The solar neighborhood. VII. Discovery and characterization of nearby multiples in the Ctio parallax investigation

Abstract

We report the discovery of eight new multiple star systems among 191 stellar systems targeted for parallax determinations in the RECONS (Research Consortium on Nearby Stars) southern parallax program, CTIOPI (Cerro Tololo Inter-American Observatory Parallax Investigation). The eight new companions have separations of 1>42 to 14>90 and instrumental magnitude differences at VRI of 0.06–6.07 mag. Orbital motion has not been detected in any of these systems. These new companions increase the multiplicity fraction of this sample, made up primarily of nearby (less than 25 pc) M dwarfs, to 15%. Comparison with samples that have been more completely scrutinized for companions indicates that probably only half of all multiples have so far been discovered. Given the large number of frames acquired for the astrometric series, the eight new systems and 16 known multiples have been searched for variability at VRI during the 3 year duration of CTIOPI. A flare has been detected in the secondary of the RX J1132 264 system, while at least one component in the GJ 2006 system is a probable long-term variable. Variables were detected in only 9% of the systems searched, primarily as a result of the restrictive 0.05 mag threshold required for variability confirmation