University of California/Berkeley Infrared Spatial Interferometer: recent system upgrades and analysis of atmospheric fluctuations

Abstract
Recently, a number of technical improvements in the Infrared Spatial Interferometer (ISI) helped to increase the signal-to- noise ratio in fringe power by about a factor of two over the previously reported factor of 10. The improvements comprise higher quantum efficiency and larger bandwidth HgCdTe heterodyne detectors, better IF signal processing components, new lock-in amplifiers, a fringe calibration system and an enhanced autoguider. A comprehensive effort to characterize and improve the short-term and long-term stability of the infrared detection system led to a large improvement of the calibration of visibility data. The ISI has been used on baselines of 10- and 32-m length during the last observing season. Fringes were obtained on 8 sources on the 32-m baseline so far. This paper described recent system upgrades and a new filter bank for spectroscopy on molecular lines, as well as some more studies of atmospheric fluctuations. Results of our astrophysics and astrometry programs are reported in the following three papers.

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