Scientists: J. Borovicka Z. Ceplecha P. Pecina M. Simek R. Stork PhD Student: P. Koten Assistants: J. Bocek H. Ceplechova J. Florian J. Keclikova A. Kolar O. Mikulastik D. Novakova P. Pridal

 

The group observes meteors in the optical region and by meteor radar, and performs theoretical interpretations of the observations. The basic observational system is the European Fireball Network established in 1963 and now consisting of 10 stations in the Czech Republic and several tens of stations in Austria, Belgium, Germany, the Netherlands, Slovakia and Switzerland. Fireballs brighter than magnitude -5 are observed and their atmospheric and heliocentric trajectories are computed. Fireball spectra are simultaneously photographed at the Ondrejov Observatory. Sensitive television cameras are used to observe faint meteors and their spectra during meteor shower activity. Selected meteor showers are studied by meteor radar and the data of shower activity profiles now cover several decades. Simultaneous radar and television observations are also being performed.

The observational data are used to study the physical processes during the penetration of meteoroids into planetary atmospheres, including radiation, ionization and meteoroid fragmentation. The physical properties and chemical composition of different types of meteoroids, their origin and distribution in the solar system and their relation to comets, asteroids and meteorites are being determined. The members of the group have developed a variety of methods for these purposes. At the present time, most attention is devoted to the meteors of the Leonid meteor shower which has been very active since 1998. The members of the group participated in several international airborne and ground based campaigns to observe the shower and obtained rich photographic and video data including spectroscopy. The Ondrejov radar provided additional data. The analysis of the data yielded not only information on the shower activity profile and meteor trajectories, orbits, light curves and spectra, but also quite new discoveries on meteor radiation up to the altitude of 200 km and on meteor differential ablation. Other activities include precise dynamical studies of photographically observed bolides, the study of the Moravka meteorite fall in May 2000, and the analysis of some other superbolides.

Recent results:

Differential ablation of sodium atoms in faint Leonid meteors was discovered using the video spectroscopy. The sodium line appears earlier than other meteoric lines (magnesium, iron, calcium) and disappears at the time when the other lines are still quite bright. We interpret this fact in the framework of the dust ball model of Hawkes and Jones. Sodium appears to be a part of relatively volatile glue which holds together silicate grains. The glue evaporates soon and the grains then continue their flight individually. This effect is typical for Leonids but is present in some other meteors, too.

The first video spectra of meteor persistent train were obtained during the 1999 airborne Leonid campaign. The spectra enabled us to derive the temperature in the first seconds of the train formation. The temperature dropped from 5000 K to 1200 K during two seconds. Due to the low density and strong radiation, Boltzmann populations of atomic levels were not maintained in the train. The radiation of hot dust (1400 K) was also detected. The train persistent luminosity, however, was produced by a yellow continuum which we tentatively identified with the NO₂ molecule.

Basic equations of motion and ablation of a single non-fragmenting body through the atmosphere were solved with ablation and shape-density coefficients as general functions of time. This solution was applied to 22 photographically recorded meteoroids with very precise data available, such meteoroids which have not yielded solutions by using the gross-fragmentation model. Extremely high values of the shape density coefficient, K, at the early parts of the luminous trajectory are the main reason for non-existing gross-fragmentation solutions. Reasons for such high values of K are examined in some detail, including analysis of spectral records available for one of the meteoroids. Also positive values of acceleration well outside standard deviations were documented for several meteors. Such cases cannot be interpreted by our model. We suspect that electric forces originating from the atmospheric charges and from meteoroid charges (which were not included in the drag equation) are responsible for the observed very high values of the shape-density coefficient at the early parts of meteoroid trajectories.

The dependence of sporadic meteor echo rates on the phase of the solar cycle represented by the Relative Sunspot Number during the period 1958-1997 revealed that the highest meteor activity follows the culmination of solar cycle by 1.15 +- 0.56 years for T > 1 sec and by 1.45 +- 0.47 years for echoes with T > 8 sec, contrary to previously published results. The 1998 and 1999 radar observations of the Leonid stream in Ondrejov revealed that while the 1998 activity was due to large particles the 1999 activity was caused by faint those, quite in accord with the results of optical observations performed worldwide.
 
 

TV Meteor Spectra

Comet 1996 B2 Hyakutake with meteor