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Published online by Cambridge University Press: 12 April 2016
The origin of mass-loss in cool luminous stars is still obscure; several known mechanisms such as thermally driven wind, radiation-driven wind(via dust), wave-driven wind etc all have serious difficulties, if examined in the light of recent observations. At the same time, recent observations in the infrared and radio spectral domains revealed that outer envelope of red (super)giant stars has highly complicated spatial and velocity structures, while inner envelope may have new component that had not been recognized before. For example, recent high resolution infrared spectroscopy revealed a possible presence of a quasi-static turbulent molecular dissociation zone somewhere in the outer atmosphere. This new component may represent a transition zone between the warm chromosphere and the huge expanding molecular envelope, and may be a cool component of chromospheric inhomogeneity or a moleclar condensation in a cool corona extended by turbulent pressure. Such a result can be regarded as observational evidence in support of a recent theory of autocatalytic molecular formation by thermal instability due to molecular cooling. Thus, observation and theory consistently show the presence of a new component - quasi-static turbulent molecular formation zone - in outer atmosphere of cool luminous stars, and a possibility of a unified understanding of outer atmospheric structure and mass-loss, in which turbulence may play important role, can be proposed.