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 Jiří Borovička Department of Interplanetary Matter
All-sky image Kouřim bolide (– 13 mag)
Meteor speeds 11 – 73 km/s Faint meteors: 110 – 80 km Fireballs: 200 – 20 km Meteor heights
Battery of six photographic grating cameras with rotating shutter in Ondřejov
Example of photographic grating spectrum of a slow sporadic fireball zero order first order second order
Detail of a Perseid spectrum almost head-on meteor blue part shown (3700–4600 Å)
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)
Free parameters • Excitation temperature, T • Column densities of observable atoms, Nj • Meteor cross-section, P • Damping constant,
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
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
Two components Example of a Perseid fireball
Determination of elemental abundances • Estimation of electron density • Use of Saha equation • Determine ionization degree • Recompute neutral atom abundances to total abundances
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 !
Abundances in meteor vapors low cometary Fe/Mg volatile depletion in Geminids incomplete evaporation Cr ??
Ca/Fe model evaporation Schaefer & Fegley (2005)
LEONID METEOR SPECTRUM November 18, 2001 10:24:14 UT Mt. Lemmon Meteor magnitude: –1.5
frame 21P height 109 km IR end O [O] 557nm Na Mg blue end