Infrared spectra of AGB stars in external galaxies, and their implications on abundances

M. Matsuura¹, A.A. Zijlstra¹, J.Th. van Loon ² et al.

¹UMIST, UK
²Keele Univ., UK

We have obtained L-band spectra of AGB stars in the Large and Small Magellanic Clouds, and the Sagittarius Dwarf Galaxy. In L-band, C2H2 and HCN bands are found in carbon-rich AGB stars, and SiO and H2O bands in oxygen-rich stars. C2H2 and HCN are more abundant in carbon-rich stars in these galaxies than those in our Galaxy, suggesting a high carbon abundance in the atmosphere of extra-galactic AGB stars. The amount of enriched carbon during the third dredge-up, could depend on the metallicity of these galaxies. On the other hand, SiO lines are not detected in LMC oxygen-rich stars, probably due to the lower elemental abundance of Si. The analysis of these molecular bands shows the effect of metallicity on the atmosphere of AGB stars, and the effect of abundance change via the third dredge-up. LMC spectra of this work is published in Matsuura et al. (2000, ApJ, 580, L133).