John Greaves points our attention at a recently published meteor related paper:
Coordinated Optical and Radar measurements of Low Velocity Meteors
This article has been submitted for publication by Peter Brown and Robert J. Weryk.
Abstract: To better estimate which luminous efficiency (τ) value is compatible with contemporary values of the ionization coefficient (β), we report a series of simultaneous optical and specular echo radar measurements of low speed (v < 20 km/s) meteors. We focus on the low speed population as secondary ionization is not relevant and the initial trail radii are small, minimizing model assumptions required to estimate electron line density. By using the large decrease in expected ionization coefficient at such low speeds, we attempt to better define the likely ratio of photon to electron production. This provides an estimate of the probable luminous efficiency, given that recent lab measurements of ionization efficiency agree with established theory (Jones, 1997; DeLuca et al., 2018) suggesting β is more constrained than τ.
Optical measurements were performed with two pairs of autonomously operated electron-multiplied charge coupled device cameras (EMCCDs) co-located with the multi-frequency Canadian Meteor Orbit Radar (CMOR) (Brown et al., 2008). Using the timing and geometry of individual meteors measured by both the radar and multi-station EMCCD systems, the portion of the optical lightcurve corresponding to each specular radar echo is measured and the received echo power used to estimate an electron line density. A total of 1249 simultaneous EMCCD and radar meteors were identified from observations between 2017 – 2019 with 55 having in atmosphere speeds below 20 km/s. A subset of 36 events were analyzed in detail, with 29 having speed < 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). These correspond to a typical magnitude of +6. Following the procedure in Weryk & Brown (2013b), the ratio of electron line density (q) to radiant power (I) provides a direct estimate of the ionization coefficient (β) to luminous efficiency (τ) ratio for each event. We find that β / τ strongly correlates with radiant power. All our simultaneous meteors had asteroidal-like orbits and six were found to be probable iron meteoroids, representing 20% of our slow < 20 km/s sample. Luminous efficiency values averaged 0.6% at low speed, ranging from < 0.1% to almost 30%. No trend of luminous efficiency with speed was apparent, though a weak correlation between higher values of τ and radiant power may be present.
You can download this paper for free: https://arxiv.org/pdf/2007.04200.pdf (43 pages).
Older meteor library news:
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