AURORAL LYMAN-ALPHA AND H2 BANDS FROM THE GIANT PLANETS .1. EXCITATION BY PROTON PRECIPITATION IN THE JOVIAN ATMOSPHERE

This paper is part of a work aimed at modeling the ratio of the observ ed Jovian auroral intensity at H Lyman alpha and in the H-2 Lyman and Werner bands and interpreting them as diagnostic of the incident magne tospheric particle species and energy. The work is planned in three st eps: (1) modeling of the volume excitation rate, (2) modeling of the r adiative transfer at Lyman alpha, (3) application to existing observat ional data and new data obtained from the Hubble Space Telescope. The present paper deals with the first step. Models of the volume excitati on rate have previously been developed for low energy electrons and ox ygen ions. However, the energy range of the study has to be extended t owards higher energy in view of recent results on the penetration dept h of the primary particles. Protons have not been modeled so far. We h ave used an existing electron code of degradation of energy [Gerard an d Singh, 1982] which has been improved, updated and adapted to the caw of precipitating protons. The issues of nonequilibrium beam H/H+ frac tions and of getting reliable cross sections over a wide energy range have been considered with particular. care. The altitude distribution of the volume excitation rate is compared for electrons and protons, f or various initial energies in the range 10-50 keV and 50 keV to 1 MeV , respectively.