WIYN open cluster study. XXXVIII. stellar radial velocities in the young open cluster M35 (NGC 2168)

We present 5201 radial-velocity (RV) measurements of 1144 stars as part of an ongoing study of the young (150Myr) open cluster M35 (NGC 2168). We have observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN 3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude range of 13.0 ≤ V ≤ 16.5 (1.6-0.8 M_⊙) and extends spatially to a radius of 30 arcmin (7pc in projection at a distance of 805pc or 4 core radii). Due to its youth, M35 provides a sample of late-type stars with a range of rotation periods. Therefore, we analyze the RV measurement precision as a function of the projected rotational velocity. For narrow-lined stars (v sin i≤ 10kms^-1), the RVs have a precision of 0.5kms^-1, which degrades to 1.0kms^-1 for stars with vsin i = 50kms ^-1. The RV distribution shows a well-defined cluster peak with a central velocity of -8.16 ± 0.05kms^-1, permitting a clean separation of the cluster and field stars. For stars with ≥3 measurements, we derive RV membership probabilities and identify RV variables, finding 360 cluster members, 55 of which show significant RV variability. Using these cluster members, we construct a color-magnitude diagram for our stellar sample cleaned of field star contamination. We also compare the spatial distribution of the single and binary cluster members, finding no evidence for mass segregation in our stellar sample. Accounting for measurement precision, we place an upper limit on the RV dispersion of the cluster of 0.81 ± 0.08kms^-1. After correction for undetected binaries, we derive a true RV dispersion of 0.65 ± 0.10kms^-1.