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  • 1
    Electronic Resource
    Electronic Resource
    Search for Organic Matter in Leonid Meteoroids (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 71-80 
    Details
    ISSN: 1573-0794
    Keywords: Astrobiology ; CN ; exobiology ; Leonids 1999 ; meteors ; meteoroids ; origin of life ; spectroscopy ; ultraviolet
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Near-ultraviolet 300–410 nm spectra of Leonid meteoroids were obtained in an effort to measure the strong B → X emission band of the radical CN in Leonid meteor spectra at 387 nm. CN is an expected product of ablation of nitrogen containing organic carbon in the meteoroids as well as a possible product of the aerothermochemistry induced by the kinetic energy of the meteor. A slit-less spectrograph with objective grating was deployed on FISTA during the 1999 Leonid Multi-Instrument Aircraft Campaign. Fifteen first-order UV spectra were captured near the 02:00 UT meteor storm peak on November 18. It is found that neutral iron lines dominate the spectrum, with no clear sign of the CN band. The meteor plasma contains less than one CN molecule per 3 Fe atoms at the observed altitude of about 100 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017021929075
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  • 2
    Electronic Resource
    Electronic Resource
    Observations of Leonid Meteors Using a Mid-Wave Infrared Imaging Spectrograph (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 81-92 
    Details
    ISSN: 1573-0794
    Keywords: Ablation ; Leonids 1998 ; meteors ; meteoroids ; mid-IR emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We report broadband 3–5.5 µm detections of two Leonid meteors observed during the 1998 Leonid Multi-Instrument Aircraft Campaign. Each meteor was detected at only one position along their trajectory just prior to the point of maximum light emission. We describe the particular aspects of the Aerospace Corp. Mid-wave Infra-Red Imaging Spectrograph (MIRIS) developed for the observation of short duration transient events that impact its ability to detect Leonid meteors. This instrument had its first deployment during the 1998 Leonid MAC. We infer from our observations that the mid-wave IR light curves of two Leonid meteors differed from the visible light curve. At the points of detection, the infrared emission in the MIRIS passband was 25 ± 4 times that at optical wavelengths for both meteors. In addition, we find an upper limit of 800 K for the solid body temperature of the brighter meteor we observed, at the point in the trajectory where we made our mid-wave IR detection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017026032709
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  • 3
    Electronic Resource
    Electronic Resource
    Leonid Storm Flux Analysis from One Leonid Mac Video AL50R (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 221-247 
    Details
    ISSN: 1573-0794
    Keywords: Clustering ; flux ; fragmentation ; Leonids 1999 ; meteor ; meteoroid ; optimal video pointing ; satellite impact hazard ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A detailed meteor flux analysis is presented of a seventeen-minute portion of one videotape, collected on November 18, 1999, during the Leonid Multi-instrument Aircraft Campaign. The data was recorded around the peak of the Leonid meteor storm using an intensified CCD camera pointed towards the low southern horizon. Positions of meteors on the sky were measured. These measured meteor distributions were compared to a Monte Carlo simulation, which is a new approach to parameter estimation for mass ratio and flux. Comparison of simulated flux versus observed flux levels, seen between 1:50:00 and 2:06:41 UT, indicate a magnitude population index of r = 1.8 ± 0.1 and mass ratio of s = 1.64 ± 0.06. The average spatial density of the material contributing to the Leonid storm peak is measured at 0.82 ± 0.19 particles per square kilometer per hour for particles of at least absolute visual magnitude +6.5. Clustering analysis of the arrival times of Leonids impacting the earth's atmosphere over the total observing interval shows no enhancement or clumping down to time scales of the video frame rate. This indicates a uniformly random temporal distribution of particles in the stream encountered during the 1999 epoch. Based on the observed distribution of meteors on the sky and the model distribution, recommendations are made for the optimal pointing directions for video camera meteor counts during future ground and airborne missions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017030431743
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of 1998 and 1999 Leonid Light Curve Morphology and Meteoroid Structure (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 351-367 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; dust ; Leonids 1999 ; lightcurves ; meteoroids ; meteors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Photometric low-light level video observations of 1999 Leonid storm meteors have been obtained from two airborne platforms during the Leonid multi-instrument aircraft campaign (Leonid MAC). The 1999 Leonid light curves tend to be skewed towards the end point of the trajectory, while the 1998 Leonid light curves were not. The variation in the light curves from 1998 and 1999 can be explained as an overall reduction in the mass distribution index, α from ∼ 1.95 in 1998 to ∼ 1.75 in 1999. We have interpreted this behaviour as being either indicative of a gradual loss of the "glue" that keeps the grains together, or the fact that the meteoroids sampled in 1998 had a different morphological structure to those sampled in 1999. The early fragmentation of a dustball meteoroid results in a light curve that peaks sooner than that predicted by classical single body ablation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017003019448
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  • 5
    Electronic Resource
    Electronic Resource
    Time Resolved Spectroscopy of a Leonid Fireball Afterglow (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 399-428 
    Details
    ISSN: 1573-0794
    Keywords: Afterglow ; debris ; dust ; H ; meteor ; persistent train ; spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two video spectra of a meteoric afterglow were obtained for the first time during the 1999 Leonid aircraft campaign. The train was produced by a −13 magnitude Leonid fireball at a relatively low height between 91-75 km. The meteor spectrum has a strong hydrogen emission, proportional to 10–20 II atoms per one Fe atom The train spectrum consisted of a red continuum, yellow continuum, and about 50 atomic lines between 3700–9000 Å. The yellow continuum, possibly due to NO2, was also detected in the persistent train. The red continuum is interpreted as a thermal radiation of dust from meteoric debris at about 1400 K. Evidence for secondary ablation is found in the afterglow. The atomic lines decayed within seconds of the meteor. The lines of Fe I, Mg I, Na I, Ca I, Ca II, Cr I, Mn I, K I, and possibly Al I were present in the glow together with the 5577 Å forbidden O I line. The gas temperature in the train was close to 5000 K at the beginning and decayed to 1200 K within two seconds. However, thermal equilibrium was not satisfied for all populated levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017071524899
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  • 6
    Electronic Resource
    Electronic Resource
    Jet-Like Structures and Wake in Mg I (518 nm) Images of 1999 Leonid Storm Meteors (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 379-389 
    Details
    ISSN: 1573-0794
    Keywords: Fragmentation ; jet-like ; Leonids 1999 ; meteoroids ; meteors ; structures ; wake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Small meteoric fragments are ejected at significant transverse velocities from some (up to ∼8%) fast Leonid meteors. We reach this conclusion using low light intensified image measurements obtained during the 1999 Leonid Multi-Instrument Aircraft Campaign. High spatial resolution, narrow band image measurements of the Mg I emission at 518 nm have been used to clearly identify jet-like features in the meteor head that are the same as first observed in white light by LeBlanc et al. (1999). We postulate that these unusual structures are caused by tiny meteoroid fragments (containing metallic grains) being rapidly ejected away from the core meteoroid as the constituent glue evaporates. Marked curvature observed in the jet-like filaments suggest that the parent meteoroids are spinning and as the whirling fragments are knocked away by the impinging air molecules, or by grain-grain collisions in the fragment ensemble, they ablate quickly generating an extended area of structured luminosity up to about 1–2 km from the meteoroid center. Fragments with smaller transverse velocity components are thought to be responsible for the associated beading evident in the wake of these unusual Leonid meteors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017063322173
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  • 7
    Electronic Resource
    Electronic Resource
    Precise Trajectories and Orbits of Meteoroids from the 1999 Leonid Meteor Storm (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 277-284 
    Details
    ISSN: 1573-0794
    Keywords: Comet dust trial ; dispersion ; Leonids 1999 ; meteor ; meteor orbit ; meteor trajectory ; orbital dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Photographic multi-station observations of 47 Leonid meteors are presented that were obtained from two ground locations in Spain during the 1999 meteor storm. We find an unresolved compact cluster of radiants at α = 153.67 ± 0.05 and δ = 21.70 ± 0.05 for a mean solar longitude of 235.282 (J2000). The position is identical to that of the Nov. 17/18 outburst of 1998, which implies that both are due to comet 55P/Tempel-Tuttle's ejecta from 1899. We also find a halo which contains about 28% of all meteors. The spatial distribution of radiant positions appears to be Lorentzian, with a similar fraction of meteors in the profile wings as the meteor storm activity curve.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017070313938
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  • 8
    Electronic Resource
    Electronic Resource
    1997 Leonid Shower from Space (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 305-312 
    Details
    ISSN: 1573-0794
    Keywords: Flux ; Leonids 1999 ; meteors ; meteor shower ; MSX ; population index ; space
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In November 1997, the Midcourse Space Experiment satellite (MSX) was deployed to observe the Leonid shower from space. The shower lived up to expectations, with abundant bright fireballs. Twenty-nine meteors were detected by a wide-angle, visible wavelength, camera near the limb of the Earth in a 48-minute interval, and three meteors by the narrow field camera. This amounts to a meteoroid influx of 5.5 ± 0.6 10−5 km−2 hr−1 for masses 〉 0.3 gram. The limiting magnitude for limb observations of Leonid meteors was measured at Mv = −1.5 magn. The Leonid shower magnitude population index was 1.6 ± 0.2 down to Mv = −7 magn., with no sign of an upper mass cut-off.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017034815755
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  • 9
    Electronic Resource
    Electronic Resource
    The 1999 Leonid Multi-Instrument Aircraft Campaign - An Early Review (1998)
    Springer
    Earth, moon and planets 82-83 (1998), S. 1-26 
    Details
    ISSN: 1573-0794
    Keywords: Airborne astronomy ; astrobiology ; chemistry ; comets ; composition ; elves ; exobiology ; instrumental techniques ; Leonid MAC ; Leonids 1999 ; lower thermosphere ; meteoroids ; meteor storm ; meteors ; mesosphere ; orbital dynamics ; satellite impact hazard ; sprites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two B707-type research aircraft of the 452nd Flight Test Squadron at Edwards Air Force Base were deployed to study the Leonid meteor storm of 1999 over the Mediterranean Sea on Nov. 18. The mission was sponsored by various science programs of NASA, and offered an international team of 35 researchers observing conditions free of clouds and low altitude extinction at a prime location for viewing the storm. This 1999 Leonid Multi-Instrument Aircraft Campaign followed a similar effort in 1998, improving upon mission strategy and scope. As before, spectroscopic and imaging experiments targeted meteors and persistent trains, but also airglow, aurora, elves and sprites. The research aimed to address outstanding questions in astrobiology, planetary science, astronomy, and upper atmospheric research. In addition, USAF co-sponsored the mission to provide near real-time flux measurements for space weather awareness. First results are presented in these issues of Earth, Moon, and Planets in preparation for future missions that will target the exceptional Leonid returns of 2001 and 2002. An early review of the scientific achievements in the context of campaign objectives is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017020106785
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  • 10
    Electronic Resource
    Electronic Resource
    Probing the structure of cometary ice (1995)
    Springer
    Origins of life and evolution of the biospheres 25 (1995), S. 3-19 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Computer simulations of bulk and vapor deposited amorphous ices are presented. The structure of the bulk low density amorphous ice is in good agreement with experiments on pressure disordered amorphous ice. Both the low density bulk ice and the vapor deposited ices exhibit strong ordering. Vapor deposition of hot (300 K) water molecules onto a cold (77 K) substrate yields less porous ices than deposition of cold (77 K) water molecules onto a cold subtrate. Both vapor deposited ices are more porous than the bulk amorphous ice. The structure of bulk high density amorphous ice is only in fair agreement with experimental results. Attempts to simulate high density amorphous icevia vapor deposition were not successful. Electron diffraction results on vapor deposited amorphous ice indicate that the temperature of the nucleation of the cubic phase depends upon the amount of time between the deposition and the onset of crystallization, suggesting that freshly deposited ice layers reconstruct on times of the order of hours. The temperature dependence of the microporosity of the vapor deposited amorphous ices might affect laboratory experiments that are aimed at simulating astrophysical ices in the context of the origin of prebiotic organic material and its transport to the Earth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581570
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