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M. M. Colavita (JPL)
The Palomar Testbed Interferometer (PTI) is a long baseline near-IR interferometer developed by JPL for NASA and installed at Palomar Observatory; first fringes were obtained in 1995. PTI serves as a testbed for other interferometer projects, especially the Keck Interferometer. PTI is capable of high accuracy fringe amplitude measurements at H and K using active fringe tracking over its 110-m baseline. Good visibilities are routinely obtained on sources as faint as 5.5 mK, with visibility calibration accuracies of 1.5-2% on brighter sources. The instrument is highly automated, and up to 100 130-sec scans per night are possible, allowing efficient pursuit of "amplitude" science on single and binary stars, and driving the development of automated planning, analysis, and archiving tools. PTI also incorporates a dual-star capability to enable high accuracy narrow-angle differential astrometry. From measurements of a bright visual binary, short-term precisions which correspond to a noise floor of less than 50 uas in an hour have been achieved, along with night-to-night positional repeatability of 100 uas over a 7-night run.