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Session 54 - Ground and Instrumentation Techniques and Catalogs.
Display session, Wednesday, June 12
Tripp Commons,

[54.10] The Navy Prototype Optical Interferometer

J. A. Benson, D. J. Hutter, N. M. Elias II, P. Bowers (US Naval Obs.), D. Mozurkewich, J. T. Armstrong (NRL), N. White (Lowell Obs.), C. Hummel (USRA)

This paper announces the first closure phase measurements made with the Navy Prototype Optical Interferometer (NPOI) on stars. These are the first closure phase measurements made at optical wavelengths which exceed, by a factor of two to three, the resolution of the largest existing single optical telescope. The first observations were made on 1996 March 18 using three of the NPOI's four astrometric stations with baselines of 18.9, 22.2, and 37.5 meters. These data, the NPOI, and its current status will be discussed.

The NPOI is a long baseline optical interferometer built by NRL, USNO, and Lowell Observatory on Anderson Mesa, near Flagstaff, AZ, USA. It is designed for astrometry and for imaging stellar surfaces. First fringe measurements with a single baseline were made in October 1994. The intervening time was spent adding a third telescope and making numerous upgrades to the equipment and software.

The astrometric portion of the array consists of four stations in a Y-shaped configuration. The baselines between these stations are monitored by an extensive laser metrology system. The goal of this system is to catalog stellar positions with milliarcsecond accuracy. Baseline lengths range from 18.9 to 37.5 meters.

The imaging portion of the array will contain 6 elements that can be deployed on any of 30 stations. These stations are also arranged in a Y configuration with a maximum baseline length of 435 meters.

The wavelength coverage for both systems is 450 to 850 nm, divided into 32 spectral channels. The system incorporates active group delay fringe tracking and rapid tip-tilt angle tracking. There are plans for adding two micron capability. The maximum aperture is currently 12.5 cm. Beam compressors are planned to increase the apertures to 35 cm. So far, the faintest star on which we have tracked fringes is m_V = 4.0.

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