W. J. Maciel -
Abstract #63
THE ROTATION CURVE OF THE GALAXY OBTAINED FROM PLANETARY NEBULAE AND AGB STARS
L. H. Amaral, R. Ortiz, J. R. D. Lépine, W. J. Maciel
Monthly Notices Roy. Astron. Soc. 281, 339-347 (1996) The rotation curve of the Galaxy is obtained from a sample of planetary nebulae and asymptotic giant branch (AGB) stars. The AGB stars are OH/IR stars and carbon-rich stars with large mass-loss rates, with velocities known from radio observations and distances determined from their infrared luminosity. The rotation curve exhibits a steep decrease in the solar vicinity, and a minimum at about 8.5 kpc (adopting Ro = 7.9 kpc). We fit the rotation curve with a mass distribution model of the Galaxy, based on the model for star counts in the infrared region of Ortiz and Lépine; the main components are a spherically symmetric density distribution that represents the bulge and the halo, and two exponential disc components with scalelengths 2.6 and 4.5 kpc. A good agreement is found between the star count model and the rotation curve. A minimum is observed at 8.5 kpc; possible explanations are discussed. The surface density of the disc in the solar neighbourhood is 77 Mo/pc2, not very different form the value predicted by star counts. This result implies that there is no need for a dark matter component, at least up to a radius of about 12 kpc.
