Determination of Galactic Rotation Parameters and the Solar Galactocentric Distance Ro from 73 Masers

We have determined the Galactic rotation parameters and the solar Galactocentric distance R_0 by simultaneously solving Bottlinger's kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric distances from 3 to 14 kpc. The solutions found are Omega_0 = 28.86 +/- 0.45 km/s/kpc, Omega'_0 = -3.96 +/- 0.09 km/s/kpc^2, Omega"_0 =0.790 +/- 0.027 km/s/kpc^3, and R_0=8.3 +/- 0.2 kpc.In this case, the linear rotation velocity at the solar distance Ro is V_0=241 +/- 7 km/s. Note that we have obtained the Ro estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.

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