Detailed visual observations and modelling of the 1998 Leonid shower

We present a detailed activity profile for the 1998 Leonid shower from visual observations. The shower displayed at least two distinct components – a broad component peaking between 2344 and 2350, and two narrower filaments near 23521 and 23533 probably of younger origin based on modelling results. This dual-peaked structure in the flux profile has peak fluxes to a limiting magnitude of +6.5 of 0.03 Leonid km⁻² h⁻¹. The distribution of particles also changes dramatically across the stream in 1998, with large meteoroids dominating the early peak and smaller meteoroids relatively more abundant near the time of the nodal passage of the comet. Detailed comparison of the observed activity with models in 1998 shows that the early component comes from material ejected between 500 and 1000 yr ago. Our modelling results suggest that the later dual peaks are caused by high- β meteoroids with large ejection velocities released during the 1932 and 1965 passages of Comet 55P/Tempel–Tuttle.     

Observations of the 1985 Giacobinid meteor shower in Japan

A strong meteor shower was observed by members of the Nippon Meteor Society (NMS) during the evening of October 8, 1985, across Japan which was believed to be a display of the Giacobinids, the first strong display in Japan since the 1965 Leonids. Favorable weather allowed several types of observations to be made. Most observations were visual but some were made telescopically or photographically. FM radio and TV camera techniques were also used. The data obtained by observations and by photography are analyzed below. Main results are as follows:

• 1.(1) Considering the position of the radiant and the orbital elements of the meteors, the shower was undoubtedly the Giacobinids.
• 2.(2) The maximum zenithal hourly rate of the shower was 154 at 10^h10^m UT. This rate was, however, much lower than 5000 during the display of the Giacobinids in 1933 or in 1946.

     

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.     

Determination of the solar X-ray spectrum by using the atmospheric extinction

Indications about the spectral distribution of the solar radiation below 20 Å are obtained by comparing the atmospheric extinction of the solar radiation measured by three ion chambers in the satellites SOLRAD 7 and 8.The data refer to July 5, 6 and 8, 1965 and July 23, 1966 when the satellites passed from light to darkness into or out of the earth's shadow.The spectral intensity distribution is shown for the four days, and a comparison is made between active and quiet days.     

Application of CORSIKA Simulation Code to Study Lateral and Longitudinal Distribution of Fluorescence Light in Cosmic Ray Extensive Air Showers

In this paper, we used CORSIKA code to understand the characteristics of cosmic ray induced showers at extremely high energy as a function of energy, detector distance to shower axis, number, and density of secondary charged particles and the nature particle producing the shower. Based on the standard properties of the atmosphere, lateral and longitudinal development of the shower for photons and electrons has been investigated. Fluorescent light has been collected by the detector for protons, helium, oxygen, silicon, calcium and iron primary cosmic rays in different energies. So we have obtained a number of electrons per unit area, distance to the shower axis, shape function of particles density, percentage of fluorescent light, lateral distribution of energy dissipated in the atmosphere and visual field angle of detector as well as size of the shower image. We have also shown that location of highest percentage of fluorescence light is directly proportional to atomic number of elements. Also we have shown when the distance from shower axis increases and the shape function of particles density decreases severely. At the first stages of development, shower axis distance from detector is high and visual field angle is small; then with shower moving toward the Earth, angle increases. Overall, in higher energies, the fluorescent light method has more efficiency. The paper provides standard calibration lines for high energy showers which can be used to determine the nature of the particles.     

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.     

Interpretation of the time structure of the EAS disc measured by the GREX/COVER_PLASTEX experiment

Simulation results for the time structure of the extensive air shower disc are presented and compared with data from the GREX/COVER_PLASTEX experiment. The distribution of the arrival times at various distances from the shower core and the contributions from the secondary particles to the shape of the distribution are described. The main parameters of the distribution, the mean time of arrival τ and the standard deviation σ, reflect the shower disc profile and thickness. The dependence of the shower profile and thickness on the energy and mass of the primary particle initiating the shower as well as on its inclination angle is discussed. The influence of the experimental conditions on the disc profile and thickness measured by the GREX/COVER_PLASTEX experiment is analysed and a parametrization of the average profile and thickness is given.     

Analysis of a 30-year series of photoelectric observations of RY Tauri. I. Search for possible periodicities

Searches for periodic variations in the brightness of RY Tauri over various time intervals are conducted on the basis of photoelectric observations made by the author at the Crimean Station of the Shternberg State Astronomical Institute (GAISh) from 1965 through 2000 and of data published by others. The total duration of the series of observations is 12500 days. The existence of a long cycle lasting about 2000 days is confirmed. Short periods owing to rotational modulation of the brightness are not always present. During a time when the brightness of the star was increasing in 1966, a period of 7.5 days showed up. The detection of fluctuations which might be identified with rotational modulation evidently depends on the star’s level of brightness. In 1993 and 1996, respectively, periods of 20.0 and 29.4 days were discovered which are most likely caused by inhomogeneities in the circumstellar disk.     

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.     

On activity periods of the April Lyrids

The activity of the Lyrid meteor shower is analyzed by visual observations in the interval 1900–2007. Processing of observations over a long time interval confirmed the presence of two periods of activity of the shower, of 12 and 60 years. These periods almost coincide with the period and five times Jupiter’s orbital period, i.e., 11.8 and 59.3 years, respectively, suggesting the possible influence of Jupiter on the shower structure. High activity of the shower is observed when the epoch of observations and the commensurate moment coincide with the orbital period of Jupiter and can be registered in the next 1–2 years. The increased activity of Lyrid by visual observations suggests that ZHR exceeds 30 meteors per hour. The modeling of activity profiles of showers for different minimum masses of meteoroids has shown that there is a correlation between the longitude of the node from the orbit with the mass of particles.     

Differential rotation of the solar electron corona

Autocorrelation analyses of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii, during 1964–1967 have established average yearly rotation rates of coronal features as a function of latitude and height above the limb. At low latitudes the corona was found to rotate at the same rate as sunspots but at higher latitudes was consistently faster than the underlying photosphere. There were differences as large as 3–4% in the rate at specific latitudes from year to year and between the two hemispheres. In 1967 a nearly constant rotation was found for heights ranging from 1.125 to 2.0 R ₀. For 1966 there was a more complicated pattern of height dependence, with the rate generally decreasing with height at low latitudes and increasing at high latitudes.At Hawaii Institute of Geophysics.     

Correlated features of arrival time and angle-of-incidence distributions of EAS muons

Various features and correlations of the arrival time and angle-of- incidence distributions of muons of extensive air showers (EAS) are studied by analyses based on Monte-Carlo simulations of the EAS development by using the air shower simulation code CORSIKA. Trends and dependencies of the temporal dispersion of the EAS muon component on shower size and distance from the shower core are displayed by the distribution of the arrival time and angle of incidence of the first muon, of the mean and median of the single shower distribution. Special attention is called to multi-correlations in observations at different radial distances from the shower core. These ‘radial’ correlations provide additional information for the discrimination of different EAS primaries, while the correlation of muon arrival time and angle-of-incidence is shown to improve the mass separation only insignificantly. This feature does not basically change, when arrival times and angles of incidence are displayed by transformed quantities like ‘muon production heights’.     

The gas to dust ratio in NGC 6523

On the basis of an electron density distribution deduced from radio-observations, the gas to dust ratio in NGC 6523 is determined, and found to be constant throughout the nebula. The results are in agreement with the observations made by O'Dellet al. (1966).     

Outlying plasmasphere structure detected by whistlers

Whistlers recorded at Eights ($\text{L ? 4}$) and Byrd ($\text{f ? 7}$), Antarctica have been used to study large-scale structure in equatorial plasma density at geocentric distances $\text{?3–6}\text{R}{}_{\mathrm{E}}$. The observations were made during conditions of magnetic quieting following moderate disturbance. The structures were detected by a “scanning” process involving relative motion, at about one tenth of the Earth's angular velocity or greater, between the observed density features and the observing whistler station or stations. Three case studies are described, from 26 March 1965, 11 May 1965 and 29 August 1966. The cases support satellite results by showing outlying high density regions at $\text{?4–6}\text{R}{}_{\mathrm{E}}$ that are separated from the main plasmasphere by trough-like depressions ranging in width from $\text{?0.2}$ to 1 R_E. The structures evidently endured for periods of 12 hr or more. In the cases of deepest quieting their slow east-west motions with respect to the Earth are probably of dynamo origin. The cases observed during deep quieting (11 May 1965 and 29 August 1966) suggest the approximate rotation with the Earth of structure formed during previous moderate disturbance activity in the dusk sector. The third case, from 26 March 1965, may represent a structure formed near local midnight. The reported structures appear to be closely related to the bulge phenomenon. The present work supports other experimental and theoretical evidence that the dusk sector is one of major importance in the generation of outlying density structure. It is inferred that irregularities of the type reported here regularly develop near 4–5 R_E during moderate substorm activity. This research suggests that at least a major class of the density structures that develop near 4 R_E are tail-like in nature, joined to the main body of the plasmasphere. The apparent disagreement with Chappell's results from OGO 5, which are interpreted as showing regions of “detached” plasma beyond 5 R_E, may be related to the pronounced spatial structure of electric fields observed in high-latitude ionospheric regions that are conjugate to the magnetospheric regions in which the OGO-5 observations were made.     

Taurid resonant-swarm encounters from two decades of visual observations

Enhanced Taurid activity in terms of visual meteor and fireball rates has been found in 1988, 1991, 1995, 1998 and 2005 data. The years of heightened activity are shown to be unequivocally linked to the encounters of swarms of resonantly trapped particles in the Taurid meteoroid stream according to the model proposed by Asher & Clube. While the annual activity level of the Taurid meteor shower in terms of zenithal hourly rate  (ZHR) is 7.8 ± 1.2  , swarm year activity typically reaches ZHRs of 12–17. The annual fraction of fireballs is below 1 per cent; in swarm years, this fraction is as high as 2.4–4.6 per cent near the maximum of the Taurid activity period.     

Time structure of individual extensive air showers

Extensive air showers detected by the GREX array have been sampled by means of highly segmented 8 m² bakelite RPC in the GREX/COVER_PLASTEX experiment. Delay distributions of particles with respect to the first arriving particle in the EAS front at PeV energies have been analysed for individual events in the core distance range of 0–100 m. It is shown that both mean arrival time and EAS front thickness in individual showers fluctuate strongly and cannot be a good measure of the distance from the EAS axis in a 0–100 m core distance interval.

Individual distributions have been compared with integrated inclusive distributions measured in the same experiment. Results indicate that the width of the individual distribution is systematically less than that of the inclusive distribution. It means that the bulk of particles in individual showers arrive as a relatively compact group delayed by different time intervals from the first arriving particle. Such fluctuations of the arrival time for most of the shower particles may be the consequence of large fluctuations in the shower longitudinal development.

Comparison with CORSIKA Monte Carlo simulations confirmed the difference between the mean width of inclusive and individual arrival time distribution. It revealed also the presence in the experiment of the excessive train of delayed particles near the shower core. This train is obviously due to the non-relativistic low energy hadrons most abundant in the shower core region.     

The 1998 outburst and history of the June Boötid meteor shower

The June Boötid meteor shower (sometimes referred to as the Draconids) surprised a number of regular and casual observers by an outburst with maximum zenithal hourly rates (ZHRs) near 100 on 1998 June 27 after a quiescent period of several decades. A total of 1217 June Boötid meteors were recorded during regular visual meteor observations throughout this outburst. An average population index of r =2.2±0.10 was derived from 1054 shower magnitude estimates. The broad activity profile with ZHR>40 lasting more than 12 h and the large spread of apparent radiants in 1998 resemble the 1916 and 1927 outbursts. The peak time is found to be at about λ _⊙=95°.7 (2000.0); peak ZHRs are of the order of 200, whereas reliable averages reach only 81±7. The period of high ZHRs covered by a single observer implies a full width at half-maximum of 3–4 h. The resulting maximum flux of particles causing meteors brighter than +6.5 mag is between 0.04 and 0.06 km⁻² h⁻¹. The average radiant from photographic, radar and visual records is α =224°.12, δ =+47°.77. The observed activity outbursts in 1916, 1927 and 1998 are not related to the orbital period or the perihelion passages of the parent comet 7P/Pons–Winnecke. These are probably a consequence of the effects of the 2:1 resonance with Jupiter.     

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.     

The Takysie Lake,B.C., Stones: Meteorites or Moon Rock?

Abstract. The first of the fusion crusted Takysie Lake, British Columbia, stones were found by Nininger in June, 1965. A field trip to determine the number and distribution of the unusual stones got underway in July, 1966. An intensive search of all accessible areas resulted in collection of 55 specimens with a total weight of 127.6 pounds. The apparent southern, western, and northern limits of the strewn field were established. The eastern limits could not be learned because of the heavily forested terrain. The unique structure and compositional characteristics of the stones indicate either a new variety of meteorite or a secondary meteorite of lunar origin. Suggestions are made for further investigation.