Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...279..627b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 279, no. 2, p. 627-645
Astronomy and Astrophysics
Astrophysics
71
Ablation, Abundance, Bolides, Gratings (Spectra), Least Squares Method, Mathematical Models, Photographs, Spectrum Analysis, Chemical Composition, Light Curve, Spectrographs, Visible Spectrum
Scientific paper
A grating spectrum (45 A/mm) of a fireball of -9th absolute magnitude and velocity of 18 km/s has been analyzed. A new simple model for meteor spectra has been developed. Thermal equilibrium is assumed and self-absorption is taken into account. The free parameters of the model are the temperature, the column density of Fe I atoms, the relative abundances of other atoms, and the visible surface area of meteor radiating volume. The synthetic spectrum based on this model was computed and compared with the observed spectrum. The values of the free parameters were calculated by the least squares method. Then the abundances of neutral atoms were corrected for ionization to obtain the true ratios of chemical elements. The abundances of Fe, Na, Mg, Ca, Ti, Cr, Mn, Ni, and Al were determined such way. The computations were performed independently at 43 points along the fireball trajectory between heights of 57-35 km. It was found that thermal equilibrium was relatively well satisfied at the heights below 50 km. The temperature varied on the range 3500-4700 K. But there is also a spectral component with temperature of about 10,000 K in the spectrum. This component consists of a few lines of Mg II, Si II and Fe II and originates probably in the shock wave. The chemical composition of the radiating gas varied along the fireball path and does not reflect the chemical composition of the meteoroid itself. The refractory elements (Al, Ca, Ti) are underabundant in the gas. The material was ablated by melting in liquid phase and then evaporated in surrounding hot gas, but the refractory (low melting) elements were evaporated incompletely or too late. About 95% of the hot gas around the meteoroid were formed by the air.
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