The evolution of carbon stars in the Magellanic Clouds.

JHK photometric data are presented for over 100 field carbon stars in the Small Magellanic Cloud and for 10 in the Large Cloud together with spectroscopic results for about half of them. These data are combined with previously published data for a discussion of the luminosity-temperature distribution of the field carbon stars in the Magellanic Clouds. In the Small Cloud we have found carbon stars at higher temperatures and lower luminosities than previously observed. The faintest are below the top of the red giant branch. Their formation can thus hardly be explained by thermal pulses along the asymptotic giant branch so that other evolutionary processes may have to he considered. The medium- and low-luminosity C stars in the M-C transition zone have a low C_2_ content. At these luminosities most of the J-type stars are found close to the C_2_ -poor stars in the HR diagram. Their C_2 _ content is, however, about as high as in the coolest, most evolved C stars. It appears likely that we see two scenarios of the formation of carbon stars: one being M-S-C(C_2_- poor)-C, the other M-J-C. In the Large Cloud a number of high-luminosity J-type stars appear in the HR diagram between the M giant stars and the high-luminosity MS-type stars. They may represent a brief ^13^C producing stage in the evolution of the more massive AGB stars.