High‐Precision Stellar Radial Velocities in the Galactic Center

We present radial velocities for 85 cool stars projected onto the centralparsec of the Galaxy. The majority of these velocities have relative errors of$\sim$1 km/s, or a factor of $\sim$30-100 smaller than those previouslyobtained with proper motion or other radial velocity measurements for a similarstellar sample. The error in a typical individual stellar velocity, includingall sources of uncertainty, is 1.7 km/s. Two similar data sets were obtainedone month apart, and the total error in the relative velocities is 0.80 km/s\in the case where an object is common to both data sets. The data are used tocharacterize the velocity distribution of the old population in the GalcticCenter. We find that the stars have a Gaussian velocity distribution with amean heliocentric velocity of $-10.1\pm$11.0 km/s (blueshifted) and a standarddeviation of 100.9$\pm7.7$ km/s; the mean velocity of the sample is consistentwith no bulk line-of-sight motion with respect to the Local Standard of Rest.At the 1 sigma level, the data are consistent with a symmetric velocitydistribution about any arbitrary axis in the plane of the sky. We find evidencefor a flattening in the distribution of late-type stars within a radius of$\sim$0.4 \pc, and infer a volume density distribution of r$^{-1/4}$ in thisregion. Finally, we establish a first epoch of radial velocity measurementswhich can be compared to subsequent epochs to measure small accelerations (1km/s/yr), corresponding to the magnitude expected over a timespan of severalyears for stars nearest to Sgr A*.