Quantitative meteor spectroscopy: Elemental abundances

Procedures are outlined to derive from a meteor spectrum the elemental abundances of its meteoroid, with particular application to observations obtained by an unintensified cooled-CCD slit-less spectrograph. Results are given for two Leonid meteors observed during the 2001 encounter of Earth with dust ejected by comet 55P/Tempel-Tuttle in 1767. The spectra contain air plasma lines of N and O, and meteoric metal atom lines of Fe, Mg, Na, Ca, Si, Mn, Al, and Cr. Excitation conditions are investigated from the relative line intensity of Fe and N+ lines. The elemental abundances, normalized to solar system abundances, show a striking correlation with condensation temperature, defined as the temperature at which 50% of elements in a cooling gas mixture with chondritic abundance have condensed into a solid phase. Iron is depleted by a factor of 3, magnesium, calcium, and aluminum by a factor of 8. I conclude that rapid evaporation keeps the mineral surface temperature at ∼1150 K. Much of the refractory elements in these fast 71.6 km/s Leonid meteoroids are deposited in the form of solid meteoric debris rich in Mg, Ca, and Al.