Stellar kinematics of dwarf galaxies from multi-epoch spectroscopy: Application to Triangulum II

ABSTRACT We present new MMT/Hectochelle spectroscopic measurements for 257 stars observed along the line of sight to ultrafaint dwarf galaxy Triangulum II (Tri II). Combining results from previous Keck/DEIMOS spectroscopy, we obtain a sample that includes 16 likely members Tri II, with up 10 independent redshift per star. To this multi-epoch kinematic data set, apply methodology develop in order infer binary orbital parameters sparsely sampled radial velocity curves as few two epochs. For previously identified (spatially unresolved) system an solution period $296.0_{-3.3}^{+3.8} \rm ~ d$, semimajor axis $1.12^{+0.41}_{-0.24}\rm ~au$, and systemic $-380.0 \pm 1.7 ~km ~s^{-1}$ then use analysis II’s internal kinematics. Despite improvement modelling star systems, current remain insufficient resolve dispersion II. instead find 95 cent confidence upper limit $\sigma _{v} \lesssim 3.4 ~km~s^{-1}$.