The Keck Interferometer

Abstract

The Keck Interferometer (KI) combined the two 10 m W. M. Keck Telescopes on Mauna Kea as a long-baseline near- and mid-infrared interferometer. Funded by NASA, it operated from 2001 until 2012, and addressed a broad range of science topics. KI included the capability for high sensitivity fringe-visibility measurement at H, K, and L bands, and for nulling measurements at 10 um. KI used adaptive optics on the two Kecks to correct the pupil, as well as active fringe tracking in all modes for pathlength control, including implementation of cophasing for increased sensitivity. Supporting these capabilities was an extensive interferometer infrastructure and unique instrumentation, including some additional capabilities added as part of the NSF-funded ASTRA program. This paper provides an overview of the instrument architecture and some of the key early design and implementation decisions, as well as a description of all of the key elements as they were implemented at the end of the project, with an objective of providing a view of KI as an integrated system, and to provide adequate technical detail to assess the implementation.. Included is a discussion of the operational aspects of the system, as well as the achieved system performance. Finally, we include details on V2 calibration in the presence of detector nonlinearities as applied in our data pipeline.