Aims. The complex study of millimetre-sized meteoroids can reveal more about the structure and origin of population of these meteoroids. Methods. Double-station video observations, paired with spectroscopic video observations, were used to study small meteoroids. In total 152 sporadic and shower meteors of maximum brightness between magnitude −5 and +3 were analysed. Spectral classification was based on time-integrated intensities of lines of Na, Mg, and Fe. Meteor light curves and deceleration were fitted by the grain erosion model. Heliocentric orbits of all meteors were computed. Monochromatic light curves were constructed in order to study differential ablation. The length of meteor wakes was evaluated as well.Results. The variety of properties among millimetre-sized meteoroids proved different sources and histories of this material. Meteoroids that contain small grains tend to release their sodium early. For given grain sizes, the sodium in Na-poor meteoroids is released earlier than in meteors without sodium depletion. Overall, meteoroids with sodium depletion are revealed to have different structures: they have stronger material without very small grains and they do not show very bright wakes. Two iron meteoroids on Halley-type orbits were observed, thereby supporting the idea of large-scale mixing of material in the early solar system. The distribution of grain sizes of Jupiter-family members was in good agreement with results from the COSIMA instrument on the ROSETTA probe.

Aims. We present a library of low-resolution meteor spectra that includes sporadic meteors, members of minor meteor showers, and major meteor showers. These meteors are in the magnitude range from +2 to −3, corresponding to meteoroid sizes from 1 mm to 10 mm. Methods. Parallel double-station video observations allowed us to compute heliocentric orbits for all meteors. Most observations were performed during the periods of activity of major meteor showers in the years between 2006 and 2012. Spectra are classified according to relative intensities of the low-temperature emission lines of Mg, Na, and Fe. Results. Shower meteors were found to be of normal composition, except for Southern δ Aquariids and some members of the Geminid shower, neither of which have Na in the meteor spectra. Variations in Na content are typical for the Geminid shower. Three populations of Na-free mereoroids were identified. The first population are iron meteorites, which have an asteroidal-chondritic origin, but one meteoroid with low perihelion (0.11 AU) was found among the iron meteorites. The second population were Sun-approaching meteoroids in which sodium is depleted by thermal desorption. The third population were Na-free meteoroids of cometary origin. Long exposure to cosmic rays on the surface of comets in the Oort cloud and disintegration of this crust might be the origin of this population of meteoroids.

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Context. A significant fraction of small meteors are produced by iron meteoroids. Their origin and the interaction with the atmosphere have not been well explained up to now. Aims. The goals of the study are to observe faint, slow, low altitude meteors, to identify candidates for iron meteoroids among them, to model their ablation and light curves, and to determine their properties. Methods. Double station video observations were used for the determination of atmospheric trajectories, heliocentric orbits, light curves, and spectra of meteors. Meteors with iron spectra or of suspected iron composition based on beginning heights and light curves were modeled. The immediate removal of liquid iron from the surface as a cloud of droplets with Nukiyama–Tanasawa size distribution and their subsequent vaporization was assumed as the main ablation process on the basis of our previous work. The numerical model has only five parameters: meteoroid initial velocity v∞, zenith distance z, initial mass m∞, mean drop size Ddr, and luminous efficiency τ. The theoretical light curves were compared with the observed ones. Results. The model is able to explain the majority of the selected light curves, and meteoroid parameters that are not directly observable – m∞, Ddr, and τ – are determined. Unlike in most meteor studies, the mass and luminous efficiency are determined independently. Luminous efficiency ranges from 0.08 to 5.8%; it weakly decreases with increasing initial meteoroid mass. No simple dependency on initial velocity was found. The mean size of iron drops depends on the meteoroid velocity. Slower meteoroids can produce drops with a wide range of mean sizes, whereas faster ones are better matched with larger drops with a smaller dispersion of sizes.