Calculation of the Local Standard of Rest from 20,574 Local Stars in the New Hipparcos Reduction with Known Radial Velocities

Context. An accurate estimate of the local standard of rest (LSR) is required to determine key parameters used in approximate galactic mass models and to understand Galactic structure and evolution. However, authors are often forced to base dynamical analyses on potentially unreliable figures because recent determinations of the LSR have failed to reach agreement, especially with regard to the direction, V, of Galactic rotation. Aims. To explain why the traditional method for calculating the LSR fails, and to find alternative means of calculating the LSR with realistic error margins. Methods. We assemble and investigate the kinematic properties of 20 574 stars within 300pc, with complete and accurate kinematic data. The traditional method of calculating the LSR assumes a well-mixed distribution. In fact, the velocity distribution is highly structured, invalidating calculations based on mean motions and asymmetric drift. We find other indicators in the distribution which we believe give a better estimate of circular motion. Results. We find good agreement between results and give as our best estimate of the LSR (U_0, V_0, W_0) = (7.5 +- 1.0, 13.5 +- 0.3, 6.8 +- 0.1) km/s. We calculate the slope of the circular speed curve at the solar radius, finding -9.3 +- 0.9 km/s/kpc.