Cool dwarfs in wide multiple systems: Paper 2: A distant M8.5V companion to HD 212168 AB

Abstract

DENIS J222644.3-750342 is a nearby, very-low-mass, M8.5 V-type star that has been repeatedly targeted by kinematic and activity studies. Thought to be an isolated star, it is actually a wide common-proper-companion at 265 arcsec from the bright G0 V Hipparcos star HD 212168. The third member in the trio is CD-75 1242, a poorly investigated K dwarf. We confirm the physical binding of the triple system, to which we call Koenigstuhl 5, by compiling common radial velocities and proper-motions and measuring constant angular separations and position angles between components A, B and C over very long time baselines (A-B: 114 yr; A-C: 22 yr). With about 0.095 Msol, the M8.5 V star at 6090 AU to the G0 V primary is one of the least-bound, ultracool dwarfs in multiple systems.