1997A&A...323..781B

A general dynamically consistent 2D flat distribution function is built to model the kinematics of neighbouring stars. Application leads to the measurement of a short galactic scale length R_ρ between 1.7 and 2.9kpc and a locally decreasing rotation curve. This is in agreement with recent determinations based on kinematics and counts of distant stars. These results rule out the classical assumption that 2R_ρ=R_σ or that σ_z(R)/σ_R(R) is constant when the vertical scale height h_z(R) is assumed to be constant. We explain why the measured squared axis ratio of the velocity dispersions σ_v²/σ_u² of disc stars is less than 1/2. This ratio has been claimed to be important evidence for the non-axisymmetry of the galactic disc. We show that this is not the case and that it may be simply explained with a realistic axisymmetric disc model if the circular velocity is locally declining or if there is a mismatch between the photometric and kinematic scale lengths.