  We have used high-resolution spectroscopy to observe the Kepler-16 eclipsing
binary as a double-lined system, and measure precise radial velocities for both
stellar components. These velocities yield a dynamical mass-ratio of
q=0.2994+-0.0031. When combined with the inclination, i=90.3401+0.0016-0.0019
deg, measured from the Kepler photometric data by Doyle et al. 2011, we derive
dynamical masses for the Kepler-16 components of M_A=0.654+-0.017 M_sun and
M_B=0.1959+-0.0031 M_sun, a precision of 2.5% and 1.5% respectively. Our
results confirm at the ~2% level the mass-ratio derived by Doyle et al. with
their photometric-dynamical model, q=0.2937+-0.0006. These are among the most
precise spectroscopic dynamical masses ever measured for low-mass stars, and
provide an important direct test of the results from the photometric-dynamical
modeling technique.
