Galactic mass-losing AGB stars probed with the IRTS. I.

¹ DEMIRM, UMR 8540, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
² Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
³ Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
⁴ UMIST, Department of Physics, PO Box 88, Manchester M60 1QD, UK
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Infrared Astrophysics Branch, Code 685, Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁷ Department of Physics, Catholic University of America, Washington, DC 20064, USA

Corresponding author: T. Le Bertre, Thibaut.LeBertre@obspm.fr

Received: 25 April 2001
Accepted: 12 July 2001

Abstract

AGB mass-losing sources are easy to identify and to characterize in the near-infrared range (1-5 μm). We make use of the near-infrared data acquired by the Japanese space experiment IRTS to study a sample of sources detected in the 2 celestial strips surveyed by the IRTS. Mass-loss rates and distances are estimated for 40 carbon-rich sources and 86 oxygen-rich sources of which 8 are probably of S-type. Although the sample is small, one sees a dependence of the relative contribution of the two kinds of sources to the replenishment of the interstellar medium (ISM) on the galactocentric distance. E.g. from 6 to 8 kpc, oxygen-rich sources in our sample contribute 10-12 times as much as carbon rich sources, whereas from 10 to 12 kpc, the latters contribute 3-4 times as much as the formers. Therefore, one would expect a gradient in the composition of the ISM between 6 and 12 kpc from the Galactic Centre, especially in its dust component. Most of the replenishment (>50% ) by AGB stars is due to sources with mass-loss rate larger than 10 yr^-1.