We present the first results from an ongoing survey for multiplicity among the bright stars using the Navy Precision Optical Interferometer (NPOI). We first present a summary of NPOI observations of known multiple systems, including the first detection of the companion of β Scuti with precise relative astrometry, to illustrate the instrument's detection sensitivity for binaries at magnitude differences ∆m 3 over the range of angular separation 3 -860 milliarcseconds (mas). A limiting ∆m 700 ∼ 3.5 is likely for binaries where the component spectral types differ by less than two. Model fits to these data show good agreement with published orbits, and we additionally present a new orbit solution for one of these stars, σ Her. We then discuss early results of the survey of bright stars at δ ≥ -20 • . This survey, which complements previous surveys of the bright stars by speckle interferometry, initially emphasizes bright stars of spectral types F0 through K2. We report observations of 41 stars of apparent visual magnitude m V ≤ 4.30, all having been observed on multiple nights. Analysis of these data produces fitted angular separations, position angles, and component magnitude differences for six previously known visual binaries. Three additional systems were examined as possible binaries, but no conclusive detection could be made.No evidence of close stellar companions within our detection limit of ∆m ≈ 3 was found for the remaining 32 stars observed; however, uniform-disk angular diameters are reported for 11 of the resolved stars in this last group.modeling of previously known binary systems ( § 4.2, 5.1), plus detected binaries among the program stars ( § 5.2, 5.3), to determine the maximum detected magnitude difference (∆m) of binary star pairs in our survey as a function of their angular separation ( § 5.5);and, third, the subsidiary result of accurate angular diameters for the resolved, single stars among the program sample ( § 5.6). Plans for future stages of this survey are also discussed ( § 6). The NPOIThe NPOI (Armstrong et al. 1998) located on Anderson Mesa, AZ, is a joint project of the U. S. Naval Observatory and the Naval Research Laboratory in cooperation with Lowell Observatory. A brief description of the instrument and the specific configuration used in the observations reported in this paper are as follows. 2.1. Instrumentation 2.1.1. Siderostat Arrays The NPOI includes arrays for both imaging and astrometry. The four stations of the astrometric array (AC, AE, AN, and AW) are fixed and feature a laser metrology system for monitoring the siderostat pivot (Hutter & Elias 2002). Six additional imaging siderostats are operational at the E03, E06, E07, N03, W04, and W07 stations. The resulting baselines range from 9.8 m (AC-W04) to 97.6 m (E07-W07). Recently constructed shelters at the E10, N06, N07, and W10 piers will allow the commissioning of additional baselines of up to 432 m (E10-W10) in the near future through reconfiguration of the six imaging siderostats. The unvignetted aperture is the same f...

Visible-light long baseline interferometry holds the promise of advancing a number of important applications in fundamental astronomy, including the direct measurement of the angular diameters and oblateness of stars, and the direct measurement of the orbits of binary and multiple star systems. To advance, the field of visible-light interferometry requires development of instruments capable of combining light from 15 baselines (6 telescopes) simultaneously. The Visible Imaging System for Interferometric Observations at NPOI (VISION) is a new visible light beam combiner for the Navy Precision Optical Interferometer (NPOI) that uses single-mode fibers to coherently combine light from up to six telescopes simultaneously with an image-plane combination scheme. It features a photometric camera for calibrations and spatial filtering from single-mode fibers with two Andor Ixon electron multiplying CCDs. This paper presents the VISION system, results of laboratory tests, and results of commissioning on-sky observations. A new set of corrections have been determined for the power spectrum and bispectrum by taking into account non-Gaussian statistics and read noise present in electron-multipying CCDs to enable measurement of visibilities and closure phases in the VISION post-processing pipeline. The post-processing pipeline has been verified via new on-sky observations of the O-type supergiant binary ζ Orionis A, obtaining a flux ratio of 2.18 ± 0.13 with a position angle of 223.9 ± 1.0 • and separation 40.6 ± 1.8 mas over 570-750 nm, in good agreement with expectations from the previously published orbit.2. Mount the 70 /20 beam splitters and accompanying beam-shear compensating windows. The beam splitters route light from the feed system to the VISION optical bench.

We measured the angular diameters of 44 stars with the Navy Precision Optical Interferometer, obtaining uncertainties on the limb-darkened diameter of 2% or less for all but four stars. We then used our diameters with Gaia or Hipparcos parallaxes to calculate each star’s physical radius. We gathered information from the literature to determine bolometric flux and luminosity, and combined that with our diameters to produce an effective temperature. Our sample consists of mostly giant stars, and spans a wide range of spectral classes from B to M.

We present the results of a multiplicity survey for a magnitude-limited sample of 31 classical Be stars conducted with the Navy Precision Optical Interferometer and the Mark III Stellar Interferometer. The interferometric observations were used to detect companions in ten previously known binary systems. For two of these sources (66 Oph and β Cep) new orbital solutions were obtained, while for a third source (υ Sgr) our observations provide the first direct, visual detection of the hot sdO companion to the Be primary star. Combining our interferometric observations with an extensive literature search, we conclude that an additional four sources (o Cas, 15 Mon, β Lyr, and β Cep) also contain wider binary components that are physical companions to the narrow binaries, thus forming hierarchical multiple systems. Among the sources not previously confirmed as spectroscopic or visual binaries, BK Cam was resolved on a number of nights within a close physical proximity of another star with relative motion possibly suggesting a physical binary. Combining our interferometric observations with an extensive literature search, we provide a detailed listing of companions known around each star in the sample, and discuss the multiplicity frequency in the sample. We also discuss the prospects for future multiplicity studies of classical Be stars by long baseline optical interferometry.

We measured the angular diameters of six stars using the six-element observing mode of the Navy Precision Optical Interferometer (NPOI) for the first time since the early 2000s. Four of the diameters ranged from 1.2 to 1.9 mas, while the two others were much smaller at approximately 0.5 mas to 0.7 mas, which are the two smallest angular diameters measured to date with the NPOI. There is a larger spread in the measurements than data obtained with three-, four-, or five-element modes, which can be attributed in part to the flux imbalance due to the combination of more than two siderostats in a single spectrograph, and also to crosstalk between multiple baselines related to nonlinearities in the fast-delay-line dither strokes. We plan to address this in the future by using the VISION beam combiner.