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Spectra of meteors and meteor trains. Ji ří Borovička Department of Interplanetary Matter. Meteor photograph. All-sky image. Kouřim bolid e (– 13 mag). Bolid e – 18 mag. Double-station video meteor. Meteor speeds. 11 – 73 km/s Faint meteors: 110 – 80 km Fireballs: 200 – 20 km.

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Spectra of meteors and meteor trains


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    Presentation Transcript
    1. Spectra of meteors and meteor trains Jiří Borovička Department of Interplanetary Matter

    2. Meteor photograph

    3. All-sky image Kouřim bolide (– 13 mag)

    4. Bolide – 18 mag

    5. Double-station video meteor

    6. Meteor speeds 11 – 73 km/s Faint meteors: 110 – 80 km Fireballs: 200 – 20 km Meteor heights

    7. HIGH RESOLUTION PHOTOGRAPHIC SPECTRA OF FIREBALLS

    8. Battery of six photographic grating cameras with rotating shutter in Ondřejov

    9. Example of a photographic prism spectrum of a bright Perseid meteor

    10. Detail of the prism spectrum

    11. Example of photographic grating spectrum of a slow sporadic fireball zero order first order second order

    12. detail of grating spectrum

    13. Detail of a Perseid spectrum almost head-on meteor blue part shown (3700–4600 Å)

    14. Radiative transfer in spectral lines

    15. Assuming thermal equilibrium

    16. Emission curve of growth

    17. Model assumptions • The radiation originates in a finite slab of gas (plasma) with a cross section P • Atomic level population is described by the Boltzmann law for an excitation temperature T • Self-absorption is taken into account (the gas is not optically thin)

    18. Free parameters • Excitation temperature, T • Column densities of observable atoms, Nj • Meteor cross-section, P • Damping constant, 

    19. Total number of Fe atoms

    20. Temperature

    21. Cross-section

    22. Electron density

    23. Two components in meteor spectra • The spectra can be explained by the superposition of two components with different temperatures • The main component, T = 4500 K - present in all spectra - temperature does not depend on velocity! - originates from a relaxed vapor cloud near and behind the meteoroid

    24. The second component, T = 10 000 K - present in bright and fast meteors (vapor lines – air lines present also in faint fast meteors) - temperature does not depend on velocity (or only slightly) - originates from a transition zone in the front of the vapor cloud - typical lines: Ca II, Mg II, Si II

    25. Two components Example of a Perseid fireball

    26. Determination of elemental abundances • Estimation of electron density • Use of Saha equation • Determine ionization degree • Recompute neutral atom abundances to total abundances

    27. Estimation of electron density • From meteor size and atom column densities + neutrality condition • From CaII/CaI ratio (if the high temperature component is absent) • By combining both components podivat se podrobneji !

    28. Electron density from atom densities

    29. Abundances in meteor vapors low cometary Fe/Mg volatile depletion in Geminids incomplete evaporation Cr ??

    30. Incomplete evaporation

    31. Abundances along the trajectory

    32. Ca/Fe model evaporation Schaefer & Fegley (2005)

    33. LOW RESOLUTION VIDEO SPECTRA OF METEORS

    34. Spectral and direct cameras in Ondřejov

    35. LEONID METEOR SPECTRUM November 18, 2001 10:24:14 UT Mt. Lemmon Meteor magnitude: –1.5

    36. frame 21P height 109 km IR end O [O] 557nm Na Mg blue end