Carbon and M-type giant stars in the Magellanic Clouds

Abstract

THE late M- and C-type giant stars are of special interest in studies of stellar and galactic evolution as they are found at the extreme low temperature limit which stars first reach after evolving away from the main sequence, and also because they show remarkably different galactic distribution. Because of the pronounced strength of absorption bands of molecular oxides and of the carbon and cyanogen molecules in the spectra of these stars, extremely small dispersions can be used. Modern large telescopes equipped with Ritchey–Cretien optics allow relatively large fields to be surveyed to faint limiting magnitudes. Thus stars can be segregated and classified whose distance moduli are 22 mag and more. Now stellar populations can be sampled and surveys made of the distribution of the stars in space in the Magellanic Clouds and in the less obscured regions near the galactic centre. Three such surveys are described here. They indicate that unsuspected differences in the mixture of C and late M giant stars exist in the nuclear bulge of the galaxy and in various regions of the Magellanic Clouds. Such studies also yield new information concerning the intrinsic luminosities of C and M giant stars in these three galactic systems.