Spectroscopy of Tri II LOS and member stars

Combining results from previous Keck/DEIMOS spectroscopy, we obtain a sample that includes 16 likely members of Tri II, with up to 10 independent redshift measurements per star. To this multi-epoch kinematic data set, we apply methodology that we develop in order to infer binary orbital parameters from sparsely sampled radial velocity curves with as few as two epochs.

For a previously identified (spatially unresolved) binary system in Tri II, we infer an orbital solution with period 296.0^+3.8^_-3.3_ d, semimajor axis 1.12^+0.41^_-0.24_ au, and systemic velocity -380.0 +/- 1.7 km/s that we then use in the analysis of Tri II's internal kinematics. Despite this improvement in the modelling of binary star systems, the current data remain insufficient to resolve the velocity dispersion of Tri II.