Vertical distribution of Galactic disk stars^*

II. The surface mass density in the Galactic plane

¹ Observatoire Astronomique de Strasbourg, UMR 7550, Université Louis Pasteur, 67000 Strasbourg, France
² Observatoire Aquitain des Sciences de l'Univers, UMR 5804, 2 rue de l'Observatoire, 33270 Floirac, France

Corresponding author: A. Siebert, siebert@astro.u-strasbg.fr

Received: 25 July 2002
Accepted: 12 November 2002

Abstract

High resolution spectral data of red clump stars towards the NGP have been obtained with the high resolution spectrograph Elodie at OHP for Tycho-2 selected stars. Combined with Hipparcos local analogues, we determine both the gravitational force law perpendicular to the Galactic plane and the total surface mass density and thickness of the Galactic disk. The surface mass density of the Galactic disk within 800 pc derived from this analysis is Σ (800   = 76  and, removing the dark halo contribution, the total disk mass density is  = 67  at solar radius. The thickness of the total disk mass distribution is dynamically measured for the first time and is found to be 390 pc in relative agreement with the old stellar disk scaleheight. All the dynamical evidences concerning the structure of the disk (its local volume density – i.e. the Oort limit–, its surface density and its thickness) are compatible with our current knowledge of the corresponding stellar disk properties.