Photoionization of the circumstellar shell of betelgeuse by chromospheric radiation

The occurrence of a chromosphere can have a profound effect on the cool circumstellar envelope surrounding a star such as α Ori. Passage of a wind through the warm, partially ionized chromosphere reduces the gas to atoms or atomic ions. The dominant ion in the chromosphere is H+, which recombines when photoionization from excited states freezes out. The gas does not become neutral, however, because the chromospheric UV radiation is sufficiently strong to maintain a significant fraction of the heavy ions almost fully ionized throughout the bulk of the CS shell. The authors have analyzed the physical processes which enter into the dynamic balance between photoionization and recombination in the CS shell of α Ori by solving appropriate time-dependent equations which generalize the original treatment of this problem. In addition to describing the physical processes affecting the ionization of the CS shell, they present preliminary results on the interpretation of the measured spatial profile of the KI density and on the determination of the mass loss rate