Stellar kinematics in the solar neighbourhood and the disc scale lengths of the Galaxy
O. Bienaymé and
Received 7 May 1996 / Accepted 17 January 1997
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 between 1.7 and 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 or that is constant when the vertical scale height is assumed to be constant. We explain why the measured squared axis ratio of the velocity dispersions of disc stars is less than . 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.
Key words: stars: kinematics Galaxy: kinematics and dynamics solar neighbourhood Galaxy: structure
Send offprint requests to: O. Bienaymé
© European Southern Observatory (ESO) 1997
Online publication: May 26, 1998