M supergiants and the low metal abundances in the Small Magellanic Cloud

BVRI photometry of 25 spectroscopically confirmed M supergiants in the Small Magellanic Cloud (SMC) is discussed. It is found that one of these stars is of spectral type M1 and that the rest have spectral types M0 or earlier. Two-color plots are presented which show that only one M supergiant in the SMC may be as late as M2. It is suggested that lower metallicities in the SMC may produce lower opacities in the atmospheres of cool supergiants, so that the spectra originate in somewhat warmer layers and give rise to earlier spectral types.