Surveying the Bright Stars by Optical Interferometry. I. A Search for Multiplicity Among Stars of Spectral Types F-K

Abstract

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...

Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer

“…While some of the stars presented here do have binary companions, we could disregard the secondary star in our angular diameter fits to the primary star due to the separation between the components and/or the magnitude difference between them. Hutter et al (2016) recently demonstrated that the NPOI's detection sensitivity spans 3 to 860 mas with a magnitude difference of 3.0 (for most binary systems) to 3.5 (where the component spectral types differ by less than two). Any companions to our targets were beyond those detection limits.…”

“…We used a smoothing time of 80 minutes, since that was found to be the optimal value for angular diameter measurements as described in Hutter et al (2016).…”

“…In order to characterize the stability of the wavelength scale calibration, the NPOI regularly measured the central wavelengths of all the spectrometer channels in a Fourier transform spectrometer mode starting in 2005. The measurements show the central wavelengths are stable with a 0.6 nm (0.1%) scatter (Hutter et al 2016). For data prior to 2005, we incorporated a ±0.5% error in the wavelength scale.…”

“…Table 2 lists the stars observed, the calibrators used, the dates, baselines, and number of observations. We used the "Classic" beam combiner that takes data over 16 spectral channels spanning 550 to 850 nm Hutter et al 2016). Each observation consisted of a 30-second coherent (on the fringe) scan where the fringe contrast was measured every 2 ms. Every coherent scan was paired with an incoherent (off the fringe) scan that was used to estimate the additive bias affecting fringe measurements .…”

The Disk Physical Conditions of 48 Persei Constrained by Contemporaneous Hα Spectroscopy and Interferometry

“…The NPOI has an unvignetted aperture of 35 cm with an effective aperture for the observations of 12.5 cm set by the diameter of the feed system optics. See Armstrong et al (1998) and Hutter et al (2016) for additional technical descriptions of this facility. Typically, observations from up to five unique baselines are obtained simultaneously; for this study, baseline lengths ranged from 18.9 to 64.4 m. A total of 291 squared visibility measurements from a 150Å wide spectral channel containing the Hα emission line (i.e., centered at 6563Å) of 48 Per were obtained at NPOI in the autumn of 2006.…”