ACM'99 : Leonids'98
Scientific Program Abstracts
Session 7: Leonids: Up Close and Personal
Tuesday, July 27 10:50-12:30
P. Jenniskens and I.P. Williams, moderators
Results from the Leonid Multi-Instrument Aircraft Campaign
P. Jenniskens (SETI Institute/NASA Ames Research Center)
In November of 1998, 28 scientists of seven nationalities participated in NASA's first Astrobiology mission, an airborne campaign to study the accretion of extraterrestrial materials in Earth's atmosphere during the unusual Leonid meteor shower from a location near Okinawa, Japan. This Leonid Multi-Instrument Aircraft Campaign offered excellent observing conditions at the best place for viewing and helped deploy a wide range of imaging, spectroscopic and ranging techniques to study the meteor shower. The NSF/NCAR "Electra" aircraft carried a two-beam iron lidar of the University of Illinois amongst five other experiments. The USAF/452nd FTS "FISTA" aircraft carried mid- and near-infrared spectrographs of the Aerospace Corporation and the Air Force Research Laboratory, in addition to seven other experiments. There were no unsolved technical problems and the mission proceeded as planned. What is arguably the best shower since the storm of 1966 was observed in close detail. In addition, some of the ground-based efforts in China and the USA set up by some of the participating researchers were highly successful also by profiting from local clear weather conditions. Here, I will introduce the mission objectives and scope and will discuss some of the first results of the various research teams presented during the Leonid MAC Workshop at NASA/ARC in April of 1999. This workshop was the first step in our preparations for a second such campaign in November of 1999, this time to be flown from a site in Europe.
The Age, Structure and development of the Leonid Meteoroid Stream
P. Brown, J. Jones (Department of Physics and Astronomy, University of Western Ontario)
We present and develop a numerical model of the Leonid stream. From the results, we have demonstrated that the strongest returns from the Leonids are due to meteoroids less than a century in age and are due to "trails" from 55P/Tempel-Tuttle which are within (8+-6)x10^-4 A.U. of Earth's orbit at the time of these storms. The storm producing segment of the stream are perturbed into Earth-intersection through distant, direct perturbations primarily from Jupiter. The relative average flux in the stream decreases by 2-3 orders of magnitude in the first hundred years after ejection. Comparison of the width of theoretical storm profiles with those observed constrain ejection velocities to be less than 20 m/s with an average near 5 m/s. It is found that Jupiter controls the development and evolution of the stream over long-time scales, while radiation pressure and initial ejection velocities are significant factors in the first century after ejection. The age of the annual component of the stream is found to be of order 1000 years.
Results of the 1998 International Leonid Observation Campaign
T. Baayraa, D. Batmunkh, B. Bekhtur (Research Centre of Astronomy and Geophysics, Mongolian Academy of Sciences, Mongolia), D. Babcock, R. Worsfold (Centre for Research in Earth and Space Technology, York University, Toronto ON, Canada), LtCol M. Bedard, Col. S.P. Worden (HQ USAF/XOR 1480 Air Force Pentagon, Washington, D.C, U.S.A), M. Beech (Campion College, The University of Regina, SK, Canada), P. Brown, M. Campbell, J. Jones, A.R. Webster (Dept. of Physics and Astronomy, University of Western Ontario, London, ON Canada), M. Connors (Centre for Natural and Human Science, Athabasca University, Athabasca AB Canada), Maj. R. Correll (HQ AFSPC/XP, Rep to NASA HQ, NASA HQ, Washington D.C. U.S.A), K.J. Ellis (Communications Research Centre, Ottawa, ON Canada), G. Garradd (PO Box 157, Tamworth NSW, Australia), P. Gural (SAIC, Arlington, VA USA), R.L. Hawkes, A. LeBlanc (Dept. of Physics, Mount Allison University, Sackville, NB Canada), LtCol D. Jewell, Maj. B Tilton (HQ AFSPC/XPC, Colorado Springs, CO, U.S.A.), R.H. McNaught (PO Box 650, Coonabarabran, NSW, Australia), S. Molau, J. Rendtel (International Meteor Organization, Potsdam, Germany), Lt. T. Montague (AFRL/VSSS, Kirtland AFB, NM U.S.A), Maj. J. Thorne (SMC, Los Angeles AFB, CA, U.S.A.)
We present results of observations of the 1998 Leonids from sites in Mongolia and Australia using electro-optical, multi-frequency radar and photographic techniques. The flux profile of the shower using each of these techniques for the days nearest the maximum are presented and discussed. The distribution of particles within the stream as a function of time from both electro-optical and radar observations will also be given and the values compared. Analysis of beginning heights from electro-optical and photographic observations are used to estimate the presence of a volatile fraction in Leonid meteoroids. An estimate of the fraction of incident Leonids detected as a function of radar frequency will also be given and compared to the correction factors computed on the basis of the height distribution of the TV Leonid meteor population.
Composition and structure of the 1998 Leonids from video spectroscopy
J. Borovicka (Ondrejov Observatory, Czech Republic), R. Stork (Ondrejov Observatory), J. Bocek (Ondrejov Observatory)
We report the results of a low resolution meteor spectroscopy experiment performed during the 1998 international Leonid Multi-Instrument Aircraft Campaign. A video camera with image intensifier and spectral grating was run onboard the FISTA aircraft flying over the eastern Pacific on November 17, 1998, 15-21 UT. During this time, a secondary maximum of the Leonid shower with zenith hourly rate of about 200 occurred (Arlt R., WGN 26, 239, 1998). The maximum was rich in relatively faint meteors and is believed to consist of material ejected from the parent comet Tempel-Tuttle relatively recently. During the 6 hours of observations, 119 meteor spectra were recorded, at least 98 of them being Leonids. The meteor magnitudes range from -5 to +3, the dispersion is 1.2 nm/pixel in the first order and the wavelength coverage is 380-880 nm, with maximum sensitivity near 550 nm. The Leonid spectra obtained in this experiment were compared with spectra of Perseids and other meteors obtained with a sensitive TV camera at the Ondrejov observatory in the recent years.
Leonid spectra were found to be very rich in lines of oxygen, nitrogen and nitrogen molecule. About 2/3 of radiated energy in the given wavelength range is due to atmospheric emissions. This can be ascribed to the large velocity of Leonid meteors. About 1/6 of the energy is radiated as thermal continuum and only another 1/6 is due to the emissions of the meteoric vapor. Only the lines of Mg, Na, Fe, and Ca are bright enough to provide information on meteoroid composition. Their relative abundances are, within the errors, consistent with normal solar system abundances. However, another effect was found in Leonids which is not present in Perseids: The sodium line is relatively bright at the beginning but almost disappears at the middle of the trajectory. The effect is less pronounced in bright meteors than in faint meteors and suggests that Leonid meteoroids are very loose and can be described in terms of the dustball model (Hawkes and Jones, MNRAS 173, 339, 1975). Small meteoroids disintegrate completely before the onset of ablation and volatile sodium material is therefore released from the whole volume and can evaporate substantially earlier than silicate grains. A search for organic carbon bearing molecules in Leonid spectra yielded no convincing detection.
The Faintest Visual Meteors of the 1998 Leonids: Airborne Observation with the High-Definition Digital Video Cameras over the East China Sea
H. Yano (NASA Johnson Space Center), D. Bretz (Hernandez Engineering), S. Abe, J. Watanabe (National Astronomical Observatory of Japan), O. Iiyama (Nippon Meteor Society), Y. Fujii, R. Nakamura (Kobe University)
On the 17th November 1998 (UT), we conducted 6+ hours observation of the faintest visual meteors of the Leonids with high-definition digital video cameras (HD-TV) with image-intensifiers developed by NHK, onboard two aircraft at ~7-13 km altitudes over the East China Sea, as a part of NASA's Leonid Multi-instrument Aircraft Campaign. Advantages of this system over conventional videos were higher light sensitivity, finer spatial resolution, and digitized 10-bit images that enable semi-automated post processing without suffering from down conversion. The motivation was to measure the flux of the faintest (i.e., +8-10 apparent magnitudes) Leonid meteors and their trajectory distribution, which were otherwise impossible to study accurately.
One of the HD-TV cameras was used for three different fields-of-view pointed 40 degree above the horizon; the detection limit of meteors for the best set-up was ~+10th magnitude. Another was fixed with a 50 mm / f1 lens pointing at the zenith on the second airplane, for evaluating the time variation of the meteor flux down to the +9th magnitude. Also performed was a velocity analysis of representative meteors using a commercially available motion tracking software package.
As the results, even when time approached to the predicted peak of the main component (i.e., 19-20h on the day UT), we found no significantly enhanced activities. Also the population index value started to drop at the magnitudes +6~+8, which were still above the detection limit of this HD-TV set-up. This implies that at least the main component of the 1998 Leonids was poor in the smallest meteoroids, which impact probability of hitting one of the ~600 operational satellites was no larger than an order of 1 %. This is consistent with an estimate of the high gas/dust ratio of the Comet Tempel-Tuttle based on the ground observation conducted by our team in February 1998.
ARE MOST METEOROIDS REALLY DUSTBALLS?
Amy Fisher (Mount Allison University, Sackville, NB Canada), Robert Hawkes (Mount Allison University, Sackville, NB Canada), Ian Murray (Mount Allison University, Sackville, NB Canada), Margaret Campbell (University of Western Ontario, London, ON Canada), Andrew LeBlanc (Mount Allison University, Sackville, NB Canada)
Analysis of light curves of faint meteors seem to suggest that most meteoroids are collections of large numbers of grains at least some of which are released prior to the onset of intensive ablation. We would expect such grains, unless extremely uniform in physical properties, to be aerodynamically separated during flight, and therefore to produce wake (instantaneous light production from an extended spatial region). We present theoretical results for wake production as a function of grain mass distribution, height of separation and velocity. In addition, we have obtained observational results from a new study which used short duration intensified CCD detectors to search for wake in sporadic meteors. The system employed coaxial intensified CCD cameras at each of two stations, one system utilizing a rotating shutter and one not at each station. The majority of meteors showed no statistically significant wake, although several examples of apparent transverse separation of light production regions were found. We also present results of detailed light curve analysis from coaxial intensified CCD systems used on the NASA Airborne Leonid MAC 1998 program. These provide some support for the idea of transverse spread in the light production region.
Leonid Trails and Lasers -- A Video
Jack Drummond (USAF), Mike Kelley (Cornell University), Chet Gardner (University of Illinois)
During the 1998 Leonid meteor shower, the University of Illinois' sodium lidar was used at the Starfire Optical Range on Kirtland AFB, NM, to measure the impact of the passage of a meteor on the number density, temperature, and velocity of sodium atoms at 100km altitude. A 200W copper vapor laser (CVL) was also used in an attempt to measure back-scatter from particulates in the contrails of the Leonids. Guided by a human observer, the Starfire's 3.5m telescope, used as a receiver for the lidar, was steered onto the lingering trails of meteors and a 5 degree wide Xybion camera, attached to the headring of the telescope, recorded the scene. A 15 minute highlight video will be presented showing the evolution of the lingering trails as well as the lidar and the CVL probing them.
Almost all of the meteors that produced lingering trails greatly enhanced the naturally occurring sodium layer at 100km. The lingering trails generally appeared as evanescent smoke rings that evolved rather quickly, with the path of the meteor marked by a double walled, optically thin tube. One meteor, however, was radically different. The brightest meteor of the night (about -4.5 magnitude) produced NO sodium enhancement. Its contrail appeared optically thick, turbid, had right angles over its path, lingered the longest, more than 30 min, and simply dissipated, rather than evolved. These trails, and their evolution, will be featured in the video.
Numerical Modeling of Chemiluminescence in Meteor Trains
Craig Kruschwitz (Cornell University), Michael Kelley (Cornell University), Chester Gardner (University of Illinois), Jack Drummond (USAF)
During the 1998 Leonids meteor shower several multi- intrument observations of persistent meteor trains were made from the Starfire Optical Range in Albuquerque, New Mexico, and from a secondary site in Placitas, New Mexico. Measurements were made of Na density, temperature, and Na airglow intensity. In addition, various cameras captured images and videos of the trains, several of which were observed for more than 30 minutes. Of particular interest are the Na airglow and density measurements since they allow us to quantify the contribution of Na airglow to the observed luminescence, long hypothesized but never proven to be a result of Na airglow chemistry. Here, an attempt is made to numerically model train luminescence. Cylindrical symmetry is assumed, and observed values of the Na density, temperature, and diffusion constants are used. Also, a mechanism for the formation of the "double-line" structure, characteristic of most of the observed trains, is proposed, and this effect is modeled.
Physical structure of faint LLLTV meteors
Margaret Campbell (Dept of Physics and Astronomy, University of Western Ontario, London,ON, Canada N6A 3K7), R.L. Hawkes (Physics Department, Mount Allison University, Sackville, NB Canada E4L 1E6)
Analysis of light curves of Leonid meteors from the 1998 shower is presented. A statistical analysis of the position of maxima and steepness of the curves has been performed for comparison with other showers. The shapes of the light curves are compared to theoretical shapes produced from numerical simulations using the classical equations of meteor ablation. Various physical structures have been modelled: solid bodies, objects which fragment and clusters of individual grains. Various chemical compositions including mixes of stone and iron have also been investigated.
The Leonids 1998 over Japan - Storm Component or Not ? -
J. Watanabe (Nat.Astron. Obs. Japan), S. Abe (Nat.Astron. Obs. Japan), T. Nakamura (Kyoto University), H. Yano (Inst. Space Aero. Sci.), O. Iiyama (Nippon Meteor Soc.)
The Leonid meteor shower was expected to show higher than usual activity, especially at around 20h UT on November 17 in 1998, which corresponds to the nodal crossing of the Earth. This was appropriate observing window for Aisan region. We conducted several ground-based observations in Japan, including the radar observation. Altough a high-sensitivity TV monitor indicated a weak increase of the activity toward the end of the observation, the number of visual meteors did not show any clear increasing trends. While several reports indicated the existence of the "storm component" around the nodal crossing time, they may be due to the overcorrection. The averaged influx of the Leonids was 1.4 X 10^-5 km^-2 s^-1 (magnitude <+8) during our observation. We describe the results of the analysis of our ground-based observations, focusing on the time profile of the activity.
The Leonid meteor shower observation project by senior-high school students in Japan
B.Suzuki ((Misato Technological High School), Japan Leonids'98 executive committee ()
At the night on 1998 November 17, joint observation on the Leonid meteors with many senior-high school students, which was planed by the Leonids '98 executive committee, was held in Japan. One of the objects of this observation was to clarify the spatial distribution of the meteoroids ejected from the parent comet 55P/Tempel-Tuttle by counting the number of meteors with the naked eyes all over Japan. Students succeeded in counting meteors at more than 200 observation points, and efficiency of the observation network was confirmed. Another object of this joint observation was to bring the opportunities of having a fieldwork and of thinking nature to the field of education. Through communing with night sky, observing meteors with colleagues all over Japan, planing the observation procedure and thinking the treatment of acquired data, we expected that participators tackled the joint observation independently and understood the nature and the processes of scientific research. Moreover, we expected participation of not only teachers but also amateurs, researchers and staff in social educational facilities, so that the project would become the base on the future astronomical community in Japan. We would like to spread a plan of Leonids'99 in the world. Please contact to by e-mail ; email@example.com , firstname.lastname@example.org Our homepage ; http://www.leonids.net/ , http://www.leonids.net/eng/
MULTIPLE FRAGMENTATION OF A LEONID METEOR
N. Bhandari (Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India.)
The Impact of Leonid 1998 Meteor Stream on the Vertical Distribution of Dust Particles in the Atmosphere.
N. Mateshvili (Abastumani Astrophysical Observatory), I. Mateshvili (Abastumani Astrophysical Observatory), G. Mateshvili (Abastumani Astrophysical Observatory), L. Geonjian (Abastumani Astrophysical Observatory)
The electrophotometric measurements of the twilight scattered light were carried out in Abastumani Astrophysical Observatory, Republic of Georgia, during Leonides 1998. The observations were made on 11; 12; 20; 21 of November (evening twilights) and on 17; 21; 22 of November (morning twilights) . The ratios were calculated of the altitudinally dependent scattered sun light intensities between 20 km and 140 km for all the above observations over a reference curve obtained as a polynomial approximation of the light intensity to altitude dependence of Nov. 11. The last was considered as a day free of Leonid disturbances. The ratios of Nov. 11 and 12 were found to be close to the statistically derived curve reflecting the routine aerosol stratification (I. Mateshvili et al., 1998 ) . The ratio curve of Nov. 17, morning, showed a unique event. The normally stratified aerosol distribution was totally destroyed. The atmosphere from 20 to 140 km was uniformly loaded with dust. The ratios at 50, 80 and 120 km were 1.5, 2 and 3 times higher than those of Nov.11. A partial recovery of the normal aerosol stratification could be observed by Nov. 20, though higher ratios remained. They were almost normal on Nov.21 but those of the stratospheric aerosol layer which exceeded the corresponding ratios of Nov. 11 by factor 1.4.
I. Mateshvili, G. Mateshvili, N. Mateshvili. (1998) Measurement of the vertical aerosol distribution in the middle atmosphere by the twilight sounding method. J. Aerosol Sci., Vol. 29, No 10, pp. 1189-1198.
Possibility of radio detection of molecules produced during meteoroid entry - HCN observations of the Leonids in 1998 and 1999.
Despois, D. (Observatoire de Bordeaux, France), Biver, N. (IfA, Hawaii, USA), Ricaud, Ph. (), Dobrijevic, M. (), Baron, Ph. (), Kieken, J. (), Selsis, F. (), Jacq, T. (), Billebaud, F. (Observatoire de Bordeaux, France), Lis, D. (Caltech, USA), Crovisier, J. (Observatoire de Paris-Meudon, France), Paubert, G. (IRAM Granada, Spain), Schneider, N. (Univ. of Koeln, Germany and Obs. de Grenoble, France), Matthews, H. (JAC, Hawaii, USA)
Interplanetary dust particles (IDPs) bring about 20,000 tons of solid matter to the Earth each year. They release/produce at least a similar amount of gases in the upper atmosphere. Assessing the chemical composition and amount of these gases is important for the study of the IDPs, the physical processes during the entry phase, the aeronomy of the Earth upper atmosphere, and for the exobiological questions about the origin of carbon and prebiotic molecules delivered to the Early Earth.
We first present crude estimations of the line intensity which can be expected, for observations both from ground radio telescopes or from the ODIN satellite for several likely molecules. Expected line shapes are computed over a wide range of frequencies and molecules. Vertical profiles can be estimated from the data using the code we developped for ODIN atmospheric data analysis.
We then present a search for a variation of mesospheric HCN conducted in November 1998 at the time of the return of the most remarkable periodic meteor shower, the Leonids, using several radio telescopes (JCMT, IRAM 30m, Bordeaux 2.5m, CSO).
Finally we describe tentative observation plans for the 1999 Leonid meteor shower.
Discovery of the Distant Lunar Sodium Tail and its Enhancement Following the 1998 Leonid Meteor Shower
Steve Smith (Center for Space Physics, Boston University), Jody Wilson (Center for Space Physics, Boston University), Jeffrey Baumgardner (Center for Space Physics, Boston University), Michael Mendillo (Center for Space Physics, Boston University)
Nighttime measurements using a bare CCD all-sky imaging system have detected the presence of an extensive region of neutral sodium emission in the direction of the anti-solar/lunar points. The emission was observed to occur during the nights of 21-22 August and 18-20 November, 1998 UT, centered on the new Moon period. The most likely interpretation is that the Moon is the source of the neutral sodium, making this the first detection of the lunar sodium tail out to a distance of hundreds of lunar radii. The greater brightness of the emission feature in November is attributed to the Leonid meteor shower which peaked on 17 November 1998, less than two days before new Moon.
Very precise orbits of Leonid meteors
H. Betlem (Dutch Meteor Society), J. van 't Leven (Dutch Meteor Society), P. Spurny (Ondrejov Observatory), P. Jenniskens (SETI Institute)
Ground stations in support of Leonid MAC were set up in China. Purpose was to measure the meteor flux in timezones +1 and +2 from Okinawa, Japan, and to measure precise meteor trajectories and orbits using photographic and video techniques, in an ongoing program to study the dynamics of meteor stream formation and evolution.
Four sites were equipped with about 15 35mm cameras with f1.8/50-80mm optics, owned and operated by 19 amateur observers of the Dutch Meteor Society. Two sites were in the Beijing area, with Xing Long Observatory as the main station. Two others were set up near Delingha with the Qinghai Radio Observatory as the main station.
Here we report the first photographic results from the Beijing area (Xing Long and Lin Ting Kou sites).
The dynamical evolution of a cylindrical persistent train
David Nugent (SETI Institute), Sandy Osborough (Chippenham, UK), Peter Jenniskens (SETI Institute)
An exceptional long-lasting persistent train of a bright Leonid was recorded with an intensified video camera in the night of November 16/17 from a location in the UK. The train is remarkable in that a hollow cylindrical structure is apparent along its entire track, and because two parts of the train remain stationary with respect to the stars. The dynamical evolution of those parts have been studied, resulting in the first data on the expansion timescale of persistent trains and the time evolution of the thickness of the bright cylinder walls.
Impressions of the 1998 Leonid Multi-Instrument Aircraft Campaign
P. Jenniskens (SETI Institute), Steve Butow (USAF/129th RQS, ACC)
The various experimental techniques deployed in the 1998 Leonid Multi-Instrument Aircraft Campaign will be highlighted by means of a series of photographs taken during the mission.
PROPOSAL FOR CURRICULUM COMPONENT FOR JUNIOR HIGH AND HIGH SCHOOL PHYSICS / EARTH SCIENCES CLASSES INVOLVING METEOR / CELESTIAL OBSERVATIONS IN RURAL SCHOOLS.
A.A. Mardon. Antarctic Institute of Canada. P.O. Box 1223, M.P.O., Edmonton, Alberta, T5J-2M4. CANADA. E-Mail: email@example.com
|This page was last modified on July 26, 1999 by
Peter Jenniskens and Casper ter Kuile