Near-infrared guiding and tip-tilt correction for the UC Berkeley Infrared Spatial Interferometer

The UC Berkeley Infrared Spatial Interferometer (ISI) is a heterodyne stellar interferometer which operates in the mid-infrared between 9 and 12 microns. This wavelength range makes the ISI particularly well-suited to high resolution study of late-type stars and other objects surrounded by relatively cool dust, the emission from which peaks in the mid-infrared. Unfortunately, this same dust tends to reduce the amount of visible light available from the sources, making many interesting infrared objects too faint for the original telescope guiding system, which used a silicon CCD camera. This system has been replaced by a guiding and tip-tilt correction system based on an InSb infrared camera and a fast, controllable tilting mount for one of the mirrors in the signal path. The new system has improved the quality of ISI fringe visibility data on bright sources and allowed the study of previously inaccessible objects.