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[Programme]
Session 4: "Optical Observations of
Meteors"
Date: Tuesday 16.00-17.25
Spectroscopic Study of Meteor and Persistent
Train
Shinsuke Avell Abe (1), Jun-ich Watanabe
(2), Hajime Yano (1) and Noboru Ebizuka (3)
1) The Institute of Space and Astronautical
Science; 2) National Astronomical Observatory; 3)
The Institute of Physical and Chemical Research
During the 1999 Leonid, an intensified HDTV
camera was used for slitless meteor spectroscopy at
visible and near-UV wavelengths in the Leonid
Multi-instrument Aircraft Campaign. The HDTV system
provided a high dynamic range (digital 10-bit) and
a wide field of view of 37 x 21 degrees. Here, we
report on the results for several particularly nice
spectrum from Leonid and Taurid meteors. Fe/Mg
abundance of Taurids is about 2 times higher than
that of Leonids. It is possible to build up a
hypotheses. A LTE temperature calculated by
numerous Fe emission lines below 550 nm is compared
with a electronic-vibrational temperature of N2 in
the visible (550 - 800 nm). It seems that meteor
spectra can be explained well by LTE model.
Moreover, stereoscopic observations of one
spectroscopic meteor have been accomplished during
the Leonid MAC and the real height of emissions
were measured. An excellent spectra of a Leonid
persistent train was obtained during the 1998
Leonid maximum in Japan by using a grating
spectrograph covering 370 - 640 nm wavelength
range. Identified Mg, Fe and Na suggests that these
atoms are the source of the persistent trains and
of long-lived emitters. 4.1
Differential Ablation of Meteoroids as
Observed by Ground-based Lidars
Ulf von Zahn and Josef Hoeffner
(Leibniz-Institute of Atmospheric Physics, 18225
Kuehlungsborn, Germany), Edmond Murad (Air Force
Research Laboratory, Hanscom AFB, MA 01731, U.S.A.)
and William J. McNeil (Radex Inc., Bedford, MA
01730, U.S.A.)
We report on an extensive set of new
observations of meteor trails by ground-based
lidars. The observations are performed with metal
resonance lidars which sound the atom densities of
Na, K, Fe, Ca, and Ca+ in the altitude range
between 80 and 105 km. At the Leibniz-Institute of
Atmospheric Physics we have clustered three such
lidars at one site for simultaneous common-volume
observations of meteor trails. We have also
enhanced our lidar observations of meteor trails
through co-located observations of meteors by an
image-intensified video camera.
The average rate of trail detections is 0.8
meteor trails per hour of lidar observations. The
total number of our lidar-observed meteor trails
stands at more than 1300. We show through
observations and modelling that the capability of
any lidar to detect meteor trails is strongly
altitude dependent. We estimate that Leonids must
have a brightness < +7 m (equivalent photometric
mass 0 micro g, diameter 0.35 mm) to become
detectable for our lidars.
The most important result of our research is the
discovery that lidar-observed meteoroids ablate
almost exclusively differentially. Differential
ablation shows up in the unexpectedly small number
of two- and three-element trails in comparison to
that of single-element trails (of 1279 analyzed
trails, only 42 trails are two-element trails and 6
are three-element trails) and the lidar-measured
ratios of metal abundances in meteor trails (all
averages of the various abundance ratios deviate
significantly from CI chondritic composition). The
preponderance of differential ablation for
meteoroids with masses in the milligram-to-gram
range could indicate that a very large percentage
of all meteoroids desintegrate into many tiny
particles in the early part of their atmospheric
entry. 4.2
The AKM Video Meteor Network
Sirko Molau (International Meteor
Organization)
The German Arbeitskreis Meteore (AKM) group has
been installing and operating a network of
automated image-intensified video cameras since
March 1999. It is based on the MetRec meteor
detection and analysis software, which allows for
efficient video observations with only a minimum of
human interaction. It is the first network of video
cameras ever that operates on a regular basis and
collects large amounts of meteor data in the
optical domain throughout the full year. As of
spring 2001, the network consists of ten stations.
Further stations in Germany and abroad are
preparing to join the effort, expanding the AKM
network into a global one. All data are compiled
into an archive that is freely accessible through
the Internet. The video meteor database contains
currently more than 24.000 single-station meteor
records from about 400 observing nights. The talk
will describe the development and current status of
the MetRec software including a short
demonstration. An overview over the present state
of the network will be given. We will describe the
structure of the database and illustrate its
application. Future plans like the automatic
analysis of multi-station video observations and
thorough meteor shower analyses will be addressed
in the outlook. 4.3
Results of Double-station TV Obsevations
during 1998 and 2000
Masayoshi Ueda (Nippon Meteor Society),
Yasunori Fujiwara, Masatoshi Sugimoto (Nippon
Meteor Society)
We carried out double-station TV meteor
observations during 1998 and 2000. The TV
observations could record faint meteors. The
radiant positions of Leonid and Taurid meteors was
determined. PSA-28
Double station TV Meteors and Analysis of
their Trajectories
R. Stork, P. Koten, J. Borovicka, P.
Spurny and J. Bocek (Astronomical Institute,
Academy of Sciences of the Czech Republic,
CZ&endash;25165, Ondrejov, Czech Republic)
The TV observation of meteors is performed in
Ondrejov since 1990. Together with taking meteor
spectra we started also double station observations
in the integral light in 1997. The stations are
located in Ondrejov and Kunzak, it gives the base
distance of 92.5 kilometers. We use camcorders with
image intensifier, the diameter of the field of
view is about 20 degrees, limiting magnitude about
8 for stars and 6&endash;7 for moving object
(meteor). Hundreds of shower and sporadic meteors
were recorded, about half of them are double
station ones. The selected meteors were measured on
digitized records from both stations and their
trajectories in the atmosphere and heliocentric
orbits were computed. Also K_B parameter
[Ceplecha Z. 1988, Bull. Astron. Inst.
Czechosl. 39, p. 221&endash;236] was computed
for meteors and the distribution of shower and
non-shower meteors into classes using that
criterion will be presented. 4.4
Meteor Head Echo Observations by the MU Radar
and Simultaneous ICCD Camera Observations
Takuji Nakamura (Radio Science Center for
Space and Atmosphere, Kyoto University) Toru Sato
and Koji Nishimura (Graduate School of Informatics,
Kyoto University)
The MU radar (middle and upper atmospheric
radar) is a VHF Doppler radar with a high output
power (46.5MHz, 1MW) with a large circular array
antenna (8330m^2). This radar has been used for
both atmospheric and meteoric studies by receiving
meteor tail echoes for over a decade. Recently, we
have applied the MU radar for measurement of meteor
head echoes and further developed two different
techniques for instantaneous measurement of meteor
orbits: the sequential beam lobing method and the
intereferometric method. The latter is found to be
more precise in orbit determination because of
rapid variation of radar cross section of head
echoes. Precision of this method is estimated to be
0.2 km/s and 0.5 degree for meteor speed and
velocity vector direction, respectively.
Simultaneous optical observation with an ICCD
(image intensified CCD) camera system (sensitive to
+9 mag. meteors) was carried out. From 229 minutes
observation, 1393 meteors were detected with the
radar and 34 meteors were simultaneously recorded
by the optical system. Comparative analysis
revealed that our radar observation is capable of
determining orbit of faint meteors up to +14.8
magnitude. Meteor velocity distribution and mass
estimation will also be reported in the paper.
4.5
Observation of Leonid Activity in 1998 and
1999 with the MU Radar and an All-sky TV
Camera
Takuji Nakamura, Sigeru Asakura and
Toshitaka Tsuda (Radio Atmospheric Science Center,
Kyoto University), Masayoshi Ueda (Nippon Meteor
Society) and Jun-ichi Watanabe (National Astronomy
Observatory)
The MU (middle and upper atmosphere) radar
observed a significant Leonid activity both in 1998
and 1999. A very strong activity with strong and
long lasting meteor echoes was observed between 21
UT on Nov. 16 and 02 UT on Nov. 17 (06-11 LT) in
1998. On the other hand, in 1999, a severe outburst
with strong but much shorter echoes was detected
just around the expected peak time of 2 UT on Nov.
18, 1999 (11 LT). In order to estimate the visual
magnitude and mass of the meteors during such
shower activity, we carried out an all-sky TV
observation with an image intensifier
simultaneously. By applying the ionized tail model
with attachment process of electrons, radar echo
durations are converted to meteor magnitudes. As a
result, we conclude that there were plenty of and
few fireballs (e.g., brighter meteors with
magnitude of -3 ) in 1998 and 1999. We further
discuss about the total mass of meteors during the
two outburst cases. PSA-29
ALIS (Auroral Large Imaging System) Used for
Optical Observations of the Meteor Impact
Process
Urban Brändström (1),
Björn Gustavsson (2), Åke Steen (3) and
Asta Pellinen-Wannberg (1)
1) Swedish Institute of Space Physics, Kiruna,
Sweden; 2) National Institute of Polar Research,
Tokyo, Japan; 3) RemSpace Group, Linköping,
Sweden
ALIS is a low-light imaging facility consisting
of six remote-controlled stations in northern
Sweden. The initial objective of the facility was
to study aurora from multiple directions and
reconstruct three dimensional distributions of the
phenomena with the tomographic inversion method.
The stations are located in a 50 km grid. They are
equipped with non-intensified, high-performance CCD
cameras, with telecentric lens systems and
filter-wheels with narrow-band (40 Å)
interference filters for auroral emission lines.
The field-of-view is 90°x90° at two
stations and 54°x54°at four stations.
Each camera is mounted in a positioning system,
enabling ALIS to monitor overlapping
fields-of-view. The facility can also be used for
real time meteor impact observations. Filters for
optically observable meteor constituents such as
sodium (5893 Å) and calcium (4227 Å)
can be used at two stations, while the others
measure the trail impact in white light. When a
meteor comes within the common volume its ablation
can be observed by making multiple exposures before
reading out an image. Exposure times down to 50 ms
and frame rates of one image per second are
possible. A simulation of how an ablation process
of sodium and calcium can be observed with this
facility is presented. PSA-30
Some Features of Digital Kinematic and
Photometrical Processing of Faint TV
Meteors
Pavlo M. Kozak, Alexander A. Rozhilo and
Yury G. Taranukha (Astronomical Observatory of Kyiv
Taras Shevchenko National University, Kyiv,
Ukraine
Some features of digital kinematic and
photometrical processing of TV faint meteors are
discussed. For these purpose a computer original
program has been worked out. The program uses data,
obtained by two TV devices, equipped by izokon TV
tubes. Observational images were recorded into
videotaperecorder and than digitized with the help
of a framegrabber. A precision of measurements of
meteor coordinates in the frame is estimated.
The kinematic processing is based on an original
method using in general elements of vector analysis
and calculates both meteor trajectory parameters in
Earth's atmosphere and orbit elements. The errors
of the parameters are also computed. Photometrical
characteristics of TV systems were investigated.
Some experiments for photometrical field
correction, spectral sensitivity of TV tube cathode
and correction for the motion of a meteor were
carried out. The method was approbated on the
results of basic observations of meteors for the
last years in Kyiv. PSA-31
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