C stars as kinematic probes of the Milky Way disk from 9 to 15 kpc

Abstract

Context. The availability, from 2MASS, of a large homogeneous sample of Galactic C stars and the recognition that their absolute magnitude can be accurately determined offer the possibility to use them as kinematical probes to investigate motions in the thin or thick disks. Aims. Determine the radial velocities for 70 C stars, a few degrees from the Galactic plane and distributed in longitudes from 60° to 220°. Methods. Spectra, with a resolution of 4300, were obtained with the DAO 1.8 m telescope during 6 beautiful nights in October 2006. Results. The rotation velocities of C stars with 60° < ℓ < 150° suggest a flat rotation curve to 15 kpc. A number of stars have velocities that do not fit the thin disk rotation. Some of them, toward l = 200° are most probably members of the Canis Major overdensity. Conclusions. Effort should be made to extend the rotation curve to more that 20 kpc. © ESO 2007.