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B. F. Lane (Caltech), M. M. Colavita (JPL)
We discuss implementation and testing of phase referencing at the Palomar Testbed Interferometer. The implementation uses an isoplanatic phase reference with separate primary and secondary beam combiners, linked with laser metrology. Preliminary work has achieved a coherent integration time of 250 ms, compared with 10-20 ms for the ordinary bright star mode. Observations have been made of several visual binaries, including 16 Cyg AB (mk = 4.5 and 4.6, resp.) which demonstrate that phase-referenced visibility measurements can be calibrated at the level of 2 - 7%