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Astron. Astrophys. 337, 591-602 (1998)

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6. Conclusions

Theoretical spectra of radiation from a [FORMULA]1 meter size H-chondrite meteoroid penetrating the atmosphere at the altitudes of 60-25 km were presented. The spectra are based on the ablating piston model by Golub' et al. (1996a) with improved spectral opacities. The spectra in the wavelength range 4500-6600 Å were compared with the observed spectra of the very bright Beneov bolide EN 070591.

Both the theoretical spectra and the observed spectra have shown that the bolide radiation is composed of atomic line emissions, molecular bands and a continuous radiation. The role of the continuum relative to the lines increases with increasing meteoroid size and decreasing altitude. This is the reason why the continuum is negligible in fainter meteors.

The total radiated intensity in the given passband as well as the shape of the spectrum confirm that the Beneov meteoroid was already fragmented at an altitude of 40 km. This is in agreement with the conclusion of Paper I, where the bolide dynamics and light curve were analyzed.

The atomic lines are produced under an effective excitation temperature of 4000-6000 K in both theoretical and observed spectra. The observed spectrum also contains lines of Si II and N II which must be produced under substantially higher temperatures. These lines are not present in the theoretical spectra although a high temperature region is present in the model. This is due to the fact that the radiation from the hot region is absorbed by the cooler vapors in the model.

The intensities of the lines forming the [FORMULA] 5000 K radiation are different in the theoretical model and in the observation. The lines of Fe I are too faint and the lines of Ca I are too bright in the model. Also the continuum level is larger in the model. These differences can be explained by the fact that the vapors are confined in too small volume and under too large density in the model in contrast to the reality. The larger expansion of vapors than predicted is probably a consequence of mutual interaction of fragments and a more complicated ablation process of individual fragments. These effects are to be considered in future modeling.

The theoretical spectra predict that a large part of energy is radiated in the infrared part of the spectrum, especially by the bands of hot air. This could not be confirmed because infrared spectra of Beneov are not available. In the visible region atmospheric emissions are neither predicted nor observed (except for the peculiar N II lines). Similarly, it could not be definitely resolved whether the observed continuum is produced by the vapors or the air.

In summary, we presented the first detailed comparison of a purely theoretical radiative-hydrodynamic spectral model and the observed spectrum of a bolide. The spectra generally agree in respect to the presence of continuous radiation and atomic and molecular emissions. The effective temperature of the atomic emissions and the shape of the continuum are nearly the same. Details of the spectra differ and this is a consequence of poorly known details on the energy transport, ablation, and fragment interaction. Nevertheless, together with the modeling in Paper I, we obtained a consistent picture of the Beneov bolide, including its mass, dynamics, fragmentation and radiation.

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© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998
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