MOLECULES OF NON-PHOTOSPHERIC ORIGIN IN RED GIANTS AND SUPERGIANTS REVEALED BY THE ISO SWS

Overall SEDs based on ISO SWS observations show fair agreement with ph otospheric model predictions for red (super)giant stars. However, some details of molecular spectra cannot be explained by a photospheric or igin. In particular, fine structure in the H2O 2.7 mu m band can be cl early resolved by the SWS and is identified in an early M giant, whose photosphere will never produce H2O. This is definite evidence for H2O of non-photospheric origin in an early M giant. Also, the observed H2 O and CO2 bands in a late M giant are too strong to be explained by a photospheric origin alone. Further, the H2O 2.7 mu m band is found in four early M supergiants in the h + chi Persei clusters (three of whic h show UIRs) and is especially strong in the M4 supergiant S Per (whic h also shows a highly peculiar SED). Thus, against a belief that H2O i s found only in the latest M giants such as Miras, the SWS has reveale d the presence of H2O in a wider region of the HR diagram. The origin of this H2O is unknown but is probably in a non-photospheric extra env elope. Such a H2O envelope appears to be a general feature through ear ly M (super)giants to cool supergiants such as S Per, where the envelo pe has finally developed to be optically thick.