AN IR SPATIAL INTERFEROMETER AT 10-MU-M WAVELENGTH AND MEASUREMENT OFSTELLAR DUST SHELLS

The University of California Infrared Spatial Interferometer (ISI) for the 10 mum wavelength region is briefly described and results obtaine d on 13 prominent stars and on atmospheric phenomena are discussed. Th e interferometer has two movable telescopes of 1.65 m aperture and ope rates in principle like a modern radio interferometer, using heterodyn e detection, CO2 laser local oscillators, RF delay lines, and lobe rot ation to maintain a fixed-frequency fringe rate. Extensive measurement s have been made on atmospheric pathlength or phase fluctuation charac teristics. These show substantial deviations from the Kolmogorov-Taylo r model, fortunately in a direction favoring adaptive optics, long bas elines, and the use of infrared wavelengths. Outer scales as small as about 10 m occur under good seeing conditions. Visibility results on t he 13 stars show that six of them have dust shells rather far from the star and provide evidence for episodic emission of gas with times bet ween emissions of a number of decades. Other stars also vary with time , but are characterized by cyclic variations typical of long-term vari ables and more continuous emission with dust formation near the stars at temperatures as high as 1300 K.