Ionic Spectra of Meteors

A two-step ionization and excitation model is proposed as an alternative mechanism to the commonly accepted direct-excitation one for the generation of ionic meteor spectra. A near-resonance criterion is invoked to indicate when this mechanism is expected to predominate. The implications of the model are calculated in a slip-flow "threshold" approximation. That is, first and second collisions of atmospheric molecules as well as first collisions of vapor atoms are taken into account. Qualitative agreement with observations is obtained. The model is then applied specifically to the example of the bright Ca ii spectra, which are enhanced by this mechanism over the direct-excitation mode.