Palomar Testbed Interferometer

{{Short description|Astronomical instrument in California}}

{{Infobox telescope|location=Palomar Mountain, California, US}}

The Palomar Testbed Interferometer (PTI) was a near infrared, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County, California, United States. It was built by Caltech and the Jet Propulsion Laboratory and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer. It began operations in 1995 and achieved routine operations in 1998, producing more than 50 refereed papers in a variety of scientific journals covering topics from high precision astrometry{{cite journal |author=M. Shao |title=Differential Astrometry of the 61 Cygni System with the Palomar Testbed Interferometer |journal=Bulletin of the American Astronomical Society |date=1999 |volume=31 | pages=1504 | bibcode=1999AAS...195.8714S |name-list-style=vanc |display-authors=1 |last2=Boden |first2=A. F. |last3=Colavita |first3=M. M. |last4=Lane |first4=B. F. |last5=Lawson |first5=P. R. |collaboration=PTI Collaboration}} to stellar masses,{{cite journal |last1=Boden|first1=Andrew F. |last2=Torres|first2=Guillermo |last3=Hummel|first3=Christian A. |title=Testing Stellar Models with an Improved Physical Orbit for 12 Bootis |journal=The Astrophysical Journal |date=1 July 2005 |volume=627 |issue=1 |pages=464–476 |doi=10.1086/430058 |arxiv = astro-ph/0502250 |bibcode=2005ApJ...627..464B|s2cid=834038 }} stellar diameters and shapes.{{cite journal |last=van Belle |first=G. T. |author2=Creech-Eakman, M. J. |author3=Hart, A. |title=Supergiant temperatures and linear radii from near-infrared interferometry |journal=Monthly Notices of the Royal Astronomical Society |date=21 April 2009 |volume=394 |issue=4 |pages=1925–1935 |doi=10.1111/j.1365-2966.2008.14146.x |doi-access=free |bibcode = 2009MNRAS.394.1925V |arxiv = 0811.4239 |s2cid=118372600 }} PTI concluded operations in 2008 and has since been dismantled.{{cite web|title=Caltech Astronomy - The Palomar Testbed Interferometer (PTI) |url=http://www.astro.caltech.edu/palomar/about/telescopes/decommissioned.html#pti |publisher=Caltech Astronomy |accessdate=2014-12-09}}

PTI was notable for being equipped with a "dual-star" system, making it possible to simultaneously

observe pairs of stars; this cancels some of the atmospheric effects of astronomical seeing and makes very high precision measurements possible.{{Citation needed|date=January 2012}}

A groundbreaking study with the Palomar Testbed Interferometer revealed that the star Altair is not spherical, but is rather flattened at the poles due to its high rate of rotation.{{cite journal |last=van Belle |first=Gerard T. |author2=Ciardi, David R. |author3=Thompson, Robert R. |author4=Akeson, Rachel L. |author5=Lada, Elizabeth A. |title=Altair's Oblateness and Rotation Velocity from Long-Baseline Interferometry |journal=The Astrophysical Journal |date=1 October 2001 |volume=559 |issue=2 |pages=1155–1164 |doi=10.1086/322340 |bibcode = 2001ApJ...559.1155V |s2cid=13969695 }}