Galactic rotation and solar motion from stellar kinematics

I present three methods to determine the distance to the Galactic Centre R-0, the solar azimuthal velocity in the Galactic rest frame V-g,(circle dot) and hence the local circular speed V-c at R-0. These simple, model-independent strategies reduce the set of assumptions to near-axisymmetry of the disc and are designed for kinematically hot stars, which are less affected by spiral arms and other effects. The first two methods use the position-dependent rotational streaming in the heliocentric radial velocities (U). The resulting rotation estimate theta from U velocities does not depend on V-g,(circle dot). The first approach compares this with rotation from the Galactic azimuthal velocities to constrain V-g,(circle dot) at an assumed R-0. Both V-g,(circle dot) and R-0 can be determined using the proper motion of Sgr A* as a second constraint. The second strategy makes use of theta being roughly proportional to R-0. Therefore a wrong R-0 can be detected by an unphysical trend of V-g,(circle dot) with the intrinsic rotation of different populations. From these two strategies I estimate R-0 = (8.27 +/- 0.29) kpc and V-g,(circle dot) = (250 +/- 9) km s(-1) for a stellar sample from Sloan Extension for Galactic Understanding and Exploration, or, respectively, V-c = (238 +/- 9) km s(-1). The result is consistent with the third estimator, where I use the angle of the mean motion of stars, which should follow the geometry of the Galactic disc. This method also gives the solar radial motion with high accuracy. The rotation effect on U velocities must not be neglected when measuring the solar radial velocity U-circle dot. It biases U-circle dot in any extended sample that is lop-sided in position angle alpha by of the order of 10 km s(-1). Combining different methods I find U-circle dot similar to 14 km s(-1), moderately higher than previous results from the GenevaCopenhagen Survey.