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

Abstract

We are using the 2002 data-release from the Japanese space experiment IRTS to investigate the spatial distribution of galactic mass-losing (>2×10-8 M⊙ yr-1) AGB stars and the relative contribution of C-rich and O-rich ones to the replenishment of the ISM. Our sample contains 126 C-rich and 563 O-rich sources which are sorted on the basis of the molecular bands observed in the range 1.4-4.0 μm, and for which we estimate distances and mass loss rates from near-infrared photometry (K and L′). There is a clear dependence on galactocentric distance, with O-rich sources outnumbering C-rich ones for rGC < 8 kpc. and the reverse for rGC > 10 kpc. The contribution to the replenishment of the ISM by O-rich AGB stars relative to C-rich ones follows the same trend. Although they are rare (∼10% in our sample), sources with 10-6 M⊙ yr-1 < M < 10-5 M⊙ yr-1 dominate the replenishment of the ISM by contributing to ∼50% of the total of the complete sample. We find 2 carbon stars at more than 1 kpc from the Galactic Plane, that probably belong to the halo of our Galaxy.