  The 13-16 um region observed by the Infrared Space Observatory (ISO) of
several ABG stars are discussed. We present and analyse spectra of seven M
giants which show carbon dioxide features. To explain the features of the
bands, we suggest they originate from two different circumstellar layers, one
being a warm and high density layer close to the star, possibly making the 15
um band optically thick, and the other being a large, cold and optically thin
layer extending far out in the wind. This could explain the difference in
temperatures of the different bands found in the analysis of the spectra and
the number of molecules needed for the emission. It is demonstrated that in
spite of the bands probably not being formed in vibrational LTE, the
temperatures can be estimated from the widths of the bands.
