Video Observations of the 2006 Leonid Outburst

We carried out double station observations of the Leonid meteor shower outburst, which occurred in the morning hours of November 19, 2006. Using image-intensified cameras we recorded approximately 100 Leonid meteors. As predicted, the outburst was rich especially in fainter meteors. The activity profile shows that the peak of the outburst occurred at 4:40 ± 0:05 UT. The maximum reached flux was 0.03 meteoroids km⁻² hod⁻¹ for meteors brighter than +6.5 magnitude.     

Leonid meteor spectrum from 110 to 860 nm

During the Leonid meteor shower on 18 November 1999, the five spectrographic imagers onboard the Midcourse Space Experiment (MSX) satellite recorded the first complete meteor spectra from 110 to 860 nm. The observation occurred at 00:23:36.2 UT, at which time the satellite was pointed at a tangent altitude of 100 km over 37.2°N and 78.2°E. The spectrograph slits were oriented approximately parallel to the horizon at a tangent altitude of 100 km, and the meteor passed approximately perpendicular through the slits’ fields of view. All five spectrographic imagers observed the passage of a bright object (m_v < −2.8 at 100 km) and each recorded several frames of data. In the visible, common meteor emissions were observed from iron, sodium, and oxygen. However, the ultraviolet spectrum displayed a wealth of more intense features, some of which actually caused saturation in the spectrographs. The most intense features appeared between 220 and 300 nm and are attributed to neutral and singly ionized iron and ionized magnesium. Some unknown emissions, possibly from an unidentified molecular species such as iron oxide, appear between 180 and 220 nm. In the far ultraviolet from 110 to 130 nm, oxygen and nitrogen features appear in the spectrum, with some features from ionized iron and magnesium. In particular, the FUV spectrum showed an intense emission from hydrogen Lyman alpha and a much weaker emission from what appeared to be neutral carbon. The atmospheric emissions can be associated with the heating within the meteor shock, while the metallic emissions originate from the fireball of the meteor proper. The ultraviolet emissions were much stronger than those in the visible and near-infrared parts of the spectrum. The energy of emissions in the ultraviolet (110 < λ < 337 nm) exceeded the energy of the visible (337 < λ < 650 nm) by a factor of at least 5.     

Observations of the 2001 Leonid meteor shower using VHF meteor radar

Every year the Earth crosses or passes near one of the dust trails left by Comet 55P/Tempel-Tuttle in its pass through the Solar System every 33.2 years. This produces a meteor shower Commonly called the Leonid. The 2001 Leonid meteor shower is one of the strongest in recent years. We present observations made by the 50 MHz all-sky meteor radar located at the Platteville Atmospheric Observatory in Colorado (40° N, 105° W). The spatial and temporal distributions of the meteor activity detected by the radar during the 2001 Leonid shower differs from the observed sporadic activity detected by VHF radars. Estimation of the radiant flux of the meteor shower of the shower by a well-known methodology is presented, and the intensity of the phenomena is discussed.     

Analysis of historical meteor and meteor shower records: Korea, China, and Japan

We have compiled and analyzed historical Korean meteor and meteor shower records in three Korean official history books, Samguksagi which covers the three Kingdoms period (57 B.C.-A.D. 935), Goryeosa of Goryeo dynasty (A.D. 918-1392), and Joseonwangjosillok of Joseon dynasty (A.D. 1392-1910). We have found 3861 meteor and 31 meteor shower records. We have confirmed the peaks of Perseids and an excess due to the mixture of Orionids, north-Taurids, or Leonids through the Monte Carlo test. The peaks persist from the period of Goryeo dynasty to that of Joseon dynasty, for almost one thousand years. Korean records show a decrease of Perseids activity and an increase of Orionids/north-Taurids/Leonids activity. We have also analyzed seasonal variation of sporadic meteors from Korean records. We confirm the seasonal variation of sporadic meteors from the records of Joseon dynasty with the maximum number of events being roughly 1.7 times the minimum. The Korean records are compared with Chinese and Japanese records for the same periods. Major features in Chinese meteor shower records are quite consistent with those of Korean records, particularly for the last millennium. Japanese records also show Perseids feature and Orionids/north-Taurids/Leonids feature, although they are less prominent compared to those of Korean or Chinese records.     

A comparison of detection sensitivity between ALTAIR and Arecibo meteor observations: Can high power and large aperture radars detect low velocity meteor head-echoes

Meteor head-echo observations using High Power and Large Aperture (HPLA) radars have been routinely used for micrometeor studies for over a decade. The head-echo is a signal from the radar-reflective plasma region traveling with the meteoroid and its detection allows for very precise determination of instantaneous meteor altitude, velocity and deceleration. Unlike specular meteor radars (SMR), HPLA radars are diverse instruments when compared one to another. The operating frequencies range from 46 MHz to 1.29 GHz while the antenna configurations changes from 18,000 dipoles in a 300 m×300 m square array, phase arrays of dipoles to single spherical or parabolic dishes of various dimensions. Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07] recently showed, by utilizing a head-echo plasma-based model, the presence of instrumental biases in the ALTAIR VHF radar system against detecting meteors produced by very small particles (<1 μg) moving at slow (∼20 km/s) velocities due to the low head echo radar cross-section (RCS) associated with these particles. In this paper we apply the same methodology to the Arecibo 430 MHz radar and compare the results with those presented by Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07]. We show that, if the methodology applied by Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi:10.1016/j.icarus.2006.09.07] is accurate, for particles at least 1 μg or heavier, while the bias may exist for the ALTAIR measurements, it does not exist in the Arecibo data due to its greater sensitivity.     

The Third Peak of the 1998 Leonid Meteor Shower

1 INTRODUCTIONThe Leonid meteor shower is a well-known periodic meteor shower. Its history is tied upwith the development of the theory of meteor stream astronomy itself. It was the very st.rongshowers of 1799 and 1833 that played a sghficant pat in the recoghtion of the ealstence ofmeteoroid streams. These evellts started the obse~ions of Leoaid meteor shower and broughtabout the birth of meteoritiCS. It is known that the Leould parent comet, 55P/Tempel-TUttle,has an orbital period a…     

狮子座流星雨1999年照相观测的分析

对1999年11月19日拍摄的两张狮子座流星胶片进行了分析研究照相观测比目观测记录了更多的定量信息计算了流星在胶片上显露时必须满足的运动角速度条件,求出了流星起始点仰角、流星结束点与辐射点的角距离、流星运动的角速度以及流星路径的弧长等并且得出流星在大气中的烧蚀时间仅0 65秒左右,即烧蚀的路径长约40 50公里通过在扫描仪上得到的黑白图像的处理,求得两颗流星的照相星等分别为-10.3 ± 0.2和-4.8±0.2.由此可以得到它们的质量和电子线密度.给出的处理方法,也可用于其他流星的照相观测资料处理.并且,对流星观测使用的照相镜头也进行了讨论.     

First definitive observations of meteor shower particles using a high-power large-aperture radar

We present the first clear observations of meteor shower activity from meteor-head echoes detected by a high-power large-aperture radar (HPLAR). Such observations have been performed at the Jicamarca VHF radar using its interferometric capabilities allowing the discrimination of meteor shower echoes from the much more frequent sporadic meteors. Until now, HPLARs were unable to distinguish meteor shower from the much more common sporadic meteor ones. In this work we have been able to detect and characterize the η-Aquariids (ETA) as well as the Perseids (PER) showers. The shower activity is more conspicuous for the ETA than for the PER shower due to the more favorable geometry. Namely, PER meteors come from low elevation angles, experiencing more filtering due to the combined Earth-atmosphere-radar instrument. In both cases, there is an excellent agreement between the measured mean velocity of the shower echoes and their expected velocity, within a fraction of 1 km s⁻¹. Besides the good agreement with expected visual results, HPLARs observe meteors with a variety of particles sizes and masses, not observed by any other technique. Taking into account the different viewing volumes, compare to optical observations Jicamarca observes more than 1000 times more ETA meteors. Our results indicate that Jicamarca and other HPLARs are able to detect the echoes from meteor showers, but without interferometric capabilities such populations are difficult to identify just from their velocity distributions, particularly if their velocity distributions are expected to be similar to the more dominant distributions of sporadic meteors.     

Characterization of the Meteoroid Spatial Flux Density during the 1999 Leonid Storm

The November 18, 1999 Leonid storm was rich in meteors and well observed by airborne intensified video cameras aimed low in the sky which enabled enhanced meteor counts over ground-based observations. The two- and three-dimensional distribution of meteoroids was investigated for signs of clustering that could provide evidence of meteoroid fragmentation shortly after lift-off from the parent comet 55P/Tempel-Tuttle, or much later due to space weathering. Analysis of the video tapes yields a refined estimation of the mass ratio during the peak of s = 1.65 and spatial flux density of 0.5 particles/km² greater than those causing visual magnitude +6.5 during the 5 min centered around the peak of the storm. Furthermore, the projection of the individual trails into three-dimensional Heliocentric coordinates, shows non-homogeneity of the stream on spatial scales from hundreds to thousands of kilometers.     

Photographic Observations of the 1996 Leonid Fireballs in Japan

Several Leonid fireballs were successfully photographed by the Japanese Fireball Network and by other observers in Japan on 16 November, 1996. A totals of seven of these were simultaneously observed from two or more stations, from which the orbital and physical data were deduced. The radiant of these fireballs were very small, only 0.1°, similar to that of the 1991 Perseids. The 1996 Leonids showed a lower magnitude distribution index similar to those obtained in the 1961 and 1965 Leonids. All of these showers occurred before perihelion passage of the parent comet. We conclude that we have already encountered the elongated front part of the dust trail of the Leonid parent comet, where the trail is probably composed of larger dust particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sporadic meteor sources as observed by the Jicamarca high-power large-aperture VHF radar

We present, for the first time, the main sources of sporadic meteors as inferred from meteor-head echoes obtained by a high-power large-aperture radar (HPLAR). Such results have been obtained at the Jicamarca HPLAR (11.95° S, 76.87° W, 1° dip angle). Observations are based on close to 170,000 meteors detected in less than 90 h spread over 14 days, between November 2001 and February 2006. Meteors with solar orbits are observed to come from basically six previously known sources, i.e., North and South Apex, Helion, Anti-Helion, and North and South Toroidal, representing ∼91% of the observations. The other ∼9% represents meteors with observed velocities greater than the Sun's escape velocity at 1 AU, most of them of extra-solar origin. Results are given before and after removing the Earth's velocity and the sources are modeled with two-dimensional Gaussian distributions. In general, our results are in very good agreement with previously known sources reported by Jones and Brown [Jones, J., Brown, P.G., 1993. Mon. Not. R. Astron. Soc. 265, 524-532] using mainly specular meteor radar (SMR) data gathered over many years and different sites. However, we find slightly different locations and widths, that could be explained on the basis of different sensitivities of the two techniques and/or corrections needed to our results. For example, we find that the North and South Apex sources are well defined and composed each of them of two collocated Gaussian distributions, one almost isotropic with ∼10° width and the other very narrow in ecliptic longitude and wide in ecliptic latitude. This is the first time these narrow-width sources are reported. A careful quantitative analysis is needed to be able to compare the strengths of meteor sources as observed with different techniques. We also present speed and initial altitude distributions for selected sources. Using a simple angular sensitivity function of the combined Earth-atmosphere-radar instrument, and an altitude selection criteria, the resulting meteor sources are in better qualitative agreement with the results obtained with SMRs.     

Observations of interplanetary meteoroids with TIRA

The Tracking and Imaging RAdar (TIRA) at the Research Establishment for Applied Science (FGAN) was used in the L-band (1.33 GHz) to observe the Leonid shower in 1999. The radar beam was pointed directly into the radiant in the constellation Leo to receive “head echoes” from meteoroids when they ablate in the atmosphere at altitudes around 100 km. Two hundred and eighty-seven meteors were observed during 21 h in the early hours of November 17 and 18, 1999. The individual velocities, radiants and rough heliocentric orbits are calculated. Criteria are derived from optically observed Leonids which are then applied to decide whether an echo was created by a Leonid or a background meteoroid. However, in most cases the accuracy in the observational data is not good enough to allow for a clear distinction. Only for 100 meteors the velocity errors were less than 10 km/s. Out of those, 71 could be excluded on a 3σ level to be a Leonid (95 are excluded on a 1σ level). This confirms the theory that the Leonids have dominantly sizes of optical meteoroids with no significant extension in the lower mass range. Therefore, the risk of meteoroid impacts on spacecraft does not increase considerably during a Leonid storm. Background measurements 9 days after the Leonids maximum were taken in 2001 which corroborated the overall results obtained in 1999.     

Separation of meteor streams from the sporadic background

A cluster analysis procedure has been used to estimate the fraction of the sporadic interlopers (sporadis bias) identified as stream members among the observed meteor orbits. Using the artificial meteor orbits with the same distribution as the observed one, the sporadic bias is estimated for the given threshold value of the orbital similarityD _c. It has been shown that in case of the radio meteor catalogues theD _c values given by the formula proposed in Southworth and Hawkins (1963)and in Lindblad (1971) correspond to the sporadic bias of 8–21%. For the five radio meteor catalogues the values ofD _c corresponding to the fixed bias equal to 10% and 15% are given.     

On the Origin of the 1999 Leonid Storm as Deduced from Photographic Observations

Photographic multi-station observations of 18 Leonid meteorsobtained by the Spanish Photographic Meteor Network are presented. For each meteoroidthe radiant position, trajectory data and orbital parameters are discussed and compared totheoretical radiant positions and orbital elements of particles ejected from 55P/Tempel–Tuttle in 1899.We discuss the role of mean velocity imprecision in the dispersion of some orbital parameters,specially the semimajor axis. Finally, by applying the dust trail theory we have adjusted the1999 Leonidstorm orbits to a defined semimajor axis value to test the quality of photographic observations.     

Updates to the MSFC Meteoroid Stream Model

The Marshall Space Flight Center (MSFC) Meteoroid Stream Model simulates particle ejection and subsequent evolution from comets in order to provide meteor shower forecasts to spacecraft operators for hazard mitigation and planning purposes. The model, previously detailed in Moser and Cooke (Earth Moon Planets 95, 141 (2004)), has recently been updated; the changes include the implementation of the RADAU integrator, an improved planetary treatment, and the inclusion of general relativistic effects in the force function. The results of these updates are investigated with respect to various meteoroid streams and the outcome presented.     

Distribution and properties of fragments and debris from the split Comet 73P/Schwassmann-Wachmann 3 as revealed by Spitzer Space Telescope

During 2006 March-2007 January, we used the IRAC and MIPS instruments on the Spitzer Space Telescope to study the infrared emission from the ensemble of fragments, meteoroids, and dust tails in the more than 3° wide 73P/Schwassmann-Wachmann 3 debris field. We also investigated contemporaneous ground-based and HST observations. In 2006 May, 55 fragments were detected in the Spitzer image. The wide spread of fragments along the comet’s orbit indicates they were formed from the 1995 splitting event. While the number of major fragments in the Spitzer image is similar to that seen from the ground by optical observers, the correspondence between the fragments with optical astrometry and those seen in the Spitzer images cannot be readily established, due either to strong non-gravitational terms, astrometric uncertainties, or transience of the fragments’ outgassing. The Spitzer data resolve the structure of the dust comae at a resolution of ∼1000 km, and they reveal the infrared emission due to large (mm to cm size) particles in a continuous dust trail that closely follows the projected orbit. We detect fluorescence from outflowing CO₂ gas from the largest fragments (B and C), and we measure the CO₂:H₂O proportion (1:10 and 1:20, respectively). We use three dimensionless parameters to explain dynamics of the solid particles: the rocket parameter α is the reaction force from day-side sublimation divided by solar gravity, the radiation pressure parameter β is the force due to solar radiation pressure divided by solar gravity, and the ejection velocity parameter ν is the particle ejection speed divided by the orbital speed of the comet at the time of ejection. The major fragments have ν>α>β and are dominated by the kinetic energy imparted to them by the fragmentation process. The small, ephemeral fragments seen by HST in the tails of the major fragments have α>ν>β and are dominated by rocket forces (until they become devolatilized). The meteoroids along the projected orbit seen by Spitzer have β∼ν?α and are dominated by radiation pressure and ejection velocity, though both influences are much less than gravity. Dust in the fragments’ tails has β?(ν+α) and is dominated by radiation pressure.     

An accuracy estimation of the World CCD asteroid observations in the years 1999-2005

The MPC database of the asteroid observations (each position from near 20 millions) was used in analysis of observational accuracy for more than 300 active world observatories both professional and amateur. The values of the “Mean error of a single observation” σ (for α,δ) were derived based on the Pulkovo method of accuracy estimation. These values may be used for observatory weight assignment in the orbital improvement procedures. The accuracy of the best amateur observations is proved to be comparable with professional one (σ=±0^″.20). The detailed results in electronic format are accessible from the first author.