EMISSION OF HEH+ IN NEBULAE

The formation and destruction processes of HeH+ in nebulae are discussed, and calculations of the abundances of HeH+ are presented. It is shown that for effective temperatures of the ionizing source exceeding 50,000 K, the abundances are of the order of 10(12) cm-2, largely independent of the nebular parameters. The emission-line intensities increase approximately as the density of the nebula. Results are given for two detailed models of the planetary nebula NGC 7027. The predicted intensities exceed the observational upper limit. The emissions have sharply peaked distributions with maximum intensity reached in a narrow zone at the edge of the ionized region. The greater art of the emission may be outside the region observed.