| Research Abstract |
1. From the analysis of ISO SWS spectra, supplemented with those from the ISO data archive, we show that water exists throughout red (super)giants including K giant a Tau (Aldebaran), early M supergiants a Ori (Betelgeuse) & μ, Cep, and all the M 'giants of MOIII - M9III Water was discovered in α Ori & μ Cep nearly 40 years ago by the pioneering space mission with Stratoscope II, but this important discovery was so unexpected at that time (and even today) that it has been misinterpreted and overlooked for a long time. We rediscovered this unexpected phenomenon and extended it to a larger sample of cool luminous stars. The excitation temperatures of the water bands are rather high (T_<ex> 【approximately equal】 1800K) and water appears in emission in μ, Cep as well as in late M giants. This finding is difficult to understand by the presently known models and/or theories on stellar atmospheres, and we propose instead the presence of a warm molecular sphere (MOLsphere) as the 4-th componen
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t of the stellar atmosphere consisting of the photosphere, chromosphere, and expanding cool wind. How to understand the origin of the MOLsphere and its physical structure should be a challenge to the theory of 'stellar atmosphere.
2. We observed some spectra of M dwarfs by ISO, but we must wait for the next infrared missions such as Astro-F (ISAS) and SIKTF (NASA) to observe the spectra of brown dwarfs. To provide physical basis of interpreting the infrared spectra of cool dwarfs including M-type and brown dwarfe, we developed model photospheres of cool dwarfe, in which formation of dust cloud plays a crucial role. Based on a simple thermodynamical argument, we proposed unified cloudy model (UCM) in which dust can be sustained in the temperature range between the condensation temperature (T_<cond> 【approximately equal】 2000K) and the critical temperature・ (T_<cr> 【approximately equal】 1800K), independently of T_<eff>. Then, the dust cloud appears in the optically thin region in L dwarfe whose Teff are relatively high but will sink below the observable photosphere in the cooler T dwarfe. The observed CM diagram, SED, and spectra are well reproduced with our UCMs consistently throughout L to T dwarfe. This fact in turn can be regarded as an observational confirmation of our model of the cloud formation. We hope that our UCM will be of some clue for modeling the atmospheres of extrasolar giant planets. Less
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