STELLAR KINEMATICS IN THE SOLAR NEIGHBORHOOD AND THE DISC SCALE LENGTHS OF THE GALAXY

A general dynamically consistent 2D flat distribution function is buil t to model the kinematics of neighbouring stars. Application leads to the measurement of a short galactic scale length R-rho between 1.7 and 2.9 kpc 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(rho) = R-sigma or that sigma(z)(R)/sigma(R)(R) is constant when the vertical scale height h(z) (R) is assumed to be constant. We explain why the me asured squared axis ratio of the velocity dispersions sigma(v)(2)/sigm a(u)(2) 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. W e show that this is not the case and that it may be simply explained w ith a realistic axisymmetric disc model if the circular velocity is lo cally declining or if there is a mismatch between the photometric and kinematic scale lengths.