Spectral and orbital survey of medium-sized meteoroids

Aims. We investigate the spectra, material properties, and orbital distribution of millimeter- to decimeter-sized meteoroids. Our study aims to distinguish the characteristics of populations of differently sized meteoroids and reveal the heterogeneity of identified meteoroid streams. We verify the surprisingly large ratio of pure iron meteoroids on asteroidal orbits detected among mm-sized bodies. Methods. Emission spectra and multi-station meteor trajectories were collected within the AMOS network observations. The sample is based on 202 meteors of -1 to -14 magnitude, corresponding to meteoroids of mm to dm sizes. Meteoroid composition is studied by spectral classification based on relative intensity ratios of Na, Mg, and Fe and corresponding monochromatic light curves. Heliocentric orbits, trajectory parameters, and material strengths inferred from empirical K-B and P-E parameters were determined for 146 meteoroids. Results. An overall increase of Na content compared to the population of mm-sized meteoroids was detected, reflecting weaker effects of space weathering processes on larger meteoroids. The preservation of volatiles in larger meteoroids is directly observed. We report a very low ratio of pure iron meteoroids and the discovery of a new spectral group of Fe-rich meteors. The majority of meteoroids on asteroidal orbits were found to be chondritic. Thermal processes causing Na depletion and physical processes resulting in Na-rich spectra are described and linked to characteristically increased material strengths. Numerous major and minor shower meteors were identified in our sample, revealing various degrees of heterogeneity within Halley-type, ecliptical, and sungrazing meteoroid streams. Our results imply a scattered composition of the fragments of comet 2P/Encke and 109P/Swift-Tuttle. The largest disparities were detected within alpha-Capricornids of the inactive comet 169P/NEAT and delta-Aquarids of the sungrazing 96P/Machholz. We also find a spectral similarity between kappa-Cygnids and Taurids, which could imply a similar composition of the parent objects of the two streams.