Luminous carbon stars in the Magellanic Clouds

We present ground-based 3 mu m spectra of obscured Asymptotic Giant Branch (AGB) stars in the Magellanic Clouds (MCs). We identify the carbon stars on the basis of the 3.1 mu m absorption by HCN and C2H2 molecules. We show evidence for the existence of carbon stars up to the highest AGE lu minosities (M-bol = -7 mag, for a distance modulus to the LMC of 18.7 mag). This proves that Hot Bottom Burning (HBB) cannot, in itself, prevent massi ve AGE stars from becoming carbon star before leaving the AGE. It also sets an upper limit to the distance modulus of the Large Magellanic Cloud of 18 .8 mag. The equivalent width of the absorption band decreases with redder (K - L) c olour when the dust continuum emission becomes stronger than the photospher ic emission. Carbon stars with similar (K - L) appear to have equally stron g 3 mu m absorption in the MCs and the Milky Way. We discuss the implicatio ns for the carbon and nitrogen enrichment of the stellar photosphere of car bon stars.