Symmetrical Chemi‐Ionization and Chemi‐Recombination Processes in Low‐Temperature Layers of Helium‐rich DB White Dwarf Atmospheres

The influence of symmetrical chemi-ionization and chemi-recombination processes on the helium atom Rydberg states' population in weakly ionized layers of helium-rich DB white dwarfs has been investigated. The ionization processes in He ðn Þþ Heð1s2Þ collisions and their inverse recombination processes Heþ 2 þ e and Heð1s2 Þþ Heþ þ e have been considered in domains of principal quantum numbers n 3 and tempera- tures 12; 000 KTeff 30; 000 K. These processes have been treated within the frame of the semiclassical theory developed earlier. Their contributions to the Rydberg state populations have been compared with electron-electron-ion recombination, electron-excited atom ionization, and electron-ion photorecombina- tion processes. Results showed that these processes can be dominant ionization/recombination mechanisms in helium-rich DB white dwarf atmosphere layers for log g ¼ 7 and 8 and Teff 20; 000 K and have to be implemented in relevant models of weakly ionized helium plasmas. Subject headings: atomic processes — stars: atmospheres — white dwarfs