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Palomar Testbed Interferometer (PTI) Support Page

The Palomar Testbed Interferometer (PTI) was a near-infrared, long-baseline stellar interferometer located at Palomar Observatory in California. First fringes were obtained in July 1995 and it was operational until December 2008.

PTI's development and early operations were carried out by the Jet Propulsion Laboratory (JPL) with funding from NASA under its TOPS, ASEPS (Astronomical Studies of Extrasolar Planetary Systems), and Origins programs, with additional funding from the JPL Director's Discretionary Fund and the JPL Director's Research and Development Fund. Subsequent science operations were carried out by the NASA Exoplanet Science Institute (NExScI) with funding from NASA, the PHASES project, and the Infrared Processing and Analysis Center (IPAC).

PTI had three 40 cm apertures that could be combined pair-wise to provide baselines to 110 m. The interferometer actively tracked the white-light fringe at H and K bands, using laser-monitored active delay lines, with angle tracking implemented at R band. The instrument was highly automated, allowing for a high observing cadence. Many of the technical approaches developed at PTI have been applied at the NASA Keck Interferometer.

Most PTI science observations used a single beam on the long baseline to measure fringe visibility. However, PTI also included the capability for dual-beam narrow-angle astrometry, and was used for demonstration of this technique. In addition, PTI also carried out the PHASES single-beam very narrow-angle astrometry program.

PTI was also used to measure the sizes of dwarf, giant, and supergiant stars, the sizes of emissive regions around young stellar objects, and binary and multiple star orbits, both from visibility measurements and PHASES astrometry. It was the first interferometer to have directly measured the diameter changes of a Cepheid variable star, and to have directly measured the rotational oblateness of a rapidly rotating star.

Support for the software discussed on this page is provided on a best-effort basis.

PTI Publication List

Brief picture tour of the PTI

PTI Instrument Description:

General interferometry information:

PTI Data:

Data Access

  • Click here to download a sortable excel file containing sources and observation dates for PTI between 1997-2008.
  • Download the entire PTI archive from 1997-2008 (417 Mb)
  • Download data for an entire year or an individual date.
  • Archive description (including details of modifications made to the metadata files before inclusion in the database).

Data Product Definition

Data Calibration

Observation Planning Support
During PTI operations, NExScI provided observation planning support through the getCal planning package, a suite of tools for meshing information on stars, selecting calibrators, and computing temporal accessibility and u-v coverage.


If you have any questions on PTI data, please visit the help desk page.