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2. THEORETICAL FITS TO ASTRONOMICAL SPECTRA
This brings up a second point that clearly emerged at this meeting. Theorists,
who for decades
have been predicting the shapes of infrared spectra expected from a wide variety
of
astronomical sources, now are also suddenly able to verify the great power of
their techniques.
Therèse Encrenaz showed us a model spectrum of Saturn that included
phosphene
PH 
, arsene AsH , ammonia NH , deuterated methane CH D, and a slight
trace of water vapor H 
O. Were it not for the spectacularly good fit that all
the other
constituents provide to the spectrum of Saturn observed with ISO across the
entire near and
mid-infrared, the small differences made by the traces of water vapor would
never have been
noticed. Thanks to the theoretical fits, however, H O is clearly detected. We
are now
asking whether the water originates in infall of material from the Saturnian
rings or possibly
signifies other sources.
Excellent theoretical fits were also evident in the simulation of stars with static atmospheres. Such model atmospheres require detailed understanding of the spectral frequencies and transition probabilities of huge lists of spectral lines of atoms, radicals, molecules, their isotopes, and their ions. Robert Kurucz told us he uses 58 million lines to fit his model atmospheres. In turn, Christoffel Waelkens showed us how essential high-quality fits are for precise calibrations of ISO's short wavelength spectrometer, SWS.
Martin Harwit