A new asteroid-associated meteor shower and notes on comet-asteroid connection

The calculation of the orbit of the potentially hazardous Asteroid 2001 YB₅ suggests a possible meteor shower around January 7.5, 2002 UT. Video observations revealed an unidentified radiant around the predicted maximum time, at RA=121.5°, Dec=+11.5°(for solar longitude 287.30°). Visual observers also reported unusually high rates from that region on the same night, indicating that 2001 YB₅ did produce a weak meteor shower. Furthermore, it is noticed that 2001 YB₅ is a rare B-type asteroid in same spectral class with Asteroid (3200) Phaethon, the parent body of the only previously known asteroid-associate meteor shower, Geminids.     

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.     

Perseid meteor stream as observed in 1993

Presented are results of Perseid 1993 meteor shower from radar observation at Ondejov observatory. Investigation of the shower activity profiles in four echo duration intervals proved the position of dominant peak at solar longitude L = 138.°8±0.°05 (epoch 1950.0) followed by series of secondary maxima positions of which depend on examined echo duration class. Extremely low value of the mass distribution indexs = 1.27 ± 0.01 near the maximum activity peak associated with high proportion of fragmenting particles leads to the suggestion that meteor particles concentrated in this filament are younger than those which form the other parts of the stream.     

Radar Observations of Leonid Meteor Shower 2003

Observations carried out during Leonid meteor shower 2003, by using Indian MST radar (13.46^N, 79.18^E; dip 12.5^N) are used to determine the number density of meteoroids through the cross section of the meteor streams. Cross sections are calculated for a number of classes of echo duration (particle size). They are also used to determine the relative flux of the shower in particle size ranges producing radar meteor echoes having durations <0.4 s, 0.4–1 s and >1 s. Mean activity profiles along the Earth's passage through the stream show a systematic change of the peak activity and the width of the stream depending on the distribution of echo durations across the stream. The patterns of mass distribution index s are presented and discussed.     

A Method for Determining the Coordinates of Meteor Shower Radiants from Meteor Radar Goniometric Data

We discuss a new method for measuring the coordinates of meteor shower radiants from meteor radar data. The method uses a high accuracy of radar goniometer measurements of one of the angular coordinates for meteor radiants and collective properties of incident meteor showers. It is based on a computer technology of searching for the coordinates of radiants using the intersections of meteor position lines on the celestial sphere and filtering nonrandom combinations of these intersections. The method allows the following: to detect meteor showers with a rate of more than 5 per day of observations and to separate meteor groups from different meteor showers with different radiants and velocities. The method makes it possible to increase the angular resolution from 10° × 10° achieved with a quasi-tomographic technique to 2° × 2°, with a prospect of a further increase in the accuracy through the individual reduction of separated meteor groups. We use the reduction of one-day-long observations during maximum activity of the Geminids meteor shower in 1993 to illustrate the potentialities of the method. We show an example of detecting a weak meteor shower that was active during December 1993.     

CAMS: Cameras for Allsky Meteor Surveillance to establish minor meteor showers

First results are presented from a newly developed meteoroid orbit survey, called CAMS – Cameras for Allsky Meteor Surveillance, which combines meteor detection algorithms for low-light video observations with traditional video surveillance tools. Sixty video cameras at three stations monitor the sky above 31° elevation. Goal of CAMS is to verify meteor showers in search of their parent comets among newly discovered near-Earth objects.This paper outlines the concept of operations, the hardware, and software methods used during operation and in the data reduction pipeline, and accompanies the data release of the first batch of meteoroid orbits. During the month of November 2010, 2169 precisely reduced meteoroid trajectories from 17 nights have an error in the apparent radiant of the trajectory <2° and error in speed <10%. Median values of the error are 0.31° and 0.53 km/s, respectively, sufficient to resolve the intrinsic dispersion of annual meteor showers and resolve minor showers from the sporadic background. The limiting visual magnitude of the cameras is +5.4, recording meteors of +4 magnitude and brighter, bright enough to stand out from the mostly fainter sporadic meteors detected as under dense radar echoes.CAMS readily detected all established showers (6) active during the clear nights in November. Of the showers that needed confirmation, we confirm the theta Aurigids (THA, IAU#390), the chi Taurids (CTA, IAU#388), and the omicron Eridanids (OER, IAU#338). We conclude that the iota November Aurigids (IAR, IAU#248) are in fact the combined activity of the theta Aurigids and chi Taurids, and this shower should be dismissed from the list. Finally, there is also a clustering consistent with the zeta Cancrids (ZCN, IAU#243), but we cannot exclude that this is lower perihelion dust belonging to the Orionid shower.Data are submitted to the IAU Meteor Data Center on a semi-regular basis, and can be accessed also at http://cams.seti.org.     

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.     

Meteor stream activity. III. Measurement of the first in a new series of Leonid outburst

Abstract— In 1994 November, a shower of bright Leonid meteors signaled what is likely the first meteor outburst of Leonids associated with the upcoming return of comet P/Tempel-Tuttle to perihelion. Measurements of meteor activity and the meteor brightness distribution are presented. By comparing the present observation with those of past Leonid returns, a forecast is made of the time, the duration, the intensity, and the mean meteor brightness of Leonid outbursts that may occur if previously observed patterns are repeated in the forthcoming years.     

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…     

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.     

The relationship between the semi-major axis, mass index and age of the Leonid meteor shower

Owing to sublimation of ice, comet nuclei eject dust particles when they are near to the sun. Those particles assume velocities and then vary their orbits to ones similar to that of the comet. The most notable difference between the orbit of the parent comet and those of the particles is their semi-major axes. This difference (Δ a ) has been widely used in modern meteor shower predictions. Observational evidence of the distribution showed that it is a function of Δ a , and the age of the dust trail. However, the relation is not well known. In this paper, a simplified relation between Δ a , the mass index ( s ) and the age of the dust trail is presented, taking the instance of a recent Leonid meteor shower.     

近20年来狮子座流星雨预报进展

对近20年来狮子座流星雨的预报工作，进行了系统的阐述和分析。1998年Tempel-Tuttle彗星的回归，再度带来了狮子座流星雨的观测热，也大大促进了对狮子座流星雨预报工作的研究与验证。有的研究在时间预报准确度方面已显示出其模型的优越性，有的在流星雨的强度方面显示出一定的准确度。指出了两大类不同的方法实际上是在三维空间强调了不同的方面。将不同方法的优势结合起来，可能会使流星雨的预报更加成熟。     

Radar sporadic meteor rates and solar activity

The correlation of sporadic meteor rates from radar observations in January, August, and December non-show-er periods in 1958–2000, and relevant solar activity represented by the solar relative number, R, is investigated. Similar analysis of the December sporadic period was already presented by Simek 1999, and Pecina. Complete analysis indicates high correlation of both phenomena with sporadic meteor counts curve following that of solar activity after 1.5–2 years in the mean eleven year solar cycle with the correlation index exceeding 70%. This result supports the large volume of observing material of the Ondřejov meteor radar in the above mentioned span covering almost four solar cycles. 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.     

The Leonid outburst of 1996

There is strong anticipation that the Leonid meteor shower could produce storm-level activity in 1998 and/or 1999. The well-documented Leonid outburst in 1996 and the more poorly observed one in 1994 have been taken by many observers to imply that a storm is imminent, This article explores the possible relationship between the 1996 outburst in activity and possible Leonid storms. The curve of activity is found to be much closer to that of normal activity, although with greater hourly rates, than it is to the very brief, steeply rising activity curve of a storm. It is probable that the 1996 outburst is thus completely unrelated to any future storm which may appear.     

Spaceborne ultraviolet 251–384 nm spectroscopy of a meteor during the 1997 Leonid shower

Abstract— We used the ultraviolet to visible spectrometers onboard the midcourse space experiment to obtain the first ultraviolet spectral measurements of a bright meteor during the 1997 Leonid shower. The meteor was most likely a Leonid with a brightness of about‐2 magnitude at 100 km altitude. In the region between 251 and 310 nm, the two strongest emission lines are from neutral and ionized magnesium. Ionized Ca lines, indicative of a hot T ? 10 000 K plasma, are not detected. The Mg and Mg+ line intensity ratio alone does not yield the ionization temperature, which can be determined only by assuming the electron density. A typical air plasma temperature of T = 4400 K would imply a very high electron density: n_e = 2.2 times 10¹⁸ m‐³, but at chondritic abundances of Fe/Mg and Si/Mg ? 1. For a more reasonable local‐thermodynamic‐equilibrium (LTE) air plasma electron density, the Mg and Mg+ line ratio implies a less than chondritic Fe/Mg = 0.06 abundance ratio and a cool non‐LTE T = 2830 K ionization temperature for the ablation vapor plasma. The present observations do not permit a choice between these alternatives. The new data provide also the first spectral confirmation of the presence of molecular OH and NO emission in meteor spectra.     

Flux of very faint Leonid meteors observed with a 3 meter liquid mirror telescope intensified charge‐coupled device system

Abstract— We have used a 3.0 m diameter liquid mirror telescope (LMT) coupled to a microchannel plate image‐intensified charge‐coupled device (CCD) detector to study the 1999 Leonid meteor shower. This is the largest aperture optical instrument ever utilized for meteor detection. While the observing system is sensitive down to stars of +18 astronomical magnitude under optimum conditions, when corrections for meteor motion are applied the majority of the meteors collected fall in the absolute magnitude range from +5 to +10, corresponding to photometric masses from about 10^?7 to 10^?9 kg. This is largely due to the fact that the field of view of the LMT was only 0.28°, so that only a small portion of the luminous meteor trail was recorded. While the flux of these small (1.4 times 10^?9 kg) Leonid meteors is low (on the order of one Leonid meteor per hour per square kilometer perpendicular to the Leonid), we do have clear evidence that the Leonid stream contains particles in the mass range studied here. The data showed a possibly significant peak in Leonid flux (9.3 ± 3.5) for the 1 h period from 11:00 to 12:00 u.t. 1999 November 17 (solar longitude 234.653 to 234.695, epoch 2000.0), although the main trend of these results is a broad low‐level Leonid activity. There is evidence that small meteoroids are more widely distributed in the Leonid stream, as would be expected from cometary ejection stream models. As would be expected from an extrapolation of mass distribution indices for brighter meteors, the vast majority of meteors at this size are sporadic. The LMT is a powerful detector of sporadic meteors, with an average non‐Leonid detection rate of more than 140 meteor events per hour.     

Meteoric activities during the 11th century

We have analysed the meteor records in the chronicles that describe the era of the Song dynasty ( ad 960–1279). The data are complementary to the record-vacant 10th century of the Koryo dynasty ( ad 918–1392). The annual activity of sporadic meteors analysed shows a generic sinusoidal behaviour as in modern observations. In addition, we have also found that there are two prominent meteor showers, one in August and the other in November, appearing on the fluctuating sporadic meteors. The date of occurrence of the August shower indicates it to be the Perseids. By comparing the date of occurrence of the November shower with those of the Leonid showers of the Koryo dynasty, recent visual observations and the world-wide historical meteor storms, we conclude that the November shower is the Leonids. The regression rate of the Leonids is obtained to be     days per century, which agrees with recent observations.     

THE LEONIDS BY RADAR—1957 TO 19681

Radar observations of the Leonid meteor shower, made near Ottawa during the years from 1957 to 1968 inclusive, are analyzed and reduced to give comparative flux rates. A strength classification has been made in terms of the ratio of shower rates to background rates. The relative strengths found by radar, showing marked variability from year to year, are confirmed by analysis of available visual observations. There is also great variation in the distribution of particle sizes. The high rates of the 1966 return were accompanied by a relatively high percentage of small particles. In 1965 there was a much higher proportion of large particles, and the high rates of 1961 showed a mass or size distribution intermediate between that of 1966 and of 1965.     

Comet Tempel-Tuttle and the Leonid meteors

The distribution of dust surrounding periodic comet Tempel-Tuttle has been mapped by analyzing the associated Leonid meteor shower data over the 902–1969 interval. The majority of dust ejected from the parent comet evolves to a position lagging the comet and outside the comet's orbit. The outgassing and dust ejection required to explain the parent comet's deviation from pure gravitational motion would preferentially place dust in a position leading the comet and inside the comet's orbit. Hence it appears that radiation pressure and planetary perturbations, rather than ejection processes, control the dynamic evolution of the Leonid particles. Significant Leonid meteor showers are possible roughly 2500 days before or after the parent comet reaches perihelion but only if the comet passes closer than 0.025 AU inside or 0.010 AU outside the Earth's orbit. Although the conditions in 1998–1999 are optimum for a significant Leonid meteor shower, the event is not certain because the dust particle distribution near the comet is far from uniform. As a by-product of this study, the orbit of comet Tempel-Tuttle has been redetermined for the 1366–1966 observed interval.