On the sodium enhancement in spectra of slow meteors and the origin of Na-rich meteoroidsOPEN ACCESS 

Pavol Matlovič, Juraj Tóth, Leonard Kornoš, Stefan Loehle

In Press, Journal Pre-proof, Available online 22 April 2020




• The effect of speed dependency on the measured Na/Mg intensity ratio in slow meteors is the dominant effect causing false identification in numerous Na-enhanced and Na-rich meteoroids.
• Na-rich spectra were observed during laboratory simulated ablation of meteorite samples tested at similar conditions irrespectively of the meteorite composition.
• Majority of meteoroids previously identified as Na-rich represent asteroidal bodies moving on Apollo-type orbits and are most probably of common chondritic composition.
• New speed-dependent boundaries for the classification of Na-enhanced and Na-rich meteoroids are defined.
• Real compositional Na-enhancement is revealed in five cometary meteoroids including members of major meteoroid streams.”

“The detected Na/Mg ratio in a sample of 17 Na-enhanced and Na-rich meteors is investigated based on obtained spectral, orbital and structural data. We utilize the meteor observations of the AMOS network obtained within a survey of medium-sized meteoroids supplemented by higher-resolution spectra observed on the Canary Islands. Ground-based meteor observations are then compared with high-resolution Echelle spectra of simulated ablation of known meteorite samples in a high-enthalpy plasma wind tunnel. It was found that most Na-enhanced and Na-rich spectra can be explained by the effect of low meteor speed related to low ablation temperatures and generally do not reflect real meteoroid composition. Spectra obtained by the laboratory experiment simulating low meteor speeds show corresponding Na-rich profiles irrespectively of the meteorite composition. We estimate that for an H-type ordinary chondrite with speed of ≈10 km s-1, the Na line intensity is increased by a factor of 40 to 95. The dynamical analysis has revealed that all Na-rich meteors originated on Apollo-type orbits and exhibit consistent chondritic material strengths. For more clarity in the classification of Na-enhanced and Na-rich meteoroids, we propose new speed-dependent boundaries between the spectral classes. Real compositional Na enhancement was confirmed in five cometary meteoroids: two Perseids, a α-Capricornid, v-Draconid and a sporadic. The two Na-enhanced Perseids were linked with increased material strength suggesting that the detected increase of volatile content has implications for the meteoroid structure.”