Experimentally determined luminous efficiency measurements applied to photometric meteor masses

Material deposited by meteors ablating in the upper atmosphere can have significant effects on atmospheric dynamics, via changed densities, conductivities, and compositions. Characterizing and constraining this input is important for understanding the mesosphere/lower thermosphere (MLT) and the E region ionosphere and correctly modeling large scale dynamics. However, mass flux estimates calculated using different techniques vary widely. Many methods of measuring this parameter exist, each with associated biases and errors. The result is a discrepancy of several orders of magnitude in determinations of the total meteor mass flux. This work focuses on an effort to make improved measurements of one physical property, the luminous efficiency, using laboratory experiments, and to apply the results to observed optical meteors in order to calculate photometric masses.

The luminous efficiency characterizes the fraction of a meteor’s kinetic energy that is converted into light output during ablation. This property has been measured in the lab and determined from observations, with large variation in the results (Subasinghe 2019). To improve luminous efficiency estimates, we use the dust accelerator at the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT) at the University of Colorado. We have modified a gas ablation target (used previously by Thomas et al. 2016 to measure the ionization coefficient) to include a more advanced optical system and a high-speed data acquisition system, which measures the light output of a dust particle as it ablates with high spatial and temporal resolution. We have conducted two data collection campaigns to study iron and aluminum dust particles, and have observed more than 1,300 ablation events. By combining this data with the measured masses and velocities of the original particles, we can determine the luminous efficiency for a wide range of speeds and particle masses.

These experimental results can then be applied to optical observations. We calculate photometric masses for a set of 150 meteors observed by a camera network in Norway. These meteors were observed simultaneously by the MAARSY radar, allowing us to calculate radar masses independently. We present masses determined from both systems and compare the results to make an overall mass estimate, constrain the error in the mass, and provide insight into the discrepancy between radar and photometric masses.