Meteor radiation, ionization and atomic luminous efficiency

Abstract

Meteor radiation consists predominantly of line emission, due to impact excitation of the meteor atoms. Recombination of atomic ions is another, probably minor source of radiation. Most of the molecules are broken up by collisions. Redistribution of charge effectively removes all ions of higher order whose ionization potentials exceed those of the atmospheric molecules. In the last stage of deceleration of an atomic ion it will have a fair chance of capturing a charge from an air molecule, without being able to become ionized again. Further, most of the ions are molecular, produced by redistribution of charge; their life-time is relatively short, as would correspond to radiationless dissociative recombination. It is shown that King’s estimates of arc intensities should be used as straightforward intensities. Using the observed arc intensities for Fe I and Fe II, and approximate theoretical pro­cedures for other atoms, luminous efficiencies in the photographic, visual and red regions of the spectrum, as well as in certain selected multiplets, are calculated for the excited states of atoms and ions which are common in meteors. It is found that meteor iron and stone possess practically the same visual luminous efficiency per unit mass, equal to 60% of the efficiency assumed in former publications of the writer. The coefficients of radiative attachment and luminous efficiencies in recombination are calculated for the more important ions, using an order-of-magnitude procedure. The absolute luminous efficiency per recombination is about 6 times greater than that per excitation of the neutral atom, the ratio being the same for iron as for stone.