Water Observed in Red Giant and Supergiant Stars - Manifestation of a   Novel Picture of the Stellar Atmosphere or else Evidence against the   Classical Model Stellar Photosphere
  We detected the H2O 6.3 micron bands in more than 30 normal red giants stars from K5III to M8III as well as in some early M supergiants on the SWS spectra retrieved from the ISO Data Archive. This result, however, shows serious inconsistency with the present model photospheres which predict H2O only in the latest M (super)giant stars. Also H2O was once discovered in the early M (super)giant stars nearly 40 years ago with the balloon-borne telescope named Stratoscope II. This discovery was so unexpected at that time that it was not understood correctly and overlooked for a long time. Now, we reflect on our ignorance of this important discovery during the 40 years and should consider more seriously the meaning of the rediscovery of water in so many red (super)giant stars with ISO. In view of the detection of H2O in emission in the early M supergiant mu Cep as well as in late M giants with ISO, H2O should be in the outer atmosphere rather than in the photosphere. We propose that the absorption as well as emission of H2O should be originating in a new component, which we refer to as molecular sphere. Since the extend atmospheres of red (super)giants radiate efficiently in the infrared, it is not surprising if the true structure of the atmospheres of these stars can first be revealed with the infrared observations especially from space. 
Takashi Tsuji