Infrared Fourier spectrometer for laboratory use and for astronomical studies from aircraft and ground-based telescopes

Evaluation of an InSb infrared detector at liquid N(2) and liquid He temperatures

The performance of an InSb infrared detector has been evaluated at liquid nitrogen and liquid helium cryogenic temperatures. A significant improvement in sensitivity was observed when the detection system was Johnson noise limited. With 300-K background radiation and diffraction limited throughout, the NEP of the detector is 1.5 x 10(-16) W Hz(-(1/2)) at 1.65 microm. Potential improvement is expected especially for astro-physical observations which are made in lower photon background conditions.

Infrared Fourier spectrometer for airborne and ground-based astronomy

A unique high resolving power near-infrared, astronomical Fourier spectrometer has been constructed foruse at both ground-based and airborne telescopes. Its capabilities include a limiting resolution of 0.01 cm(-1) and spectral coverage over the InSb detector sensitivity region (0.8-5.6 microm). The instrument is optimized for operation in environments inaccessible to other high-resolution Fourier spectrometers, namely, the Cassegrain focuses of conventional telescopes and the NASA Kuiper Airborne Observatory's 91-cm telescope. Details of the spectrometer are discussed, and various astronomical and laboratory spectra are presented.

Deuterated Methane Observed on Saturn

Absorptions for the V(2) band of deuterated methane (CH(3)D) have been observed in the 5-micron spectrum of Saturn, obtained with a Fourier transform spectrometer. Analysis of the band yields a CH(3)D abundance of 2.6 +/- 0.8 centimeter-amagat and a temperature of 175 +/- 30 K for the mean level of spectroscopic line formation. This temperature indicates that a substantial portion of Saturn's flux at 5 microns is due to thermal radiation, and that we are therefore looking fairly deep into its atmosphere, as is the case for the Jupiter 5-micron window. This CH(3)D abundance leads to a deuteriumlhydrogen ratio of about 2 x 10(-5) in Saturn's atmosphere. This ratio is much lower than the terrestrial value but comparable to that determined for Jupiter and may be taken as representative of the deuteriumlhydrogen ratio in the solar system at the time of its formation.

Airborne infrared astronomical observations by Fourier transform spectroscopy

Infrared spectroscopic observations from NASA-operated aircraft constitute a rapidly maturing application of FTS methods initially developed for ground-based telescopes. Coupled to airborne telescopes up to 36 in. in diameter, these experiments are now producing new astronomical results as exciting and unexpected as those derived from Connes's first high resolution planetary observations at mountain-top observatories. This review examines the special problems of the ir spectral region that led to aircraft observatories and includes a brief survey of the facilities themselves and their modes of operation. The special problems of operating FTS devices on aircraft and the scientific results achieved with current capabilities are discussed. Finally, airborne observations are compared to the ultimate in high-altitude observing platforms: earth-orbiting cooled and uncooled telescopes carried by the space shuttle vehicle.

Near infrared astronomical light collector

A 4-m aperture light collector has been built using the mosaic principle specifically for high resolution stellar spectroscopy in the near infrared by the Fourier multiplex technique. The most novel feature is complete servo control of all optical elements to bring individual images to a common point. Initial goals were a spectral survey of ir objects, and the testing of techniques for a larger future collector. However, the project has been stopped by lack of interest and support; the finished collector will not be used.