Proceedings Article | 9 June 1994
KEYWORDS: Aluminum, Interferometers, Stars, Visibility, Signal to noise ratio, Optical arrays, Buildings, Modulation, Control systems, Retroreflectors
The Navy Prototype Optical Interferometer (NPOI) is nearing the completion of the first phase of construction at the Lowell Observatory on Anderson Mesa, AZ. The NPOI comprises two sub- arrays, the Big Optical Array (BOA) and the USNO Astrometric Interferometer (AI), which share delay lines, the optics laboratory, the control system, and parts of the feed optics. We describe the design of and progress on the BOA, the imaging component of the NPOI. The AI is described elsewhere (Hutter, these proceedings). As of the date of this symposium, most of the civil engineering is complete, including the control and laboratory buildings and the concrete piers for the initial array. Three AI siderostats and associated feed pipes, three delay lines, the initial three-way beam combiner, and much of the control system are in place. First fringes are anticipated in April. By the end of 1994, four AI and two BOA siderostats, as well as three more delay lines, will be installed, making imaging with all six siderostats possible. The complete BOA will consist of six 50 cm siderostats and 30 siderostat stations in a Y with 251 m arms, with baseline lengths from 4 m to 437 m. Nearly redundant baseline lengths will allow fringe tracking on long baselines on which the visibilities are too low for detection in real time. A six-way beam combiner (Mozurkewich, these proceedings) will allow simultaneous measurements of 15 visibilities and nine of 10 independent closure phases. The output beams will feed 32-channel spectrometers covering the range from 450 to 900 nm. We anticipate tracking fringes on stars brighter than 10m, imaging surfaces of stars brighter than 4m, measuring stellar diameters to 0.18 milliarcsec (mas), and measuring binary orbits with major axes as small as 0.4 mas.
