A Laboratory Measurement of Meteor Luminous Efficiency

Abstract

Luminous efficiency, as defined in meteor theory, has been determined by measuring the radiant energy from luminous trails produced by injecting high-velocity, sub-micron-diameter, iron particles into gaseous targets. The high-velocity particles were obtained from an electrostatic particle accelerator, and the velocity and mass of each particle were measured prior to entering the gas. Particle velocities ranged from about 15 to 40 km/sec. In this velocity range, the particles are completely vaporized while suffering small deceleration, which is also the case for most natural meteors. The radiant energy from the trail was determined by means of a calibrated photomultiplier tube. The luminous efficiency in the spectral band 3400-6300 A for an air target and iron particles was found to be nearly constant over the velocity interval 20-40 km/sec. The (dimensionless) luminous efficiency in this velocity range is about 0.005. Spectral measurements indicate that the gross spectrum of the emitted light does not change markedly with velocity, and therefore the experiments provide a good measure of the velocity dependence of the luminous efficiency. With certain assumptions concerning the spectrum which are detailed in the text, the measured value of the luminous efficiency for iron particles in air is 3 9 X 1O'~ (cgs and Mpg) for 3700 «= X «= 6300 A. This value is a factor of 2 or 3 lower than that reported by other workers