First observations with a co-phased six-station optical long-baseline array:: Application to the triple star η Virginis

We report on the first successful simultaneous combination of six independent optical telescopes in an interferometric array. This is double the number of independent telescopes, and 5 times the number of independent baselines, heretofore combined simultaneously. This was accomplished with the Navy Prototype Optical Interferometer at Lowell Observatory, near Flagsta., Arizona. We describe the main technologies demonstrated, including hybrid six-way beam combination, nonredundant multiple optical path modulation for fringe separation, and the fringe detection electronics. To test the array's suitability for high-resolution stellar imaging, we observed the hierarchical triple star eta Virginis, and we present the first images resolving all three components. The orbital motions of these stars were followed during winter and spring of 2002. Preliminary, astrometrically determined orbits of the two components in the close pair by reference to the tertiary were derived. This enabled the estimation of the mass ratio (1.27) of the components in the close pair. We also determined the relative orbital inclination to be 31degrees. Future work needed to improve the calibration of the data is discussed.