Surveying the bright stars by optical interferometry. I. A search for multiplicity among stars of spectral types F-K

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 Δm < 3 over the range of angular separation 3-860 milliarcseconds (mas). A limiting Δm₇₀₀ ∼ 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 using 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 Δm ≈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.