The Berkeley Infrared Spatial Interferometer is a unique system of three 1.65-meter telescopes located at the Mt. Wilson Observatory. Its baselines range from 4 to approximately 75 meters and it is capable of 20 milliarcsecond resolution. The system uses heterodyne detection with a bandwidth of 0.2/cm and the resulting signals can be filters to obtain arbitrarily narrow spectral widths. The recent addition of a third telescope has allowed phase closure measurements to an accuracy of 1 degree, which allows nearly complete Fourier analysis of intensity patterns, including asymmetries. An observing program of evolved late-type stars will be continued using the interferometer. The sizes of such stars and select associated features (surrounding dust distributions and asymmetries, water vapor envelopes, etc.) will be directly measured. The narrow bandwidth capability will allow the atomic and molecular spectral lines of surrounding gas to be avoided or selected yielding, among other characteristics, reliable and realistic stellar sizes. The observations will follow the changes in size of prominent Mira variable stars as a function of phase and examine possible departures from sphericity of Miras and red giants. Previous studies with the interferometer have shown movements of dust clouds surrounding late-type stars as well as deviations of the clouds from spherical symmetry. Studies of these variations will be continued to provide information on the motion of dust clouds around stars, and from this and Doppler measurements, also a determination of distances. The work here will provide training for young scientists (a postdoctoral research associate) and students (2 graduate students as well as undergraduates) who will have hands-on opportunities to learn optics, electronics, computer control systems, data analysis, and scientific interpretation. Interferometry and instrumentation are two areas of high priority for the astronomical community and the education of the next generation of instrument builders is critical the field's continued success.
