We present the results of our ongoing radial-velocity survey of the old ( 7 Gyr ) open cluster NGC 188 .
Our WIYN 3.5m data set spans a time baseline of eleven years , a magnitude range of 12 \leq V \leq 16.5 ( 1.18 - 0.94 M _ { \odot } ) , and a 1° diameter region on the sky .
With the addition of a Dominion Astrophysical Observatory ( DAO ) data set we extend our bright limit to V = 10.8 and , for some stars , extend our time baseline to thirty-five years .
Our magnitude limits include solar-mass main-sequence stars , subgiants , giants , and blue stragglers , and our spatial coverage extends radially to 17 pc ( \sim 13 core radii ) .
For the WIYN data we present a detailed description of our data reduction process and a thorough analysis of our measurement precision of 0.4 km s ^ { -1 } for narrow-lined stars .
We have measured radial velocities for 1046 stars in the direction of NGC 188 , and have calculated radial-velocity membership probabilities for stars with \geq 3 measurements , finding 473 to be likely cluster members .
We detect 124 velocity-variable cluster members , all of which are likely to be dynamically hard binary stars .
Using our single member stars , we find an average cluster radial velocity of -42.36 \pm 0.04 km s ^ { -1 } .
We use our precise radial-velocity and proper-motion membership data to greatly reduce field star contamination in our cleaned color-magnitude diagram , from which we identify six stars of note that lie far from a standard single-star isochrone .
We present a detailed study of the spatial distribution of cluster member populations , and find the binaries to be centrally concentrated , providing evidence for the presence of mass segregation in NGC 188 .
We observe the blue stragglers to populate a bimodal spatial distribution that is not centrally concentrated , suggesting that we may be observing two populations of blue stragglers in NGC 188 , including a centrally concentrated distribution as well as a halo population .
Finally , we find NGC 188 to have a global radial-velocity dispersion of 0.64 \pm 0.04 km s ^ { -1 } , which may be inflated by up to 0.23 km s ^ { -1 } from unresolved binaries .
When corrected for unresolved binaries , the NGC 188 radial-velocity dispersion has a nearly isothermal radial distribution .
We use this mean corrected velocity dispersion to derive a virial mass of 2300 \pm 460 M _ { \odot } .