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====== Palomar Testbed Interferometer ([[http://pti.jpl.nasa.gov/|PTI]]) ======
\\  PTI measured the rotationally induced oblateness of the **rapidly rotating star Altair**, finding major and minor axes of 3.46 ± 0.04 and 3.04 ± 0.07 mas. The value of //v// sin //i// was determined independently of spectroscopic techniques.\\ \\  Differential “dual-star” **astrometric measurements of the nearby binary 61 Cygni AB** achieved a 170 µas precision over a 45-day timescale, yielding proper motions of the components in excellent agreement with the HIPPARCOS determination of system motion.\\ \\  Combined with radial velocities, **Cepheid angular diameters** allow determination of the stars’ distances and hence a check on this important link to the cosmic distance scale. PTI measured the change in angular size of the Cepheid ζ Gem, deriving a distance of 362 ± 38 pc.\\ \\ \\ 
===== Palomar Testbed Interferometer =====
\\  The Palomar Testbed Interferometer is a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was developed primarily to demonstrate the utility of ground-based differential astrometry in the search for planets around nearby stars, and to develop key technologies for the Keck Interferometer and space-based missions.\\ \\  PTI's dual-star tracking system, the first and (still) only of its kind, simultaneously tracks interference fringes from a target star and a\\  reference star against which the target is measured. The current operating modes of PTI are visibility amplitude and narrow-angle\\  astrometry through fringe scanning.\\ \\  The Michelson Science Center (MSC) currently adminsters scientific operations at PTI on behalf of the PTI collaboration, with funding from the MSC, the SIM-PlanetQuest mission, the PHASES project and the Infrared Processing and Analysis Center. PTI is a testbed for the engineering, techniques, operations, and data reduction for the Keck Interferometer. Data from the visibility mode are made available to the public after 18 months.\\ \\  Publications: [[http://msc.caltech.edu/missions/Palomar/publications.html|http://msc.caltech.edu/mission s/Palomar/publications.html]]\\  Data archive and support: [[http://msc.caltech.edu/software/PTISupport/|http://msc.caltech.edu/softwar e/PTISupport/]]