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1.
Using a meteor orbit radar, a total of more than 2.5 million meteoroids with masses ∼10−7 kg have had orbits measured in the interval 2002-2006. From these data, a total of 45 meteoroid streams have been identified using a wavelet transform approach to isolate enhancements in radiant density in geocentric coordinates. Of the recorded streams, 12 are previously unreported or unrecognized. The survey finds >90% of all meteoroids at this size range are part of the sporadic meteoroid background. A large fraction of the radar detected streams have q<0.15 AU suggestive of a strong contribution from sungrazing comets to the meteoroid stream population currently intersecting the Earth. We find a remarkably long period of activity for the Taurid shower (almost half the year as a clearly definable radiant) and several streams notable for a high proportion of small meteoroids only, among these a strong new shower in January at the time of the Quadrantids (January Leonids). A new shower (Epsilon Perseids) has also been identified with orbital elements almost identical to Comet 96P/Machholz. 相似文献
2.
Devulapalli Venkata Phani Kumar Kammadhanam Chenna Reddy Ganji Yellaiah 《Astrophysics and Space Science》2006,306(4):235-239
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. 相似文献
3.
V. Sidorov S. Kalabanov S. Sidorova I. Filin T. Filimonova 《Earth, Moon, and Planets》2004,95(1-4):165-179
The discrete quasitomographic method of the analysis of the interferometric data of meteor radar gives us the possibility
of measuring coordinates and velocities of very weak meteor showers with a 2 × 2 square degree resolution on the celestial
sphere. The minimal rate of the meteors in each microstream is five meteors per day. At such sensitivity, basic distinctions
between irregularities of the sporadic background and meteor streams vanish. More than 1000 of the detected microshowers per
month are associated with a combination of (a) the large known meteor showers, (b) the weaker known meteor showers and (c)
till now unknown associations of microshowers. All microshowers regardless of association have the identical velocities, limited
areas of radiation and near simultaneity of their acting dates. The results are compiled as maps of radiant distribution and
average velocities of microstreams for different months. From these it is possible to see how the microshower activity for
various discrete sites on the celestial sphere correlate with the behavior of the well-known meteor streams and thus to infer
the orbital properties of the different microstream configurations. 相似文献
4.
A 7 year survey using the Canadian Meteor Orbit Radar (CMOR), a specular backscattering orbital radar, has produced three million individually measured meteoroid orbits for particles with mean mass near 10−7 kg. We apply a 3D wavelet transform to our measured velocity vectors, partitioning them into 1° solar longitude bins while stacking all 7 years of data into a single “virtual” year to search for showers which show annual activity and last for at least 3 days. Our automated stream search algorithm has identified 117 meteor showers. We have recovered 42 of the 45 previously described streams from our first reconnaissance survey (Brown, P., Weryk, R.J., Wong, D.K., Jones, J. [2008]. Icarus 195, 317-339). Removing possible duplicate showers from the automated results leaves 109 total streams. These include 42 identified in survey I and at least 62 newly identified streams. Our large data sample and the enhanced sensitivity of the 3D wavelet search compared to our earlier survey have allowed us to extend the period of activity for several major showers. This includes detection of the Geminid shower from early November to late December and the Quadrantids from early November to mid-January. Among our newly identified streams are the Theta Serpentids which appears to be derived from 2008 KP and the Canum Venaticids which have a similar orbit to C/1975 X1 (Sato). We also find evidence that nearly 60% of all our streams are part of seven major stream complexes, linked via secular invariants. 相似文献
5.
High-power, large-aperture (HPLA) radars detect the plasma that forms in the vicinity of a meteoroid and moves approximately at its velocity; reflections from these plasmas are called head echoes. For over a decade, HPLA radars have been detecting head echoes with peak velocity distributions >50 km/s. These results have created some controversy within the field of meteor physics because previous data, including spacecraft impact cratering studies, optical and specular meteor data, indicate that the peak of the velocity distribution to a set limiting mass should be <20 km/s [Love, S.G., Brownlee, D.E., 1993. Science 262, 550-553]. Thus the question of whether HPLA radars are preferentially detecting high-velocity meteors arises. In this paper we attempt to address this question by examining both modeled and measured head echo data using the ALTAIR radar, collected during the Leonid 1998 and 1999 showers. These data comprise meteors originating primarily from the North Apex sporadic meteor source. First, we use our scattering theory to convert measured radar-cross-section (RCS) to electron line density and mass, as well as to convert modeled electron line density and mass to RCS. We subsequently compare the dependence between mass, velocity, mean-free-path, RCS and line density using both the measured and modeled data by performing a multiple, linear regression fit. We find a strong correlation between derived mass and velocity and show that line density is approximately proportional to mass times velocity3.1. Next, we determine the cumulative mass index using subsets of our data and use this mass index, along with the results of our regression fit, to weight the velocity distribution. Our results show that while there does indeed exist a bias in the measured head echo velocity distribution, it is smaller than those calculated using traditional specular trail data due to the different scattering mechanism, and also includes a bias against the low-mass, very high-velocity meteoroids. 相似文献
6.
J. P. Younger I. M. Reid R. A. Vincent D. A. Holdsworth D. J. Murphy 《Monthly notices of the Royal Astronomical Society》2009,398(1):350-356
The 33.2 MHz interferometric meteor radars located at Davis Station, Antarctica and Darwin, Australia typically detect around 15 000 specular underdense meteor echoes every day. While the angle of arrival of the scattered radio wave can be inferred using phase differences between receive antennae, the direction of individual meteors is not known beyond a plane of ambiguity perpendicular to the angle of arrival. Using the great circle mapping technique with a Jones & Jones type weighting function, 37 meteor shower systems were detected in data collected at both locations over 2006–2007, including nine undocumented showers. The orbital elements of the parent debris streams were then calculated for the 31 showers where sufficiently precise measurements were available. 相似文献
7.
Radio meteor observations by Ham-band beacon or FM radio broadcasts using “Ham-band Radio meteor Observation Fast Fourier
Transform” (HROFFT) an automatic operating software have been performed widely in recent days. Previously, counting of meteor
echoes on the spectrograms of radio meteor observation was performed manually by observers. In the present paper, we introduce
an automatic meteor echo counting software application. Although output images of the HROFFT contain both the features of
meteor echoes and those of various types of noises, a newly developed image processing technique has been applied, resulting
in software that enables a useful auto-counting tool. There exists a slight error in the processing on spectrograms when the
observation site is affected by many disturbing noises. Nevertheless, comparison between software and manual counting revealed
an agreement of almost 90%. Therefore, we can easily obtain a dataset of detection time, duration time, signal strength, and
Doppler shift of each meteor echo from the HROFFT spectrograms. Using this software, statistical analyses of meteor activities
is based on the results obtained at many Ham-band Radio meteor Observation (HRO) sites throughout the world, resulting in
a very useful “standard” for monitoring meteor stream activities in real time. 相似文献
8.
D. J. Asher 《Earth, Moon, and Planets》2008,102(1-4):27-33
The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on
the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical
evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust
trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time
through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily
determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once
an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with
observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from
the nucleus, including the mass distribution of ejected meteoroids. 相似文献
9.
We deal with theoretical meteoroid streams the parent bodies of which are two Halley-type comets in orbits situated at a relatively
large distance from the orbit of Earth: 126P/1996 P1 and 161P/2004 V2. For two perihelion passages of each comet in the far
past, we model the theoretical stream and follow its dynamical evolution until the present. We predict the characteristics
of potential meteor showers according to the dynamical properties of theoretical particles currently approaching the orbit
of the Earth. Our dynamical study reveals that the comet 161P/2004 V2 could have an associated Earth-observable meteor shower,
although no significant number of theoretical particles are identified with real, photographic, video, or radar meteors. However,
the mean radiant of the shower is predicted on the southern sky (its declination is about −23°) where a relatively low number
of real meteors has been detected and, therefore, recorded in the databases used. The shower of 161P has a compact radiant
area and a relatively large geocentric velocity of ∼53 km s−1. A significant fraction of particles assumed to be released from comet 126P also cross the Earth’s orbit and, eventually,
could be observed as meteors. However, their radiant area is largely dispersed (declination of radiants spans from about +60°
to the south pole) and, therefore, mixed with the sporadic meteor background. An identification with real meteors is practically
impossible. 相似文献
10.
Ohtsuka Katsuhito Shimoda Chikara Yoshikawa Makoto Watanabe Jun-Ichi 《Earth, Moon, and Planets》1997,77(2):83-91
The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear.
Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile
of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude
(J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of
2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type
asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids :
Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon,
we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams
are really associated with Phaethon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Josep M. Trigo-Rodriguez José M. Madiedo Peter S. Gural Alberto J. Castro-Tirado Jordi Llorca Juan Fabregat Standa Vítek Pep Pujols 《Earth, Moon, and Planets》2008,102(1-4):231-240
By using high-resolution, low-scan-rate, all-sky CCD cameras, the SPanish Meteor Network (SPMN) is currently monitoring meteor
and fireball activity on a year round basis. Here are presented just a sampling of the accurate trajectory, radiant and orbital
data obtained for meteors imaged simultaneously from two SPMN stations during the continuous 2006–2007 coverage of meteor
and fireball monitoring. Typical astrometric uncertainty is 1–2 arc min, while velocity determination errors are of the order
of 0.1–0.5 km/s, which is dependent on the distance of each event to the station and its particular viewing geometry. The
cameras have demonstrated excellent performance for detecting meteor outbursts. The recent development of automatic detection
software is also providing real-time information on the global meteor activity. Finally, some examples of the all-sky CCD
cameras applications for detecting unexpected meteor activity are given. 相似文献
12.
Meteor radar observations of ionized trails in the Earth’s atmosphere provide observations that do not depend on weather conditions
and time of day and provide good statistics for analysis. Further development in the new quasitomographic analysis of the
goniometric data of the Kazan meteoric radar has revealed a number of very weak meteoric streams with rates of more than 5–6
meteors per day. In addition to the known large meteor showers, we have found up to as many as 1000 small showers per month
that we have named microshowers. We shall operationally define a microshower as the minimal meteoric stream which can be detected
with the Kazan meteoric radar while quasitomographic procedures of processing interferometer data are used. 相似文献
13.
V. A. Leonov 《Solar System Research》2010,44(2):122-135
Massive television observations of meteors aimed at verifying the existing and finding new meteor streams create the task
of the reliable preliminary determination of the detected meteor membership in a particular known stream. The mostly widely
used method of meteor identification is connected with the estimation of the distance between the great circle of the meteor
and the point of the examined radiant. Often observers perform this estimation without checking the possibility that the same
meteor belongs to another stream. When several streams occur simultaneously, many meteors can be members of two or more streams.
When the determination of the meteor membership is done in a subjective way, it may lead to an overestimation of strong streams’
and an underestimation of weak streams’ activity. In this work, we describe a method and algorithm for the determination of
the meteor membership in known streams which were tested using real television observations and were successfully used at
INASAN. This algorithm is almost completely automatic and allows for the obtainment of additional information regarding meteor
streams. We also show some results of the processing of 2254 meteors observations obtained with the FAVOR camera from July
31, 2006 to October 21, 2006 using the proposed method. The work is part of the program for the creation of the Verified Catalogue
of Meteor Streams. 相似文献
14.
Damir Šegon Željko Andreić Peter S. Gural Korado Korlević Denis Vida Filip Novoselnik Ivica Skokić 《Earth, Moon, and Planets》2014,112(1-4):33-44
The predicted Draconid meteor shower outburst during October 2011 had been observed by a portion of the Croatian Meteor Network whose stations encountered clear weather. A total of 95 Draconid orbits have been calculated from 18 contributing stations, and in this paper we present results for 63 orbits obtained from the fully automatic observation and processing pipeline. Two methods of trajectory estimation were applied, showing better fit results using a linearly changing velocity model versus a constant velocity model. The estimated mean radiant position has been found to be at RA = 262.6°, Dec = +55.7°, with estimated geocentric velocity Vg = 20.7 km/s. 相似文献
15.
Glenn Sugar Althea Moorhead Peter Brown William Cooke 《Meteoritics & planetary science》2017,52(6):1048-1059
We present a new method to detect meteor showers using the density‐based spatial clustering of applications with noise algorithm (DBSCAN; Ester et al. 1996 ). The DBSCAN algorithm is a modern cluster detection algorithm that is well suited to the problem of extracting meteor showers from all‐sky camera data because of its ability to efficiently extract clusters of different shapes and sizes from large data sets. We apply this shower detection algorithm on a data set that contains 25,885 meteor trajectories and orbits obtained from the NASA All‐Sky Fireball Network and the Southern Ontario Meteor Network (SOMN). Using a distance metric based on solar longitude, geocentric velocity, and Sun‐centered ecliptic radiant, we find 25 strong cluster detections and six weak detections in the data, all of which are good matches to known showers. We include measurement errors in our analysis to quantify the reliability of cluster occurrence and the probability that each meteor belongs to a given cluster. We validate our method through false‐positive/negative analysis and with a comparison to an established shower detection algorithm. 相似文献
16.
D. A. Mendis 《Astrophysics and Space Science》1973,20(1):165-176
The genetic relationship between short-period comets and meteor streams is investigated. It is shown that mechanisms exist for the radial and the longitudinal focussing of particles in meteor streams with characteristic time scales of agglomeration significantly smaller than those of any of the known dispersive processes. Consequently, it is claimed that meteor streams may not merely form a sink for short-period comets but may also form a source. A likely origin for the volatiles observed in such comets is suggested. It is finally stressed that this reciprocity in the genetic relationship between short-period comets and meteor streams should form an important consideration in any attempt at accounting for the observed population of short-period comets. 相似文献
17.
Jun-ichi Watanabe 《Earth, Moon, and Planets》2004,95(1-4):49-61
Recent progress on the interrelation between meteor streams and comets is reviewed both on dynamical and physical aspects.
The topics include the recent concept of the structure of meteor streams, resulted success of the prediction of the meteor
storms, and the recent observational situation on the cometary dust grains and meteoroids. Two possible explanations for the
origin of the meteoroids together with the implication for the relation between the birthplace of the parent comets and the
meteoroids are discussed. 相似文献
18.
We have carried out double-station TV meteor observations between 1990 and 1994. The orbits of 326 meteors have been determined from doubly observed meteors, and radiant distributions are studied. The mean magnitude of the observed meteors was as faint as +4.7, since I.I. (Image Intensifier) and Video cameras were used. Radiants were widely distributed over the celestial sphere. The velocity distribution showed some similarity with the distribution predicted by the theoretical radiant distribution from comets rather than that from asteroids. In all 13 showers including both major and minor meteor showers were detected from radiant distributions of the observed meteors; from the orbital elements and meteor velocities as well as from the radiant directions. 相似文献
19.
The issue of the presence of meter- and decameter-sized bodies in meteor and fireball streams is of fundamental importance in the context of the theory of disintegration of parent bodies. Our observations, which have been carried out since 1995, indicate that such bodies are present in the Perseid, α-Capricornid, Leonid, and Coma-Berenicid meteoric streams. A catalogue is presented here for the parameters of the detected bodies. The spatial density of the meter-sized bodies is estimated based on the observational material. Within the errors, our estimates agree with the estimates based on the extrapolation of meteor and fireball data. An analysis of the observations suggests some inferences on the structure of the streams under study.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 263–271.Original Russian Text Copyright © 2005 by Barabanov, Smirnov. 相似文献
20.
L. M. G. Poole 《Astrophysics and Space Science》1995,230(1-2):471-478
Recent meteor research in South Africa, arising largely from the development of forward and back scatter observing systems, is briefly reviewed. The main areas of investigation have been the use of single station radars to deduce meteor radiant structures, the study of upper atmospheric wind patterns, and research into the factors which influence the performance of meteor burst communication systems. 相似文献