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[Programme]
Session 1: "Dynamics and Manifestation
of Meteor Streams"
Date: Monday, 8.45-12.30
Visual and Radar Observations of the Perseid
Meteor Stream 1953-83
B.A. Lindblad (Lund Observatory, Box 43, SE-221
00 Lund, Sweden)
This paper describes a long term,
high-resolution study of the activity of the
Perseid meteor stream based on visual and radar
observations at the Onsala Space Observatory in
Sweden. The data sample consists of 147 visual
hourly rates and some 2000 radar hourly rates
recorded in mid-August in the period 1953-83. In a
previous paper (Lindblad 2000) a high-resolution
study of the visual zenithal hourly rates of bright
Perseid meteors versus solar longitude was
described. The study using a step length of
0.05° in solar longitude, revealed that the
Perseid activity curve has a multi-peak structure
with at least four separate and well-defined peaks
in the activity curve of bright Perseid meteors. In
the present paper we analyse more than 2000 radar
hourly rates obtained during the same period. Each
hourly rate is available in three different echo
duration classes. It is well known that the
percentage of Perseid meteors is highest amongst
the echoes of long duration. We therefore here
analyse hourly rate counts of echoes of duration
1.0 sec and longer, corresponding approximately to
visual magnitudes of 2.5m and brighter. The
activity curve of the Perseid stream based on these
bright meteors is studied. The radar data very
strongly support the previous visual data
indicating several separate and permanent peaks of
stream activity. 1.1
Millimeter Continuum Observations of Parent
Comets of Meteor Storms
Hitoshi Hasegawa (ASTEC, Inc.), Nobuharu
Ukita (Nobeyama Radio Observatory) and Ryosuke
Nakamura (NASDA)
The 2 millimeter continuum observations of
parent comets of meter storms, P/Tempel-Tuttle and
P/Giacobini-Zinner, were made with a bolometer
array installed on the 45m radio telescope at the
Nobeyama Radio Observatory. P/Tempel-Tuttle was
observed on January 16 1998, near its closest
approach to the earth, and P/Giacobini-Zinner was
observed November 5 and 8 1998. The maps obtained
showed no signal from these comets greater than
12.0 mJy for P/Tempel-Tuttle and 17.4 mJy for
P/Giacobini-Zinner (3 sigma). Using the same
assumptions in Jewitt and Mathews (1997, AJ, 113,
1145), we estimated that the mass upper limits in
the 12 arcsec beam were 7.5E9 kg and 6.2E10 kg for
P/Tempel-Tuttle and P/Giacobini-Zinner
respectively. We esitimated total mass of these
meteor streams form the observed upper limits. The
derived total mass upper limits are serveral orders
larger than those expected from meteor
observations. 1.2
The IAU Meteor Data Center
B.A. Lindblad (Lund Observatory, Lund,
Sweden)
The IAU Meteor Data Center (MDC) in Lund acts as
a central depository for meteor orbits obtained by
photographic, video and radar techniques. It was
started in 1978 at the suggestion of the present
author. The photographic data sample now consists
of 4580 precisely reduced orbits plus 2401
graphically reduced orbits. The reformatting of the
precisely reduced orbits to a standard format has
been a major undertaking since each author/station
has used a somewhat different format. There is also
some overlap between the various catalogues. For
details see the IAUMDC Documentation pamphlet.
As of 1 Jan. 2002 the responsibility of
operating the MDC will be transferred to the
Astronomical Institute of the Slovak Academy of
Sciences in Bratislava, Slovakia with Dr. V.
Porubcan as the responsible scientist.
Dr. V. Porubcan and co-workers have been
involved in various studies of the photographic
data-base. They are preparing a new version which
is based on the year 2000 equinox (instead of the
1950 equinox used in nearly all of the published
catalogues). They have also made extensive studies
of the errors in some of the older photographic
data. A description of this work is presented in
Lindblad, Neslusan, Svoren and Porubcan (2001).
PSA-1
Parent Objects of Alpha Capricornid Meteor
Stream
Ichiro Hasegawa
The complex structures of Alpha Capricornid
stream are investigated from about 45 photographic
meteors observed during July 8 and September 10.
Although there are several subgroups in this
stream, it is confirmed that the main parent comet
is 45P/Honda-Mrkos-Pajdusakova.
72P/Denning-Fujikawa and 141P/Machholz 2 are likely
to be additional parent comets. Near earth objects,
(2101)Adonis and (9162)1987 OA are also suggested
as the possible parent objects. 1.9
Asteroid (1620) Geographos as a Possible
Parent Body for a Meteor Stream
G.O. Ryabova (Research Institute of Applied
Mathematics and Mechanics, Tomsk, 634050, Russia.
E-mail: astrodep@niipmm.tsu.ru)
The study was undertaken to answer the following
questions: when and how particles could escape from
the asteroid, could they reach the Earth and could
we detect some of them in available meteoroid orbit
databases. It was found that the rotational
acceleration does not exceeds the gravitational one
for all possible rotational states. So the escape
of particles from the asteroid apparently took
place during a close approach with the Earth (plus
tidal forces) or in a collision. Numerous model
streams having different schemes and times of
ejection were considered. It was obtained that
model meteoroid streams ejected with high
velocities (up to 1 km/s) can approach the Earth's
orbit twice, once before (February-March) and once
after (August) perihelion. There were found 44
correlated meteor orbits (in databases containing
> 75000 orbits) from the both showers and a
taxon structure was derived for them. The
distribution of ejection velocity vectors looks
like originated at impact of a catching up small
body, but the time of the collision remains
unknown. So, with the high probability Geographos
is the parent body for a meteor stream, generating
twin meteor showers observable at the Earth :
Spring and Summer Geographides. 1.10
Mathematical Model of the Geminid Meteor
Stream Formation
G.O. Ryabova (Research Institute of Applied
Mathematics and Mechanics, Tomsk, 634050, Russia.
E-mail: astrodep@niipmm.tsu.ru)
The Geminid meteoroid stream formation and
evolution was studied by the method of nested
polynomials. Besides other results the present work
puts forward a new theory to explain the secondary
maximum of the Geminid rate profile: branches of
the stream have been formed due to differences in
orbital parameters of particles ejected from the
cometary nucleus before and after perihelion. The
model stream originated in such a way has a
distinguishing feature: the smaller meteoroid mass,
the greater the distance between maxima. Their
relative positions depend on the stream age. If the
stream is young then as meteoroid mass increases
the every next pair of maxima appears to be
enclosed in the previous one. (Like a Russian doll
"matrioshka"). Such is indeed the case of the
Geminids. So we have a weighty argument in favour
of the cometary past of the asteroid Phaethon (the
parent body). A comparison of the model and
observed rate profiles allowed to propose a
hypothetical scenario of the comet disintegration:
greater intensity of dust production before
perihelion, significant change of the cometary
orbit due to jet forces and ejection of dust in the
wide cone directed to the Sun. PSA-2
The 2000 Ursid Shower Prediction and
Observations
P. Jenniskens (SETI Institute, at NASA Ames
Research Center) and E. Lyytinen (Finland)
We applied Leonid dynamical models to
Halley-type comet 8P/Tuttle and its meteor shower,
the Ursids. An outburst was predicted for December
22, 2000, when Earth was to cross the dust trails
that originated during the 1392 and 1405 returns.
An announcement was made in the IAU circulars and
in extended form in WGN, the Journal of IMO. The
meteor outburst observed from California using
video and photographic techniques. At the same
time, five Global-MS-Net stations in Finland, Japan
and Belgium counted meteors using forward meteor
scatter. We can now confirm the return of the Ursid
outburst with a maximum at 8:06±07 UT,
December 22nd, when activity peaked at ZHR ~ 90.
The Ursid rates were above half peak intensity
during 4.2 hours. The relative contribution from
both dust trails to the outburst is discussed, as
is the relevancy of this for future meteor outburst
forecasts. PSA-3
Combined Visual and Radar Observations. 45
Years Later
O.I. Belkovich (Zelenodolsk Branch of the
Kazan State University, Russia) and V.S.
Tokhtas'jev (Engelhardt Astronomical Observatory,
Russia)
Combined visual and radar observations of
Perseids made by B.A. Lindblad at the Onsala Wave
Propagation Observatory, Sweden between 1953 and
1961 have been processed taking into account random
positions of reflecting points on meteor trails and
the modern physical theory. As a result the new
more accurate relation of ionization and luminosity
coefficients has been found for Perseids meteors.
Velocity dependence of this relation was found from
the analysis of other data. PSA-4
Comparative Analysis of Meteor Shower
Observations Processed by Three Different
Methods
O.I. Belkovich (1), M.G. Ishmukhametova
(2), N.I. Suleimanov (3) and V.S. Tokhtas'jev
(3).
(1) Zelenodolsk Branch of the Kazan State
University, Russia, (2) Kazan State University,
Russia, (3) Engelhardt Astronomical Observatory,
Russia
Long-term series of radar and visual
observations of Geminids and Quadrantids have been
used for the analyses. Processing of radar
observations has been made by the two methods: 1)
the flux density has been calculated from hourly
number of meteors with amplitudes exceeding the
radar threshold level, 2) from hourly number of
reflections from overdense meteor trails with
durations greater than 1 second. The S coefficient
of meteoroid mass distribution as a function of the
solar longitude has been found from rations of two
flux densities. Reduced zenith hourly rates for
meteors brighter than +3 magnitude from visual
observations of the showers have been found by the
method worked out at the Engelhardt Observatory.
Profiles of the showers (flux densities or ZHR as
functions of the solar longitudes) depends on the
minimal registered masses of meteoroids. This fact
has given us the opportunity to check as the
correctness of the methods of processing of
observations so to do independent estimation some
parameters of the physical theory of meteors (mass
scales of radio and visual meteors). The estimation
of the collecting area in visual observations of
meteors has been made also. PSA-5
Temporal Structure of Meteoroid Stream and
Lunar Seismicity According to Nakamura's
Katalog
O.B. Khavroshkin and V.V. Tsyplakov
(Schmidt United Institute of Physics of the Earth,
Russian Academy of Sciences, B.Gruzinskaya 10,
123885 Moscow D242, Russia)
Nakamura and Oberst pioneered in receiving data
of clustering of meteoroid streams from impact
seismograms. As a continuation of their research we
have derived some types of temporal series. Two
series 1 and 7 years in persistence (1974 and
1969-1977) are the temporal sequences of sum
numbers of impacts per unit time (one day, three
days). The third series one year in persistence
(1974) is the temporal sequence of impact events
and time intervals between them according to
Catalogue. We adopted that event amplitudes are
equal to unit. The duration of these events was
obtained from impact seismograms. The forth series
with the same persistence (1974) is the temporal
sequence of values equal to duration of impacts
averaged through day. All series were studied by
spectral analysis and as a result, common
periodicity for all series and supplementary picks
in only two series were obtained. Spectrum of the
series (1969-1977) disclosed time picks on Mercury,
Venus and Earth orbital periodicity (88; 115; 225;
365, 27.3 days). Comparative analysis of spectra
for other series disclosed following periodicity
picks: 44; 27; 5,5; 3,7 (for first series 1974 in
persistence); 10; 5; 3; 2.5; 2.23 days (for third
series); 10; 5; 3,3; 2.5; 2,23 days (for forth
series). The 10 and 5-days picks are exceptionally
interesting, because magnetic solar storms have the
same periodicity. The dust component of meteoroid
streams similar to dust plasma probably is
modulated by variation of solar magnetic fields.
Thin temporal structure of temporal variation of
meteoroid streams has the picks which coincide with
half-periods of neighbourhood binary star systems (
2.2 day - UWCma; 3.6 days - hAql). PSA-6
Meteoroid Stream Impacts on the Moon:
Information of Duration of Seismograms
O.B. Khavroshkin and V.V. Tsyplakov
(Schmidt United Institute of Physics of the Earth,
Russian Academy of Sciences, B.Gruzinskaya 10,
123885 Moscow D242, Russia)
The seismograms of meteoroid stream impacts on
the Moon have brought important information about
inside structure of the Moon more years ago. This
work is a new attempt of using records of "Apollo"
seismic network for receiving further information
about dynamic processes on the Moon. The Nakamura
Catalogue is employed for research of these
problems. We have built up some histograms from
seismic data of Catalogue. The duration of impact
_imp in minutes was a general parameter for our
analysis. The impact duration was plotted on the
horizontal axe of histogram and sum number of
impacts _ni for every impact duration was plotted
on its vertical axe. In other words, these
histograms are the graphic images of relationships
between _ni and _imp. Following kinds of
functions_ni=_ni(_imp) are analysed: (1)- one
impact of a meteoroid per Earth day; (2) - two
impacts per day; (3) - three impacts per day; (4) -
(four-eight) impacts per day; functions (1)-(3)
have been built up only within 1974 year; function
(4) have been built up for every year within
1974-1977 and for their sum also. Preliminary
conclusions of processing histograms is as follows:
the increase of energy of impact from (1) to (3)
moves a maximum of histograms to shorter duration,
especially it is evident in the case of 4-8 impacts
per day; every histogram contains significant picks
which are 58-56; 40; 38; 25; 19-20; 16 minutes, but
6; 10,13 minute picks are existed only for 4-8
imp/day histogram. We expect that physical models
for explaining these picks might be discuses in the
meeting. 1.3
A Fine Structure of Perseid Meteoroid Stream.
Method of Indices
J. Svoren (1), V. Porubcan (2) and L.
Neslusan (1)
(1) Astronomical Institute of the Slovak Academy
of Sciences, SK-059 60 Tatranska Lomnica, The
Slovak Republic, (2) Astronomical Institute of the
Slovak Academy of Sciences, Dubravska 9, SK-842 28
Bratislava, The Slovak Republic
A procedure based only on mathematical
statistics is used to study the fine structure of
the Perseid stream and its filaments which cannot
be reliably separated by iteration methods. Besides
the five orbital elements incorporated in the
Southworth-Hawkins D-criterion, we also take into
account the coordinates of the radiant which belong
to the most precisely determined parameters and the
geocentric velocity as a significant parameter
characteristic for physically related orbits. The
basic idea of the procedure is a division of the
observed ranges of parameters into a number of
equidistant intervals and assignment of indices to
a meteor according to the intervals pertinent to
its parameters. The meteors with equal indices are
considered for mutually related. Since various
parameters listed in the catalogue contain various
relative errors, it is necessary to use different
numbers of intervals in the division of each
parameter to obtain a good fit with the real
orbital distribution. The relative ratios,
approximated by small integers, corresponding to
the reciprocal values of the relative errors of
parameters, are applied as the basic numbers for
the division of the parameters. Our results are
compared with the known filaments of the Perseid
meteoroid stream discovered by other authors.
PSA-7
The Discrete Solution of a Quasi-thomography
Problem for Construction of the Radiant
Distribution of Meteors by Results of Radar
Goniometer Measurements
Vladimir Sidorov and Sergey Kalabanov
A new solution of the quasi-tomographic
determination of the spatial distribution of the
meteoric complex as constructed from radar
goniometer data is represented for the first time.
A previous solution obtained by O. Belkovich,
V.Sidorov and T. Filimonova was based on the
assumption of a continuous radiant distribution of
sporadic meteors on the celestial sphere. In that
theory, the number of unknowns grew quadratically
with increase of the angular measurement accuracy.
Therefore a stable solution was possible only for
the angular measurement accuracy in 10 x 10 deg
bins. The new solution is obtained using the
hypothesis that there is a discretization in the
angular radiant distribution of meteors. It assumes
the meteor flux consists, not of an ensemble single
meteors, but consists of a system of showers and
microshowers with close velocities and close
angular grouping. The new method uses a computer
optimization of such a radiant distribution on the
celestial sphere subject to constraints of the
microshower hypothesis, the mirror condition of
trail reflection and other independent
measurements. The method is implemented on a
computer for routine goniometer processing with
discrete2 x 2 deg bins and has been used for
determination of meteor shower orbit parameters on
one day of radar observation, December 13 1986.
1.4
Thin Space Structure of Meteor Flux
Irregularities in Large Meteor Showers in 1986
-1999
A.V. Karpov and E.Z. Yumagulov
Meteoric observations obtained with the radar
KGU-M5 (1986 - 2000), have been archived in an
Oracle 8 relational database. An advanced
statistical method of searching for fine spatial
structure of meteoric showers has been applied to
the database and information on the distribution of
material in the Quadrantid, Geminid and Perseid
showers has been obtained.
For the Geminid meteor shower, evidence of
grouping was found in 49 % of the intervals of
observation (similarly for the Quadrantid and
Perseid showers 39% and 63 % were obtained,
respectively.). The results also had a dependence
on signal level. Groupings were detected (a) in 79
% of cases only at low signal level, (b) in 17 % of
cases the groupings were detected at both high and
low levels detection, and (c) in 4 % of cases
groupings were found only at high signal levels and
they were absent at low levels. The prevalence of
groupings observed at low signal levels corresponds
qualitatively well to that of a Poisson model of
particle distribution. 1.5
The Determination of the Ejection Velocity of
Meteoroids
I.P. Williams (Faculty of Engineering and
Mathematical Sciences, Queen Mary, University of
London; E-mail I.P.Williams@qmw.ac.uk)
A knowledge of the ejection velocity of
meteoroids from the nucleus of a parent comet is
important both for an understanding of processes
ongoing in cometary nuclei and the accurate
modelling of the evolution of the resulting stream.
However, determination of this from the
observations of comets tends to be difficult, since
observational techniques focus on grains of sizes
that are different from meteoroids. Similarly,
determination from the study of meteor showers is
also difficult because the properties of the
observed meteor shower are generally affected by
post-ejection evolution through the effects of
radiation and planetary perturbations. Thus in
order to make deductions regarding the meteoroid
ejection velocity from the study of meteor showers,
we must a) find a shower that is so young that
evolutionary effects are ignorable or b) find a
stream where evolution is unimportant or c) we must
find a shower that has some special characteristic
whose appearance is very sensitive to the ejection
velocity. The aim of this talk is to discuss these
three options and compare the results so obtained.
1.6
A New Meteor Shower, eta Eridanids
Katsuhito Ohtsuka (Tokyo Meteor Network) and
Tomoyasu Tanigawa (Nishinomiya-Nishi High
School)
From among approximately 1000 optical meteor
data obtained during the past few decades, we
discovered a total of 5 (4 probable and 1 possible)
meteors which belong to a new meteor shower, eta
Eridanids. Several visual and radar observations
reinforces the evidence that the eta Eridanids
surely exist. We also found out Comet D/1827M1
(Pons-Gambart) and Comet C/1852K1 (Chacornac) as
the parent comet candidates. However, the eta
Eridanids are rather associated with Comet
Chacornac than Comet Pons-Gambart, judging from
their orbital similarities. PSA-8
Resonance Structure of Meteoroid Streams
V.V. Emel'yanenko (South Ural University,
Russia)
The dynamical behaviour of meteoroid streams is
studied on the basis of the resonance theory of
perturbations. Parameters are calculated for the
principal resonance zones near the orbits of the
main meteoroid streams. The features of changes in
the spatial number density for librating,
circulating and stochastic-type motion are
described. In the case of librations near centres
of resonances, the density of meteoroid streams
changes almost periodically, and resonant particles
produce compact trails. On the other hand, the
stochastic motion of meteoroid streams is similar
to that of a diffusion process. The Leonid, Lyrid,
Ursid, Perseid and Bootid outbursts as indicators
of the described dynamical features are discussed.
Recommendations are given for the future
observations of the annual meteor showers. 1.7
Comparison among the
Keplerian-orbit-diversity Criteria in
Major-meteor-shower Separation
L. Neslusan and P.G. Welch
Recently, two new criteria of diversity of
Keplerian orbits have been suggested, that by
Valsecchi, Jopek, and Froeschle (VJF) in 1999, and
orbital-momentum-based (OMB) criterion by Neslusan
in 2001. In the presented paper, there is a
comparison of how the classic, Southworth-Hawkins
(SH) criterion from 1963, and both new criteria
behave, when these are used in the separation of
several major meteor showers from the photographic
IAU MDC database. The
cumulative-number-on-threshold-D-dependence method,
based on work by Sekanina from the beginning of
seventies, is utilized to perform an optimal
separation. The quality of separation is evaluated
with the help of "background-number-density test"
(described here in more detail). No general
difference among the particular criteria was found.
A relatively worse result is obtained using SH
criterion for Perseids. The separation method does
not work with the VJF and OMB criteria for the
alpha-Capricornids, and with OMB criterion for the
Northern as well as Southern delta-Aquarids.
PSA-9
Extreme Beginning Heights for Non-Leonid
Meteors
Pavel Koten, Pavel Spurny, Jiri Borovicka
and Rostislav Stork (Astronomical Institute,
Academy of Science, Ondrejov Observatory, 251 65
Ondrejov, Czech Republic)
Extreme beginning heights up to 200 km were
recently discovered for bright Leonid meteors. Here
we report results of the search among our
double-station video data of other meteor showers.
We found two eta-Aquarid and one Perseid meteors
with beginning heights up to 150 km and one Lyrid
meteor with beginning height above 130 km.
Surprisingly, the eta-Aquarids and the Lyrid were
not bright enough to be recorded by all-sky
photographic cameras. PSA-10
TV Observation of the 1998 Giacobinid Meteor
Shower in Japan
Y. Fujiwara, M. Ueda, M. Sugimoto and T.
Sagayama (Nippon Meteor Society), M. Satake and A.
Furoue (Kansai Astronomical Society)
Activity of Giacobinid (Draconid) meteor shower
was recognized on October 8th, 1998, in Japan, with
multi-station TV observations. 104 Giacobinid
meteors have been recorded, and among which precise
orbit could be determined for 60 meteors. It is
found that the radiant points were concentrated
compactly. Furthermore, the beginning heights of
Giacobinid meteors are significantly higher than
typical TV meteors with similar velocities.
PSA-11
Constraining Cometary Ejection Models from
Meteor Storm Observations
Michael Mueller, Simon F. Green and Neil
McBride (Planetary and Space Science Research
Institute, Open University, Walton Hall, Milton
Keynes, MK7 6AA, UK)
Modelling and observations of the Leonid
activity in recent years have shown that maxima in
the meteor storm activity can be identified to be
due to particles released from the comet during a
certain perihelion passage. If the particles
originating from a certain perihelion passage can
be identified, it is an obvious next question to
ask what information can be gained about the
ejection process of particles from a cometary
nucleus. To address this question we have developed
a model which allows calculation of the particle
number density in a dust trail physically
consistent for arbitrary complex activity
distributions of a comet with numerical integration
of only relatively few trajectories. The model is
applied to the Leonid activity in the year 2000. It
is shown that particles of different sizes entering
the Earth atmosphere at the same time were released
from the comet at different heliocentric distances.
Therefore one has to make assumptions about the
activity of the comet with heliocentric distance in
order to derive the cometary size distribution from
an observed meteor size distribution. However, it
is shown that lower limits on the ejection velocity
of the observed particles can readily be derived.
1.8
The Updated Version of the IAU MDC Database
of Photographic Meteor Orbits
B. Lindblad (1), L. Neslusan (2), J. Svoren (2)
and V. Porubcan (3)
(1) Lund Observatory, 22100 Lund, Sweden, (2)
Astronomical Institute, Slovak Academy of Sciences,
05960 Tatranska Lomnica, Slovakia, (3) Astronomical
Institute, Slovak Academy of Sciences, 84228
Bratislava, Slovakia
The database of photographic meteor orbits of
the IAU Meteor Data Center in Lund has gradually
been updated. The version 2001, which has been
prepared for publication and which will be released
soon, contains complete orbital and geophysical
data on 4581 meteors. Several catalogues have been
published in some stations and thus a given
publication serial number may correspond to several
meteors. To remove ambiguity, we now introduce a
new meteor identification code consisting of the
publication serial number, the author or station
code, and the number of the catalogue. The database
contains geophysical parameters and orbital
elements, which are mutually dependent. Therefore
one set can be used to verify the correctness of
the other. This verification and appropriate
corrections are done. The distribution of database
is again planned as two separate files: one with
orbital, another with geophysical data. A file
containing all data merged and orbits homogenized
will be available, too. All the files as well as
the appropriate documentation will be placed on a
WWW-site to enable their free, public downloading.
PSA-12
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