The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interf erometer located at Palomar Observatory, California. It was built as a test bed for interferometric techniques applicable to the Keck Interferometer. F irst fringes were obtained in 1995 July. PTI implements a dual-star archite cture, tracking two stars simultaneously for phase referencing and narrow-a ngle astrometry. The three fixed 40 cm apertures can be combined pairwise t o provide baselines to 110 m. The interferometer actively tracks the white- light fringe using an array detector at 2.2 mu m and active delay lines wit h a range of +/-38 m. Laser metrology of the delay lines allows for servo c ontrol, and laser metrology of the complete optical path enables narrow-ang le astrometric measurements. The instrument is highly automated, using a mu ltiprocessing computer system for instrument control and sequencing.