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1.
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
2.
Efforts to link minor meteor showers to their parent bodies have been hampered both by the lack of high-accuracy orbits for
weak showers and the incompleteness of our sample of potential parent bodies. The Canadian Meteor Orbital Radar (CMOR) has
accumulated over one million meteor orbits. From this large data set, the existence of weak showers and the accuracy of the
mean orbits of these showers can be improved. The ever-growing catalogue of near-Earth asteroids (NEAs) provides the complimentary
data set for the linking procedure. By combining a detailed examination of the background of sporadic meteors near the orbit
in question (which the radar data makes possible) and by computing the statistical significance of any shower association
(which the improved NEA sample allows) any proposed shower–parent link can be tested much more thoroughly than in the past.
Additional evidence for the links is provided by a single-station meteor radar at the CMOR site which can be used to dispel
confusion between very weak showers and statistical fluctuations in the sporadic background. The use of these techniques and
data sets in concert will allow us to confidently link some weak streams to their parent bodies on a statistical basis, while
at the same time showing that previously identified minor showers have little or no activity and that some previously suggested
linkages may simply be chance alignments. 相似文献
3.
M. Hajduková Jr. 《Earth, Moon, and Planets》2008,102(1-4):67-71
The hyperbolic meteor orbits among the 4,581 photographic and 62,906 radar meteors of the IAU MDC have been analysed using
statistical methods. It was shown that the vast majority of hyperbolic orbits has been caused by the dispersion of determined
velocities. The large proportion of hyperbolic orbits among the known meteor showers strongly suggests the hyperbolicity of
the meteors is not real. The number of apparent hyperbolic orbits increases inversely proportional to the difference between
the mean heliocentric velocity of meteor shower and the parabolic velocity limit. The number of hyperbolic meteors in the
investigated catalogues does not, in any case, represent the number of interstellar meteors in observational data. The apparent
hyperbolicity of these orbits is caused by a high spread in velocity determination, shifting a part of the data through the
parabolic limit. 相似文献
4.
David D. Meisel Johan Kero Csilla Szasz Vladimir Sidorov Stan Briczinski 《Earth, Moon, and Planets》2008,102(1-4):315-322
In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number
of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of
true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single
beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with
simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity
as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position
and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been
kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from
the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative
scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source
areas where it is easiest to detect discrete showers with less confusion from the background. 相似文献
5.
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
6.
We tested four criteria used for discrimination between asteroidal and cometary type of orbits: Whipple criterion K, Kresak
criterion Pe, Tisserand invariant T and aphelion distance Q. To estimate their reliability, all criteria were applied to classify
the 2225 orbits of NEAs and 582 orbits of comets, for several epochs spanning the time interval of 40 thousands years. The
Q-criterion produced the smallest number of exceptions and has shown the best stability. The biggest number of exceptions
and the biggest variations are obtained for the K-criterion. We applied the Q-criterion to classify meteor orbits from the
IAU Meteor Data Center and the video meteor orbits available on the Web sites. Among the sporadic radar orbits, as well as
among the mean orbits of meteor streams a strong preponderance of asteroid-type orbits was observed. In case of the photographic
and video meteors a weak preponderance of cometary and asteroidal orbits was found, respectively. 相似文献
7.
W. G. Elford 《Earth, Moon, and Planets》1995,71(3):245-253
Particles of mass less than about 1 gm are a minor fraction of the total matter impinging on the Earth averaged over millennia time scales. However, these particles dominate during a single particular year and produce the most obvious evidence of incoming extra-terrestrial matter in the form of ablation trails in the atmosphere which are visible at night as meteors.Observations of meteors give astronomical information on the composition, structure, and cometary associations of the particles. The composition is deduced from optical spectra of meteors, whilst telescopic studies of the trails during formation give information on the physical structure of the particles. Any cometary associations are deduced from measurement of meteor orbits determined photographically, using television, or by radar.Meteors occur in the atmosphere at heights from about 70 to 120 km. Optical observations are restricted to night-time and usually under conditions of low moonlight. A typical television based detector can record +8M meteors with a sporadic rate of 15–20 per hour and velocities accurate to about 3%. The luminosity of the trail is strongly dependent on the velocity of the meteoroid (to about the third power).Radar observations of meteors are unrestricted by weather or time of day, and can readily detect meteors at least two orders of magnitude smaller in mass than those detectable optically. Again the observations are heavily biased toward the higher velocities as the electron line density varies approximately asV
3.5. However, the higher the velocity of the meteoroid the greater the height of the meteor trail, and the reduced probability of radar detection due to rapid diffusion of the trail. Thus radar observations tend to select meteors in the intermediate velocity range 30–40 km s–1. 相似文献
8.
C. Szasz J. Kero D. D. Meisel A. Pellinen-Wannberg G. Wannberg A. Westman 《Monthly notices of the Royal Astronomical Society》2008,388(1):15-25
The tristatic EISCAT 930-MHz UHF system is used to determine the absolute geocentric velocities of meteors detected with all three receivers simultaneously at 96 km, the height of the common radar volume. The data used in this study were taken between 2002 and 2005, during four 24-h runs at summer/winter solstice and vernal/autumnal equinox to observe the largest seasonal difference. The observed velocities of 410 tristatic meteors are integrated back through the Earth atmosphere to find their atmospheric entry velocities using an ablation model. Orbit calculations are performed by taking zenith attraction, Earth rotation as well as obliquity of the ecliptic into account. The results are presented in the form of different orbital characteristics. None of the observed meteors appears to be of extrasolar or asteroidal origin; comets, particularly short-period (<200 yr) ones, may be the dominant source for the particles observed. About 40 per cent of the radiants can be associated with the north apex sporadic meteor source and 58 per cent of the orbits are retrograde. There is evidence of resonance gaps at semimajor axis values corresponding to commensurabilities with Jupiter, which may be the first convincing evidence of Jupiter's gravitational influence on the population of small sporadic meteoroids surveyed by radar. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km s−1 and a retrograde population peaking at 59 km s−1 . The EISCAT radar system is located close to the Arctic Circle, which means that the North Ecliptic Pole (NEP) is near zenith once every 24 h, i.e. during each observational period. In this particular geometry, the local horizon coincides with the ecliptic plane. The meteoroid influx should therefore be directly comparable throughout the year. 相似文献
9.
P.B. Babadzhanov 《Celestial Mechanics and Dynamical Astronomy》1997,69(1-2):221-234
Recent theoretical and observational work has shown that the asteroids belonging to the Taurid meteoroid complex have a cometary
nature. If so, then they might possess related meteoroid streams producing meteor showers in the Earth atmosphere. We studied
the orbital evolution of ten numbered Taurid complex asteroids by the Halphen-Goryachev method. It turned out that all of
these asteroids are quadruple crossers relative to the Earth's orbit. Therefore their proposed meteoroid streams may in theory
each produce four meteor showers. The theoretical orbital elements and geocentric radiants of these showers are determined
and compared with the available observational data. The existence of the predicted forty meteor showers of the ten Taurid
complex asteroids is confirmed by a search of the published catalogues of observed meteor shower radiants and orbits, and
of the archives of the IAU Meteor Data Center (Lund). The existence of meteor showers associated with the Taurid Complex Asteroids
confirms that, most likely, these asteroids are extinct comets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
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
12.
In order to assess the possibility of meteoroid streams detectable from the surface of Mars as meteor showers we have derived minimum distances and associated velocities for a large sample of small body orbits relative to the orbits of Mars and the Earth. The population ratio for objects approaching to within 0.2 AU of these two planets is found to be approximately 2:1. The smaller relative velocities in the case of Mars appears to be the main impediment to the detection of meteors in the upper atmosphere of that planet. We identify five bodies, including the unusual object (5335) Damocles and periodic comet 1P/Halley, with relative orbital parameters most suitable to produce prominent meteor showers. We identify specific epochs at which showers related to these bodies are expected to occur. An overview of possible detection methods taking into account the unique characteristics of the Martian environment is presented. We pay particular attention on the effects of such streams on the dust rings believed to be present around Mars. 相似文献
13.
P. Jenniskens P.S. Gural L. Dynneson B.J. Grigsby K.E. Newman M. Borden M. Koop D. Holman 《Icarus》2011,216(1):40-61
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. 相似文献
14.
P. B. Babadzhanov 《Earth, Moon, and Planets》1995,68(1-3):165-170
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). 相似文献
15.
P. B. Babadzhanov 《Earth, Moon, and Planets》1995,71(3):305-310
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). 相似文献
16.
P. B. Babadzhanov 《Earth, Moon, and Planets》1996,72(1-3):305-310
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). 相似文献
17.
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. 相似文献
18.
Meteoroids that orbit the Sun encounter the Earth with speeds between 11 and 74 km/sec. However, the distribution of the velocities of meteoroids between these limits is not well known. The uncertainty is caused by the difficulty in measuring the true flux of meteors at the extrema of the velocity distribution. Whilst the most comprehensive measurements of meteor flux are those obtained using radio techniques, meteors with speeds > 50 km/sec occur at heights where the effects of initial radius of the trail and diffusion significantly reduce the radio reflection from the trails; on the other hand the high dependence of the collisional ionization probability on velocity (to the power 3.5) significantly inhibits the detection of meteors with speeds < 20 km/sec. Recent developments in meteor radar systems are now making it possible to measure the velocity of meteors at the extrema of the distribution. For meteoroids ablating at heights between 100 and 120 km the speed of entry can be measured at 2 and 6 MHz using a radar with a 1 km diameter array located near Adelaide; these observations will commence early in 1995. In the meantime a 54 MHz MST radar is being operated at a pulse repetition frequency of 1024 Hz to search for the presence of interstellar (speed > 74 km/sec) meteors. Both these radars exploit the phase information available prior to the closest-approach (to) point. 相似文献
19.
Apostolos A Christou 《Icarus》2004,168(1):23-33
We investigate the possibility of detectable meteor shower activity in the atmosphere of Venus. We compare the Venus-approaching population of known periodic comets, suspected cometary asteroids and meteor streams with that of the Earth. We find that a similar number of Halley-type comets but a substantially lesser population of Jupiter family comets approach Venus. Parent bodies of prominent meteor showers that might occur at Venus have been determined based on minimum orbital distance. These are: Comets 1P/Halley, parent of the η Aquarid and Orionid streams at the Earth; 45P/Honda-Mrkos-Pajdusakova which currently approaches the venusian orbit to 0.0016 AU; three Halley-type comets (12P/Pons-Brooks, 27P/Crommelin and 122P/de Vico), all intercepting the planet's orbit within a 5-day arc in solar longitude; and Asteroid (3200) Phaethon, parent of the December Geminids at the Earth. In addition, several minor streams and a number of cometary asteroid orbits are found to approach the orbit of Venus sufficiently close to raise the possibility of some activity at that planet. Using an analytical approach described in Adolfsson et al. (Icarus 119 (1996) 144) we show that venusian meteors would be as bright or up to 2 magnitudes brighter than their Earth counterparts and reach maximum luminosity at an altitude range of 100-120, 20-30 km higher than at the Earth, in a predominantly clear region of the atmosphere. We discuss the feasibility of observing venusian showers based on current capabilities and conclude that a downward-looking Venus-orbiting meteor detector would be more suitable for these purposes than Earth-based monitoring. The former would detect a shower of an equivalent Zenithal Hourly Rate of at least several tens of meteors. 相似文献
20.
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