An IR spatial interferometer at 10 μm wavelength and measurement of stellar dust shells

Abstract The University of California Infrared Spatial Interferometer (ISI) for the 10 μm wavelength region is briefly described and results obtained on 13 prominent stars and on atmospheric phenomena are discussed. The interferometer has two movable telescopes of 1.65 m aperture and operates in principle like a modern radio interferometer, using heterodyne detection, CO 2 laser local oscillators, RF delay lines, and lobe rotation to maintain a fixed-frequency fringe rate. Extensive measurements have been made on atmospheric pathlength or phase fluctuation characteristics. These show substantial deviations from the Kolmogorov-Taylor model, fortunately in a direction favoring adaptive optics, long baselines, and the use of infrared wavelengths. Outer scales as small as about 10m occur under good seeing conditions. Visibility results on the 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 between emissions of a number of decades. Other stars also vary with time, but are characterized by cyclic variations typical of long-term variables and more continuous emission with dust formation near the stars at temperatures as high as 1300K.