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(meteorobs) Excerpts from "CCNet DIGEST 16 Oct 98"


On interesting item this week, from our own Jiri Borovicka!

Enjoy,
Lew

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST 16/10/98
Date: Fri, 16 Oct 1998 13:45:37 -0400 (EDT)

CCNet DIGEST, 16 October 1998
-----------------------------

[Please note that I will be abroad until 27 October 1998]

...
(3) BOLIDES PRODUCED BY IMPACTS OF LARGE METEOROIDS INTO THE EARTH'S
    ATMOSPHERE
    Jiri Borovicka <borovic@sunkl.asudot cas.cz>
...

------------------------------------------------------
(3) BOLIDES PRODUCED BY IMPACTS OF LARGE METEOROIDS INTO
    THE EARTH'S ATMOSPHERE

>From Jiri Borovicka <borovic@sunkl.asudot cas.cz>

Dear Dr. Peiser,

I enclose the abstract of a published paper which could be of interest
to the subscribers of the Cambridge-Conference.

Sincerely,

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

Bolides produced by impacts of large meteoroids into the Earth's
atmosphere: comparison of theory with observations
II. Benesov bolide spectra

J. Borovicka(1), O.P. Popova(2), A.P. Golub'(2), I.B. Kosarev(2)
and I.V. Nemtchinov(2)

(1) Ondejov Observatory, Astronomical Institute of the Academy of
Sciences, CZ-251 65 Ondejov, Czech Republic
(2) Institute for Dynamics of Geospheres, Russian Academy of Sciences,
Leninsky pr. 38, build. 6, 117979 Moscow, Russia

Received 24 February 1998 / Accepted 3 June 1998

Abstract

The unique observational spectrum of the very bright Benesov bolide EN
070591 is compared to theoretical bolide spectra. The -19.5 mag bolide
was induced by a meteoroid of an estimated initial mass of 4000 kg, a
density of 2 g cm-3 and a kinetic energy of 10^12 J (0.2 kT TNT). The
ablating piston model predicts spectra of large bolides by radiative
hydrodynamics calculations. We present examples of the calculated
H-chondrite vapor spectral opacities and of the resulting spectra for
various parameters.

Both theoretical and observed spectra show that bolide radiation is
composed of atomic line emissions, molecular bands and continuum
radiation. The role of the continuum increases with increasing
meteoroid size and with decreasing altitude. The atomic lines are
produced under the effective excitation temperature of 4000-6000 K.

The lines of Fe I are too faint and the lines of Ca I are too bright in
the model in comparison with the observations. Also the computed
continuum level is too high. These differences can be explained by
the fact that the vapors occupy a larger volume and have lower density
than predicted. This is probably a consequence of a mutual interaction
of fragments after the meteoroid fragmentation and of a not well
understood ablation process. Other differences between the theory and
the observation are described and possible model improvements are
discussed.

Key words: meteoroids, meteors

Send offprint requests to: J. Borovicka (borovic@asudot cas.cz)

(c) European Southern Observatory (ESO) 1998

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