The Solar Neighborhood. XLVI. Revealing New M Dwarf Binaries and Their Orbital Architectures

We use 20 yr of astrometric data from the REsearch Consortium On Nearby Stars (RECONS) program on the Cerro Tololo Inter-American Observatory/SMARTS 0.9 m telescope to provide new insight into multiple star systems in the solar neighborhood. We provide new and updated parallaxes for 210 systems and derive nine high-quality astrometric orbits with periods of 2.49-16.63 yr. Using a total of 542 systems' parallaxes from RECONS, we compare systems within 25 pc to Gaia DR2 to define criteria for selecting unresolved astrometric multiples from the DR2 results. We find that three out of four unresolved multistar red dwarf systems within 25 pc in DR2 have parallax_error >= 0.32 mas, astrometric_gof_al >= 56, astrometric_excess_noise_sig >= 108.0, ruwe >= 2.0, and parallaxes more than similar to 10% different from the long-term RECONS results. These criteria have broad applications to any work targeting nearby stars, from studies seeking binary systems to efforts targeting single stars for planet searches.