J. Borovicka (Ondrejov Observatory, Czech Republic), R. Stork (Ondrejov Observatory), J. Bocek (Ondrejov Observatory)

          We report the results of a low resolution meteor spectroscopy experiment performed during the 1998 international Leonid Multi-Instrument Aircraft Campaign. A video camera with image intensifier and spectral grating was run onboard the FISTA aircraft flying over the eastern Pacific on November 17, 1998, 15-21 UT. During this time, a secondary maximum of the Leonid shower with zenith hourly rate of about 200 occurred (Arlt R., WGN 26, 239, 1998). The maximum was rich in relatively faint meteors and is believed to consist of material ejected from the parent comet Tempel-Tuttle relatively recently. During the 6 hours of observations, 119 meteor spectra were recorded, at least 98 of them being Leonids. The meteor magnitudes range from -5 to +3, the dispersion is 1.2 nm/pixel in the first order and the wavelength coverage is 380-880 nm, with maximum sensitivity near 550 nm. The Leonid spectra obtained in this experiment were compared with spectra of Perseids and other meteors obtained with a sensitive TV camera at the Ondrejov observatory in the recent years.

          Leonid spectra were found to be very rich in lines of oxygen, nitrogen and nitrogen molecule. About 2/3 of radiated energy in the given wavelength range is due to atmospheric emissions. This can be ascribed to the large velocity of Leonid meteors. About 1/6 of the energy is radiated as thermal continuum and only another 1/6 is due to the emissions of the meteoric vapor. Only the lines of Mg, Na, Fe, and Ca are bright enough to provide information on meteoroid composition. Their relative abundances are, within the errors, consistent with normal solar system abundances. However, another effect was found in Leonids which is not present in Perseids: The sodium line is relatively bright at the beginning but almost disappears at the middle of the trajectory. The effect is less pronounced in bright meteors than in faint meteors and suggests that Leonid meteoroids are very loose and can be described in terms of the dustball model (Hawkes and Jones, MNRAS 173, 339, 1975). Small meteoroids disintegrate completely before the onset of ablation and volatile sodium material is therefore released from the whole volume and can evaporate substantially earlier than silicate grains. A search for organic carbon bearing molecules in Leonid spectra yielded no convincing detection.