Millimetre observations of infrared carbon stars

II. Mass loss rates and expansion velocities

¹ Instituut voor Sterrenkunde, PACS-ICC, Celestijnenlaan 200B, 3001 Heverlee, Belgium
² Mount Stromlo and Siding Spring Observatory, Cotter road, Weston ACT, Australia
³ Kapteyn Astronomical Institute, Postbus 800, 9700 AV, Groningen, The Netherlands
⁴ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Corresponding author: M. Groenewegen, groen@ster.kuleuven.ac.be

Received: 1 March 2002
Accepted: 15 May 2002

Abstract

Dust- and gas mass loss rates and distances are determined for a sample of about 330 infra-red carbon stars that probe a distance up to about 5.5 kpc. The dependence of the dust- and gas mass loss rates, and the expansion velocity upon galactic longitude (l) are studied. It is found that the expansion velocity significantly depends on l, but that the absolute bolometric magnitude, the dust mass loss rate and the gas-to-dust ratio depend on l marginally, if at all, and the gas mass loss rate does not depend on l. Beyond the solar circle, the expansion velocity (as well as the luminosity, dust-to-gas ratio, dust mass loss rate) is lower than inside the solar circle, as expected from the overall gradient in metallicity content of the Galaxy. Combining the average expansion velocity inside and beyond the solar circle with the theoretically predicted relation between expansion velocity and gas-to-dust ratio, we find that the metallicity gradient in the solar neighbourhood is about -0.034 dex/kpc, well within the quoted range of values in the literature.