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Session 16 - Astrometry.
Display session, Wednesday, January 07
Exhibit Hall,

[16.02] First Astrometric Results from the NPOI

D. J. Hutter, N. M. Elias II, C. A. Hummel (U.S. Naval Observatory)

The Navy Prototype Optical Interferometer (NPOI), a joint project of the U.S. Naval Observatory, the Naval Research Laboratory, and Lowell Observatory has been in routine operation since 1996. Here, we present the first results of wide-angle astrometric observations made with the NPOI.

The NPOI includes arrays for imaging and for astrometry. The imaging array consists of six movable siderostats, with baseline lengths from 2.0 m to 437 m. The astrometric array consists of four fixed siderostats, with baseline lengths from 18 m to 38 m. The astrometric array includes an extensive baseline metrology system to measure the motions of the siderostats with respect to the local bedrock to 100 nm accuracy. The arrays share vacuum feed and delay systems, active group-delay fringe tracking in 32 channels over a bandpass from 450 to 850 nm, and a high degree of automation.

The goal of the astrometry program with the NPOI is an accuracy of 2 mas over large angles. This accuracy is comparable to that achieved by the Hipparcos satellite, and will be used to maintain the optical reference frame. (Positional accuracies in that frame would otherwise degrade to 10 mas by 2001.) In addition to maintaining accurate positions for several thousand Hipparcos stars, the NPOI will also greatly improve the proper motion accuracy by increasing the measurement time base. Astrometric observations of radio stars with the NPOI will maintain the link between the optical and radio reference frames, while imaging observations will improve the link by elucidating the relation between the radio and optical emission in these systems.

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