Palomar+Testbed+Interferometer+(PTI

== = = =Palomar Testbed Interferometer ([|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/mission s/Palomar/publications.html] Data archive and support: [|http://msc.caltech.edu/softwar e/PTISupport/]