Mid-infrared interferometry on spectral lines: I. Instrumentation

The U. C. Berkeley Infrared Spatial Interferometer has been outfitted with a filterbank system to allow interferometric observations of mid-infrared spectral lines with very high spectral resolution (R ~ 10^5). This paper describes the design, implementation, and performance of the matched 32-channel filterbank modules, and new spectral line observations of Mars and IRC+10216 are used to demonstrate their scientific capability. In addition, observing strategies are discussed for accurate calibration of fringe visibilities in spectral lines, despite strong atmospheric fluctuations encountered in the infrared.