Companions to nearby stars with astrometric acceleration. II

Abstract

Hipparcos astrometric binaries were observed with the NICI adaptive optics system at Gemini-S, completing the work of Paper I (Tokovinin et al. 2012). Among the 65 F, G, K dwarfs within 67pc of the Sun studied here, we resolve 18 new sub-arcsecond companions, re-measure 7 known astrometric pairs, and establish the physical nature of yet another three wider companions. The 107 astrometric binaries targeted at Gemini so far have 38 resolved companions with separations under 3". Modeling shows that bright enough companions with separations on the order of an arcsecond can perturb the Hipparcos astrometry when they are not accounted for in the data reduction. However, the resulting bias of parallax and proper motion is generally below formal errors and such companions cannot produce fake acceleration. This work contributes to the multiplicity statistics of nearby dwarfs by bridging the gap between spectroscopic and visual binaries and by providing estimates of periods and mass ratios for many astrometric binaries.

Accepted by the Astronomical Journal. 8 pages, 4 figures

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• Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars
• New orbits based on speckle interferometry at SOAR. II
• Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars
• A New Method for Target Selection in Direct Imaging Programs with COPAINS
• A new white dwarf companion to the $\Delta \mu$ star GJ 3346