PRECISION MEASUREMENT OF STELLAR SIZES AND CIRCUMSTELLAR MATERIAL WITH 10 MICRON INTERFEROMETRY AND NARROW FREQUENCY BANDWIDTHS

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ABSTRACTThe Berkeley Infrared Spatial Interferometer is a unique system of three 1.65-metertelescopes located at the Mt. Wilson Observatory. Its baselines range from 4 toapproximately 75 meters and it is capable of 20 milliarcsecond resolution. The systemuses heterodyne detection with a bandwidth of 0.2/cm and the resulting signals can befilters to obtain arbitrarily narrow spectral widths. The recent addition of a third telescopehas allowed phase closure measurements to an accuracy of 1 degree, which allows nearlycomplete Fourier analysis of intensity patterns, including asymmetries.An observing program of evolved late-type stars will be continued using theinterferometer. The sizes of such stars and select associated features (surrounding dustdistributions and asymmetries, water vapor envelopes, etc.) will be directly measured.The narrow bandwidth capability will allow the atomic and molecular spectral lines ofsurrounding gas to be avoided or selected yielding, among other characteristics, reliableand realistic stellar sizes. The observations will follow the changes in size of prominentMira variable stars as a function of phase and examine possible departures fromsphericity of Miras and red giants. Previous studies with the interferometer have shownmovements of dust clouds surrounding late-type stars as well as deviations of the cloudsfrom spherical symmetry. Studies of these variations will be continued to provideinformation on the motion of dust clouds around stars, and from this and Dopplermeasurements, also a determination of distances.The work here will provide training for young scientists (a postdoctoral researchassociate) and students (2 graduate students as well as undergraduates) who will havehands-on opportunities to learn optics, electronics, computer control systems, dataanalysis, and scientific interpretation. Interferometry and instrumentation are two areas ofhigh priority for the astronomical community and the education of the next generation ofinstrument builders is critical the field's continued success.