ASTRONOMICAL FOURIER-TRANSFORM SPECTROSCOPY OF THE 1990S

The number of FT spectrometers mounted behind optical telescopes has d ecreased with the development of modern cold-grating infrared spectrom eters, the instruments of choice for the study of faint astronomical o bjects. However, Fourier-transform spectroscopy remains unrivalled for high resolution work in the infrared. The instrument in operation beh ind the Canada-France-Hawaii telescope is presented. The sources commo nly under study, strong infrared sources, are those objects of the sol ar system with an atmosphere (planets and satellites) and various type s of stars. Of particular interest are the late-type stars surrounded by cold circumstellar envelopes or very young objects embedded in thei r parent molecular clouds. The latter sources are used to probe the in terior of giant molecular complexes. The astronomical sources offer co nditions difficult to obtain in the laboratory. The most significant r esults obtained with an FT spectrometer in the last few years include the detection of the molecular ion H-3(+) on Jupiter and the radical C -5 in the carbon-rich envelope of the evolved star IRC + 10216. Result s will be also mentioned from the millimetric range, a new window of e xploration from the ground, where FT spectrometers are starting to be used, to benefit from their broad spectral coverage. New applications have also been tested. For example, with the development of 2-D infrar ed arrays, spectro-imaging becomes possible and an imaging FT spectrom eter is in operation behind the Canada-France-Hawaii telescope. In ano ther field, an FT spectrometer is used as seismometer to detect the ac oustic oscillation spectrum of giant planets. The next challenge for F ourier-transform spectroscopy is the era of new technology telescopes. The possibilities of an FT spectrometer behind an 8-m class telescope will serve as a conclusion.