[Prev][Next][Index][Thread]

(meteorobs) Excerpts From: CCNet DIGEST, 1 Oct 1998


[
 I particularly thought item (11) was of general interest, given some of
 our most recent discussions about meteoroid sizes, dispersal patterns,
 etc. Enjoy! -Lew Gramer
]

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST 01/10/98
Date: Thu, 1 Oct 1998 10:39:58 -0400 (EDT)


CCNet DIGEST, 1 October 1998
----------------------------------------------
...
(3) METEORITE PICTURE?
      Paolo Farinella <paolof@keplero.dm.unipidot it> 
...
(9) THE DEATH OF COMET TABUR 1996 Q1
      M. Fulle et al., ASTRONOMICAL OBSERVATORY TRIESTE
...
(11) DYNAMICS OF COSMIC DUST NEAR THE SUN
        A. Krivov et al., MAX PLANCK INSTITUTE
...

=====================
(3) METEORITE PICTURE?

>From Paolo Farinella <paolof@keplero.dm.unipidot it> 
 
I have recently visited the Melk Monastery, not far from Vienna, which has been 
completely restored some a few years ago and is now a magnificent (mainly early 
XVIII century) complex of buildings, overtowering the village and the Danube. 
In the small museum inside the Monastery there are several XV century
paintings, including one on the martyrdom of St. Catherine by a painter
called Hans Egkel.
Now, the painting shows a strange scene, with a kind of dark opening in the
sky from which angels throw many stones toward the ground, aiming (I suppose)
at the  evil characters who are putting the Saint to death. Now, the museum
catalogue gives `um 1470' for the painting's date, but I don't know which
uncertainty does `um' imply. Might it be possible that the painting was done
after the 1492 Ensisheim fall, given the wide circulation of the news about
it in central Europe (see the beautiful article by Marvin 1992, "Meteoritics"
27, 28-72)? Or that is there some other connection to real meteorite falls?
Please send me any information or suggestion on this matter at:
        paolof@dm.unipidot it
 
                                   Paolo Farinella

==================================== 
(9) THE DEATH OF COMET TABUR 1996 Q1

M. Fulle*), H. Mikuz, M. Nonino, S. Bosio: The death of comet tabur 1996 Q1: 
The
tail without the comet. ICARUS, 1998, Vol.134, No.2, pp.235-248

*) ASTRONOMICAL OBSERVATORY TRIESTE, VIA TIEPOLO 11, I-34131 TRIESTE, ITALY

After a normal brightness increase, Comet Tabur 1996 Q1 showed a remarkable 
photometric behavior by rapidly fading in late October 1996. In this paper we 
analyze three CCD images of the remnant dust tail observed during the fading
of the  comet around perihelion and model them by means of the inverse dust
tail model (M. Fulle, 1989, Astron. Astrophys. 217, 283-297). Assuming
hemispherical sunward dust emission from the nucleus, satisfactory fits of
the observed tail brightness distribution, turning axis and temporal fading
allow us to conclude that only dust was observed, and contamination by gas
and/or ions in the images is negligible. The model results include the
temporal variation of the dust ejection velocity, the size distribution and
dust mass loss rate. These values show a strong correlation during fading
with strong drops consistent with the comet's deactivation. In particular,
the slow increase of the dust mass loss rate in September and its low
absolute values allow us to exclude outbursts preceding fading and to exclude
that the disappearance was due to a complete nucleus disruption. In this case,
the nucleus mean radius should have been no more than 350 m (for a nucleus
bulk density of 100 kg m(-3)), which seems inconsistent with the observed
water loss rate. A probable explanation of the comet fading is that the
comet nucleus deactivation was due either to seasonal effects, putting all
active areas in permanently night sides, or to the complete end of the whole
nucleus surface activity (possibly due either to nucleus mantling or to the
end of the ice reservoirs). (C) 1998 Academic Press.

==========================================
(11) DYNAMICS OF COSMIC DUST NEAR THE SUN

A. Krivov*), H. Kimura, I. Mann: Dynamics of dust near the sun. ICARUS, 1998, 
Vol.134, No.2, pp.311-327

*) MAX PLANCK INST AERON,KATLENBURG DUHM,GERMANY

In an effort to shed some light on the main features of the innermost part of 
the zodiacal cloud, the solar F-corona region, for which both observational and
theoretical studies still give controversial results, we model the dynamics and 
physical evolution of dust grains at several solar radii (Ro) from the Sun. We 
take into account solar gravity, direct solar radiation pressure, Poynting-
Robertson force, sublimation, and the Lorentz force. The latter is computed
on the base of: (i) the grain surface potentials derived from elaborate model
calculations and shown to vary from +3 to +12 V; (ii) a multipole radial model
of the actual solar magnetic field for the period 1976-1996. The dust particles
are assumed to be porous and compact spherical grains, made of two types of
material: dielectric (silicate) grains and absorbing (carbon) ones. Our main
results can be summarized as follows. The decrease of grains' sizes and the
dynamics of particles in the orbital plane are well described by taking into
account solar gravity and radiative forces together with the sublimation
process, being relatively insensitive to the electromagnetic force. The
silicate grains typically move inward in near-circular spirals until intensive
sublimation starts and they disappear at heliocentric distances from 2 to 3 R.
The carbon grains intensively sublimate near 4R. After several radial
oscillations, they are eventually ejected out as beta-meteoroids, when they
approach a critical radius of approximate to 2.4 mu m (for porous grains) or
approximate to 0.5 mu m (for solid spheres), which corresponds to the radiation
pressure to solar gravity ratio beta equal to unity. The orientation of the
orbital planes of the particles is dictated by the Lorentz force. Both porous
and compact carbon grains possess high beta ratios and must be larger than
respectively 2.4 and 0.5 mu m to reach the near-solar region. For these sizes,
the Lorentz force is relatively weak, comes basically from the dipole zonal
component of the field, and leads to low-amplitude oscillations of orbital
inclinations and a precession of the lines of nodes. The same behavior is
predicted for silicate porous (compact) grains larger than 2 mu m (1 mu m)
and 1 mu m (0.5 mu m) for the periods of quiet and active Sun, respectively.
From these sizes to smaller ones, the Lorentz force effectively broadens the
initial distribution of inclinations of silicate grains.

Submicrometer-sized particles easily get in polar and retrograde orbits well 
before the evaporation. On the whole, we find that the dynamics of near-solar
grains depend radically on their sizes, chemical composition, and structure
and, in cases of relatively small dielectric grains, may be severely correlated
to the solar activity cycle. (C) 1998 Academic Press.

----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe, please 
contact the moderator Benny J Peiser at <b.j.peiser@livjm.acdot uk>. 
Information circulated on this network is for scholarly and educational 
use only. The attached information may not be copied or reproduced for 
any other purposes without prior permission of the copyright holders. 
The electronic archive of the CCNet can be found at 
http://abob.libs.ugadot edu/bobk/cccmenu.html

------- End of Forwarded Message