Laboratory. We thank the UKIRT Service Program
for providing many of the excellent CGS3 spectra as well as the PATT for
their awards of telescope time.
References
Cohen, M. & Davies, J. K. 1995, MNRAS, 276, 715
Cohen, M., et al. 1987, in preparation
Cohen, M., et al. 1996, AJ, 112, 2274
Mill, J. et al. 1994, Spacecraft & Rockets, 31, 900
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