Meteor Radiants Research Articles

KINEMATIC PARAMETERS, PHYSICAL CHARACTERISTICS, AND CHEMICAL COMPOSITION OF SELECTED METEOR BODIES

Background. Meteoroids can reach the Earth and penetrate its atmosphere creating meteor phenomena. Kinematic parameters, physical characteristics, and chemical compositions of the observed meteor bodies provide information about the properties of their parent bodies — comets and asteroids. On the other hand, these parameters can reflect the physical conditions of meteor- oids staying in different parts of the Solar System and beyond. Methods. The meteor data analyzed in this work were obtained from observations using the automatical video and spectral meteor patrol (AVSMP) of the Institute of Astronomy of V. N. Karazin Kharkiv National University. The methods of meteor astronomy and spectroscopy make it possible to determine the kinematic parameters, physical properties, and chemical com- position of the meteoroids that we studied. Results. The paper presents the research results of meteors brighter than 0m that were recorded by the multi-stations method. These meteors also have spectral observations. For the selected 12 meteors, we obtained the coordinates of meteor radiants on the celestial sphere, the parameters of the atmospheric trajectories of meteor bodies, and the heliocentric orbital parameters of the observed meteoroids for the epoch (J2000). The extra-atmospheric masses of meteoroids were determined from photometric data. The identified emission lines detected in meteor spectra were analyzed. The software developed by the authors of this paper for me- teor spectra processing was used. Qualitative and quantitative analyses of the chemical composition of meteor bodies were carried out. During the quantitative analysis, the values of the relative intensities of the Fe I-15, Mg I-2, and Na I-1 lines were determined. Conclusions. Kinematic parameters and elements of heliocentric orbits presented in this work indicate that the observed me- teor bodies belong to meteor showers and their comets, such as Perseids, Leonids, and Southern Taurids. Some meteor bodies are sporadic. The calculated masses of meteoroids have some scatter of values, but they are generally consistent with observa- tions of other authors in the range of absolute values of the meteor brightness -2m…+1.5m. It was found that some of the studied meteor bodies are Fe-poor or Na-poor in their chemical composition.

Meteor Radar for Investigation of the MLT Region: A Review

This is an introductory review of modern meteor radar and its application to the measurement of the dynamical parameters of the Mesosphere Lower Thermosphere (MLT) Region within the altitude range of around 70 to 110 km, which is where most meteors are detected. We take a historical approach, following the development of meteor radar for studies of the MLT from the time of their development after the Second World War until the present. The application of the meteor radar technique is closely aligned with their ability to make contributions to Meteor Astronomy in that they can determine meteor radiants, and measure meteoroid velocities and orbits, and so these aspects are noted when required. Meteor radar capabilities now extend to measurements of temperature and density in the MLT region and show potential to be extended to ionospheric studies. New meteor radar networks are commencing operation, and this heralds a new area of investigation as the horizontal spatial variation of the upper-atmosphere wind over an extended area is becoming available for the first time.

On the question of constructing the distribution of the flux density of meteoroids over the celestial sphere in ground-based single-position radar measurements of meteor activity and velocity: The experience of past years

The construction of the distribution of the flux density of meteor bodies over the celestial sphere is necessary for solving problems of meteor astronomy and others. To construct such distributions, experimental data on the coordinates of meteor radiants are needed. Meteor radars provide determination of the coordinates of the radiant in the presence of one transmitter and three spaced receivers. In this research, we are talking about ground-based meteor observations of the number of meteors using single-station meteor back-skatter radars as simpler than measurements of meteor radiants. In the 1950–80s in Kharkiv (Ukraine), active meteor radar research was carried out, both simple single-station and complex with remote points. The authors in the 1980s were participants in the meteor international program GLOBMET (Kashcheev, 1982; Roper, 1990). At that time, they modified an algorithm for calculating the flux density of meteor bodies over the heliocentric celestial sphere by number, range and velocity for radar observations with using single-station meteor backscatter. An algorithm was developed for dividing the celestial sphere into regions with a combination of “celestial” and “antenna” regions with a binding of a meteor to the antenna region in radar observations with a narrowly directed antenna without goniometr. This algorithm was applied to specific equipment for measuring the number of meteors by the Kharkiv Meteor Automated Radar System (MARS), 31.1 MHz. The correctness of the algorithm was confirmed by constructing the density distribution of the incident flux over the celestial sphere based on measurements in October-December 1989. The distributions are constructed using two methods for approximating the amplitude-time characteristics of signals. The results represent the experience of past years, which may be of interest as a scientific and technical solution.

The distributions of meteor substance in the Galactic coordinate system according to the MARS radar database and SonotaCo's TV catalogue

Research goal: the search for "extrasolar" sources of meteor substance in the Earth atmosphere using positions of meteor radiants in the Galactic coordinate system; comparison of the distributions of meteor substance in the Galactic coordinate system from the radar database of MARS (Meteor Radar Automated System in Kharkiv) and from the SonotaCo's TV catalogue. Hyperbolic meteors can be associated with the "extrasolar" space. In such case, properties of their "extrasolar" motion may manifest both in the orbital parameters of Earth meteors and in their Galactic coordinates. Extensive observations can give the answer to such hypothesis. Two large databases of meteoroid orbital elements exist: MARS radar database, obtained in 1972–1978 in Ukraine (Kashcheyev and Tkachuk, 1980), and SonotaCo's TV catalogue obtained in 2007–2013 in Japan (SonotaCo, 2009). Differences were found in the distributions in these two databases, as well as between different samples taken from them. Baseline differences between these two sets of observational data in magnitude, observational techniques and other parameters demonstrate the selection effect in the distribution of meteoric substance. Based on a visual analysis, we conclude that we cannot rule out the possibility of the concentration of the radiants of MARS hyperbolas relative to apexes of the Sun motion in Equatorial/Galactic coordinate systems. The coordinates of the apexes of Sun's motion are determined: for the point with respect to the nearest stars in Hercules constellation as (270,30)/(56,23) degrees; and for the point with respect to the Galactic center in Cygnus as (318,48)/(0,90) degrees.

Spectral, Photometric, and Dynamic Analysis of Eight Draconid Meteors

We analyzed spectra, trajectories, orbits, light curves, and decelerations of eight Draconid meteors observed from Northern Italy on October 8, 2011. Meteor morphologies of two of the meteors are also presented, one of them obtained with a high resolution camera. Meteor radiants agree with theoretical predictions, with a hint that some meteors may belong to the pre-1900 meteoroid trails. The spectra confirm that Draconids have normal chondritic composition of main elements (Mg, Fe, Na). There are, nevertheless, differences in the temporal evolution of Na line emission. The differences are correlated with the shapes of the light curves and the deceleration rates. Our data confirm that Draconids are porous conglomerates of grains, nevertheless, significant differences in the atmospheric fragmentation of cm-sized Draconids were found. Various textures with various resistance to fragmentation exist among Draconid meteoroids and even within single meteoroids.

First results from the 2009-2010 MU radar head echo observation programme for sporadic and shower meteors: the Orionids 2009

The aim of this paper is to demonstrate the capabilities of a new automated analysis scheme developed for meteor head echo observations by the Shigaraki middle and upper atmosphere (MU) radar in Japan (N, E). Our analysis procedure computes meteoroid range, velocity and deceleration as functions of time with unprecedented accuracy and precision. This is crucial for estimations of meteoroid mass and orbital parameters, as well as investigations into meteoroid–atmosphere interaction processes. We collected an extensive set of data (>500 h) between 2009 June and 2010 December. Here, we present initial results from data taken in 2009 October 19–21. More than 600 of about 10 000 head echoes recorded during 33 h were associated with the 1P/Halley dust of the Orionid meteor shower. These meteors constitute a very clear enhancement of meteor radiants centred around right ascension α= and declination δ=. Their estimated atmospheric entry velocity of 66.9 km s−1 is in good agreement with 1P/Halley dust ejected in the year 1266 bc, which, according to simulations, crossed Earth’s orbit at the time of our observation. The Orionid activity within the MU radar beam reached about 50 h−1 during radiant culmination. The flux of sporadic meteors in the MU radar data, coming primarily from the direction of the Earth’s apex, peaked at about 700 h−1 during the same observations.

High resolution radiant distribution and orbits of sporadic radar meteoroids

Five years of meteor orbit data from CMOR (the Canadian Meteor Orbit Radar) are used to study the high-resolution orbital structure of the sporadic meteoroid complex. The large number of high quality orbits (2.35 million) allows the orbital characteristics of meteoroids to be studied not only in the five sporadic sources accessible from the latitude of London, Ontario, Canada, but at a resolution of 2 degrees. The radiant distribution of sporadic meteors is investigated, applying corrections for observing biases, and weighting to a constant limiting mass, and to a constant limiting energy. The orbital distribution of the sporadic sources is compared to other studies. The variation of average geocentric speed, semimajor axis, eccentricity, inclination and perihelion distance with meteoroid radiant is investigated. The source of a ring depleted in meteor radiants at 55 degrees from the apex is attributed to shorter collisional lifetimes inside the ring, due to a higher probability of catastrophic collisions with particles in the zodiacal cloud for the predominantly retrograde meteoroids inside the ring.

Radiants of the Leonids 1999 and 2001 Obtained by Lltv Systems Using Automatic Software Tools

Both amateur and professional meteor groups are more frequently using Low-Light level TV (LLTV) systems to record meteors. Double-station observations can yield orbit data. However, data analysis normally is still done by hand and thus time consuming. This paper addresses the question of whether available automated tools can be used to determine reasonably accurate orbits with minimum human intervention. The European Space Agency performed several observing campaigns to observe the Leonid meteor stream. In November 1999, the ESA meteor group was stationed at two locations in Southern Spain, in November 2001 at two stations close to Broome in North-Western Australia. Double-station observations with LLTV systems were conducted. The data was recorded on S-VHS video tapes. The tapes were processed using automatic detection software from which meteor heights, velocities and radiants were computed. This paper shows the results for the two maximum nights. The radiants determined in 1999 show a very large scatter due to unfortunate observing geometry and inaccurate position determination since one of the cameras was moving because of the wind. The 2001 data is excellent and the radiant was determined to be at RA = 153.96°±0.3° and Dec = 21.09°±0.2°. The error bars for individual meteor radiants are about 0.2° to 0.4°. This demonstrates that is indeed possible to determine good radiant positions using totally automated tools. Orbits, on the other hand, are not well defined due to the fact that the velocity of individual meteors shows large errors. Reasons for this are described.

Diurnal and annual variations of meteor rates at the arctic circle

Abstract. Meteors are an important source for (a) the metal atoms of the upper atmosphere metal layers and (b) for condensation nuclei, the existence of which are a prerequisite for the formation of noctilucent cloud particles in the polar mesopause region. For a better understanding of these phenomena, it would be helpful to know accurately the annual and diurnal variations of meteor rates. So far, these rates have been little studied at polar latitudes. Therefore we have used the 33 MHz meteor radar of the ALOMAR observatory at 69° N to measure the meteor rates at this location for two full annual cycles. This site, being within 3° of the Arctic circle, offers in addition an interesting capability: The axis of its antenna field points (almost) towards the North ecliptic pole once each day of the year. In this particular viewing direction, the radar monitors the meteoroid influx from (almost) the entire ecliptic Northern hemisphere. We report on the observed diurnal variations (averaged over one month) of meteor rates and their significant alterations throughout the year. The ratio of maximum over minimum meteor rates throughout one diurnal cycle is in January and February about 5, from April through December 2.3±0.3. If compared with similar measurements at mid-latitudes, our expectation, that the amplitude of the diurnal variation is to decrease towards the North pole, is not really borne out. Observations with the antenna axis pointing towards the North ecliptic pole showed that the rate of deposition of meteoric dust is substantially larger during the Arctic NLC season than the annual mean deposition rate. The daylight meteor showers of the Arietids, Zeta Perseids, and Beta Taurids supposedly contribute considerably to the June maximum of meteor rates. We note, though, that with the radar antenna pointing as described above, all three meteor radiants are close to the local horizon but all three radiants were detected.

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.

The D Discriminant and Near-Earth Asteroid Streams

A method of separating an association of orbits, a stream, from the local background using the traditional D discriminant is introduced. Applying this procedure to all 708 asteroids with perihelia less than 1.3 AU known on April 22, 1999 suggests that the orbits of Earth-approaching asteroids may be rather organized. By searching the volume around every orbit in the sample space, 14 associations are found with from 4 to 25 members that statistically stand out from the local background. A more traditional search, where orbits are gathered into strings with every orbit connected to at least one other orbit by D< D c , reveals eight additional three-member strings. Using Poisson statistics seven pairs are identified as having exceptionally similar orbits; three of these pairs are a part of an association or string. On the other hand, comparing the results of a volume search around randomized orbits indicates that perhaps 50 to 75% of these groupings are due to chance, indicating that observational effects may severely affect the background and therefore the reality of the associations that are separated out. The lack of compositional or taxonomic information about most of the 155 asteroids, 22% of the sample, hinders interpretation of the nature of the streams. Of the three associations found in an earlier study (Drummond 1991, Icarus 89, 14–25), only one remains intact as a result of the stricter statistical requirements adopted here. Three of four fireball streams (Halliday et al. 1990, Meteoritics 25, 93–99), previously found to be related to the old associations, can be loosely associated with three of the new associations, but none of the four recovered meteorites with known orbits can be associated with them. Nevertheless, theoretical meteor radiants are listed, all of which are so large and diffuse, and have such slow geocentric velocities, that it is doubtful if visual meteor showers can be linked to the new streams. However, these associations, strings, and pairs of asteroids are good candidates for meteorite sources, especially where organized falls are recognized, since they generally satisfy the immediate dynamical requirements for delivery, namely, gentle geocentric velocities produced by overtaking the Earth around sunset.

On the possible relation between the Tunguska bolide and comet Encke

Almost two decades ago Ľ. Kresák ( Bull. Astron. Inst. Czechoslov. 29, 129–134, 1978) suggested that the Tunguska bolide might be a fragment of comet Encke, a hypothesis that Z. Sekanina criticized in a publication a few years later ( Astron. J. 88, 1382–1414, 1983). One aspect of the proposed genetic relationship is investigated, namely the required differential orbital precession of the two objects so as to make an impact upon our planet possible for the Tunguska projectile, even though the comet's orbit in the current epoch is far from the condition of Earth intersection. This work was foreshadowed in a previous paper in which it was shown how theoretical meteor radiants may be calculated for objects with orbits similar to 2P/Encke ( Earth, Moon and Planets 68, 155–164, 1995). By applying appropriate secular perturbation theory and numerical integration techniques, it is shown that the necessary dispersion can be attained within 10 kyr if the semi-major axes of the orbits differ by ∼0.05 AU, an amount easily achieved even under the presently observed non-gravitational forces of 2P/Encke.

Is 2329 Orthos a dead comet?

Probably most meteor showers have a cometary origin. Investigation of Near-Earth asteroids’ orbital evolution to determine whether they have related meteor showers is necessary to determine which asteroids evolved from comets. The results of calculations show that asteroid Orthos’ orbit is an octuple Earth-crosser. Therefore, if Orthos has an old meteoroid stream it may produce eight meteor showers observable on the Earth. The existence of four Orthos’ Northern meteor showers is confirmed by our search in the published catalogues of meteor radiants and orbits or in the archives of the IAU Meteor Data Center (Lund, Sweden).

Orthos' meteor showers

Probably the majority of meteor showers has a cometary origin. Investigation of Near-Earth asteroids' orbital evolution to determine whether they have related meteor showers are necessary to determine which asteroids evolved from comets. The results of calculations show that asteroid Orthos' orbit is an octuple Earth-crosser. Therefore, if Orthos has an old meteoroid stream it may produce eight meteor showers observable on the Earth. The existence of four Orthos' Northern meteor showers is confirmed by our search in the published catalogues of meteor radiants and orbits or in the archives of the IAU Meteor Data Center (Lund, Sweden).

Theoretical meteor radiants for macroscopic Taurid Complex objects

The calculation of theoretical meteor radiants is discussed for comets and asteroids whose orbits pass within, but at present do not necessarily intersect, that of the Earth, in particular from the perspective of developing a suitable method for application to Taurid Complex orbits. The main question addressed here is how to allow for dynamical evolution between epochs when an orbit isnot Earth-intersecting (as at present in most cases for macroscopic bodies) and those when itis (i.e., when meteors can actually be observed). This should be understood in terms of evolution in the past, such that meteoroids released some time ago have evolved differentially from the putative parents, allowing meteors to be detected now. Theoretical radiants for macroscopic Taurid objects are then presented and compared with observations of the nighttime and daytime Taurid meteor showers. These are found to be broadly similar in form, given the sparsity of some of the data, adding weight to the hypothesis that this sub-jovian complex contains kilometre-plus asteroids. A similar conclusion results for the group of objects in similar orbits to (2212) Hephaistos.

The association of Earth-crossing asteroids with meteoroid streams

Various points are discussed concerning the association of Earth-crossing asteroids (ECAs) with meteoroid streams, including the drawbacks of the techniques used in some previous work. In comparing the theoretical radiants of any ECA (or, indeed, comet) with observed meteor radiants it is necessary that the orbit used be that appropriate for epochs when the ECA has a node at 1 AU; in each precession cycle of the argument of perihelion (ω) there will be four values rendering a node at the Earth's orbit, so that four showers are expected. Precession of the node will result in sets of showers at different times of year from differentω-precession cycles, whilst for some objects the orbital evolution is more convoluted. For diffuse, low-flux showers a problem is differentiating the meteors associated with any ECA from the sporadic background; a new graphical technique is introduced for illuminating whether such associations exist. A re-evaluation is required of whether ECAs should be thought of as being parent bodies of specific showers. Although this might be the case for some very large ECAs (such as (3200) Phaethon, associated with the Geminid stream), the bodies observed now being extinct or dormant cometary cores, it is suggested that in general the ECAs are better thought of as being large fragments produced in hierarchical cometary disintegrations. That is, some ECAs are just the largest meteoroids in meteoroid streams.

Applicability of meteor radiant determination methods depending on orbit type

It is evident that there is no uniform method of calculating meteor radiants which would yield reliable resilts for all types of cometary orbits. In the present paper an analysis of this problem is presented, together with recommended methods for various types of orbits. Some additional methods resulting from mathematical modelling are presented and discussed together with Porter's, Steel-Baggaley's and Hasegawa's methods. In order to be able to compare how suitable the application of the individual radiant determination methods is, it is necessary to determine the accuracy with which they approximate real meteor orbits. To verify the accuracy with which the orbit of a meteoroid with at least one node at 1 AU fits the orignal orbit of the parent body, we applied the Southworth-Hawkins D-criterion (Southworth and Hawkins, Smithson Contr. Astrophys. 7, 261, 1963). D ⩽ 0.1 indicates a very good fit of orbits, 0.1 < D ⩽ 0.2 is considered to be a good fit of orbits, and D > 0.2 the fit is rather poor and the change of orbit unrealistic. The optimal methods with the smallest values of D for given types of orbits anre shown in three plots. The new mathod of retation around the line of apsides we propose is very appropriate is the region of small inclinations Hasegawa's ω-adjustment method ( Publ. Astrpn. Soc. Jpn 42, 175, 1990) has the widest application.

Meteoroid Streams

Meteoroid streams, producing meteor showers if some part of the stream has a node near 1 AU, have complex structures which are only just beginning to be understood. The old simplistic idea of a narrow loop being formed about the orbit of a parent comet with one, or possibly two, terrestrial intersection(s) is now being replaced by the recognition that their dynamical evolution may render convoluted and distorted ribbon shapes with eight or more distinct showers being generated. As such the streams are excellent tracers of the sorts of orbital evolution which may be undergone by larger objects (asteroids and comets) in the inner solar system; indeed it is now known that objects presently observed as Apollo-type asteroids may also be the progenitors of streams.Searches for showers associated with newly-discovered possible parent objects may be carried out either via the calculation of theoretical meteor radiants (which have hitherto been derived using an untenable method), or through searches of catalogues of individual meteor orbits. In order to accomplish the latter, about 68,000 radar, photographic and TV meteor orbits from various programmes in the U.S.A., the former Soviet Union, Canada and Australia are available from the IAU Meteor Data Center, and more than 350,000 orbits of very faint meteors have been determined over the past three years using a new facility in New Zealand.The discovery amongst IRAS data of dust trails lagging behind comets has opened up a new way in which meteoroid streams may be investigated, although the relationship between these trails and the streams observed as meteor showers at the Earth is by no means clear at this stage. Similarly radar, radio and spacecraft impact observations of meteoroids near cometary nuclei have added to our knowledge.In spite of the improvement in our understanding of meteoroid streams over the past few years it is clear that there is much still to be done. The words of W.F. Denning in 1923 are still pertinent: “Few astronomers occupy themselves with the observation and investigation of meteors, and yet it is an attractive field of work offering inviting prospects of new discoveries”.

Comparison of predicted and measured detection rates of meteor signals

Comparisons of monthly‐averaged daily cycles of measured and predicted detection rates of meteor signals for a midpath and an endpath meteor link are used to reveal the validity and limitations of published radiant distributions of meteors. A new method is used to aid in determining the validity and limitations of the nonuniform distributions. Discrepancies in the published, predicted, and measured annual variations in the detection rate of meteor signals are investigated. Contrary to recently published information, predicted annual variations in the detection rate of meteor signals that are caused by meteor radiants close to the ecliptic are shown to be comparable to measured results.

Theoretical meteor radiants of Apollo, Amor, and Aten asteroids

Abstract A compilation of theoretical meteor radiants is presented for all numbered (through 2525) asteroids which approach the Earth's orbit to within 0.20 AU. On the basis of orbital similarity, asteroids associated with current meteor streams and Prairie Network fireballs are listed; plausible associations with medieval fireball radiants are also given. The best defunct comet candidates in terms of meteoric evidence appear to be 2101 Adonis and 2201 1947XC. Asteroids which may be either extinct comets or perturbed main belt asteroids accompanied by collisional debris (represented by fireballs) are 1917 Cuyo, 2202 Pele, 2061 Anza, and 2340 Hathor. 1566 Icarus and 1981 Midas are the only asteroids whose orbits approach to less than 0.07 AU of the Earth's orbit, have a northern radiant, and still show no certain meteoric activity. The majority of Atens, Apollos, and Amors do not pass sufficiently close (