Atmospheric structure and the mass loss process in Miras

Kenneth Hinkle & Thomas Lebzelter

NOAO, USA

The presence of a molecular absorption layer visible in the infrared spectra of Miras was first noted more than 30 years ago. Both the temperature and velocity of this region is significantly different than that of the stellar photosphere. We explore the relation of this region of the stellar photosphere by using a decade long time-series of Mira K and H band spectra. The velocities and strengths of CO and H₂O lines show that the molecular layer is time variable. The velocities are related to the cyclic Mira pulsation but vary aperiodically and on a longer time scale. We discuss the relation of the molecular layer to the stellar photosphere, the circumstellar region, mass loss, and the dust formation process.

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