Coordinated Optical and Radar Measurements of Low Velocity Meteors

TL;DR

This study combines optical and radar measurements of low velocity meteors to estimate luminous efficiency and ionization coefficients, revealing a wide range of efficiencies and correlations with radiant power.

Contribution

It provides the first simultaneous optical and radar measurements of low velocity meteors, offering new insights into luminous efficiency and ionization processes.

Findings

Luminous efficiency averages 0.6% at low speeds.

No clear trend of efficiency with speed observed.

Approximately 20% of meteoroids are probable iron types.

Abstract

To better estimate which luminous efficiency ($\tau$) value is compatible with contemporary values of the ionization coefficient ($\beta$), we report a series of simultaneous optical and specular echo radar measurements of low speed meteors. A total of 1249 simultaneous EMCCD and radar meteors were identified. A subset of 36 events were analyzed in detail, with 29 having speed less than 20 km/s. These meteors had G-band magnitudes at the specular radar point between +4 and +7.7, with an average radiant power of 5W (assuming a 945 W power for a zero magnitude meteor) and masses of 1 - 10 mg. These correspond to a typical magnitude of +6. We find that $\beta$ / ${\tau}$ strongly correlates with radiant power. All our simultaneous meteors had asteroidal-like orbits and six were found to be probable iron meteoroids, representing 20 percent of our slow velocity sample. Luminous efficiency values averaged 0.6% at low speed, ranging from less than 0.1% to almost 30%. No trend of luminous efficiency with speed was apparent, though a weak correlation between higher values of luminous efficiency and radiant power may be present.