The orbit and structure of the Lyrid meteor stream based on photographic orbits available in the IAU Meteor database are investigated. Seventeen Lyrids were found in the database and the radiant and orbit of the stream were

derived. In the stream three very distinct groups of orbits—short-period, longperiod and extreme (hyperbolic orbits), are separated. The mutual consistence of the groups is investigated by following the orbital evolution of individual meteors. The long-period group has the evolution almost identical with that of the parent comet C/1861 G1 Thatcher. The hyperbolic orbits are most probably the result of erroneous measurements

Cevolani, G.

Kornoš, L.

Porubčan, V.

English

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NOTE BREVIDOI 10.1393/ncc/i2007-10248-4IL NUOVO CIMENTO Vol. 30 C, N. 4 Luglio-Agosto 2007The orbit, structure and evolution of the Lyrid meteoroid streamV. Porubcˇan(1)(2), L. Kornosˇ(1) and G. Cevolani(3)(1) Department of Astronomy, Physics of the Earth and MeteorologyFMPI Comenius University - 842 48 Bratislava, Slovakia(2) Astronomical Institute of the Slovak Academy of Sciences - 845 04 Bratislava, Slovakia(3) CNR-ISAC - Via Gobetti 101, 40129 Bologna, Italy(ricevuto il 18 Settembre 2007; approvato l’1 Dicembre 2007; pubblicato online il 20 Dicembre2007)Summary. — The orbit and structure of the Lyrid meteor stream based on pho-tographic orbits available in the IAU Meteor database are investigated. SeventeenLyrids were found in the database and the radiant and orbit of the stream werederived. In the stream three very distinct groups of orbits—short-period, long-period and extreme (hyperbolic orbits), are separated. The mutual consistence ofthe groups is investigated by following the orbital evolution of individual meteors.The long-period group has the evolution almost identical with that of the parentcomet C/1861 G1 Thatcher. The hyperbolic orbits are most probably the result oferroneous measurements.PACS 96.30.Za – Meteors, meteorites and tektites.PACS 96.30.Ys – Asteroids, meteoroids.1. – IntroductionThe Lyrids are a regular meteor shower, standardly of a weak activity, observedbetween April 14-26. The shower maximum appears on April 21-22 with a zenithal hourlyrate of 5-10 meteors. However, occasionally an enhanced increase of the shower activityexceeding 100 meteors per hour is observed. The first note on a regular appearance of thestream was made by Arago in 1835 [1] and Newton in 1863 [2] in his work on the historyof major meteor showers was able to trace the Lyrids for about 2500 years. The positionof the present shower radiant is at a right ascension of 272◦ and a declination of 34◦.The Lyrids are produced by comet C/1861 G1 Thatcher discovered in April 1861.Its definitive orbit was determined by Oppolzer [3] and the association with the Lyridswas first indicated by Weiss [4]. The mean orbit of the stream based on photographicorbits [5] is very close to the orbit of the comet recalculated to the new equinox andepoch [6]. The comet and stream are moving in the orbits almost perpendicular to theecliptic, with the period of revolution of 415 and about 330 years, respectively.Higher activity of the stream was observed more times in the past. Lindblad andPorubcˇan [7] summarized the Lyrid activity outbursts observed in the last 200 years. Allc© Societa` Italiana di Fisica 423424 V. PORUBCˇAN, L. KORNOSˇ and G. CEVOLANIthe peaks were of a short duration (two hours maximum) and at almost the same so-lar longitudes, approximately a quarter of a day before the main peak. These occasionalactivity enhancements suggest a filamentary structure and mass separation in the stream.Emelyanenko [8] suggests that the activity outbursts in 1803, 1922 and 1982 areprobably due to a libration motion of the orbit near a resonance with Jupiter.The last higher activity maximum observed in 1982 with a half-maximum strengthlasted for only 50 minutes and consisted predominantly of smaller particles [9]. Porubcˇanet al. [10] for this cloud of meteoroids in the orbit 120 years beyond the parent cometsuggested that it could have originated by fragmentation of a larger boulder separatedfrom the comet more revolutions ago.Arter and Williams [11] looked for an explanation of the enhanced Lyrid maximawhich from the older observations indicated a 12 year periodicity [12]. If the maxima ap-pear in multiples of 12 years, it might suggest a resonance motion with Jupiter. Further,they studied [13] evolution of the stream by releasing 20000 model particles from cometThatcher at its last four perihelion passages and followed occurrence of model particlesat the descending node near the Earth. The integration results indicate the occurrenceof higher density parts of the stream in a 12 year cycle.2. – Structure of the Lyrid streamThe most precise information concerning the structure of the stream provides orbitsobtained by photographic methods. Unfortunately, there are little photographic orbits ofthe Lyrids available up to now. Kresa´k and Porubcˇan [14] for an analysis of the showerhad at disposal only 7 Lyrids. Lindblad and Porubcˇan [5] derived the mean orbit of thestream and motion of the radiant on the basis of 14 Lyrids.The latest version of the IAU Meteor Data Center photographic catalogue contains4581 meteor orbits [15] and in the present analysis the stream members were searched forby a search procedure utilizing the Southworth-Hawkins D-criterion [16]. For a limitingTable I. – Orbital and geophysical parameters of the photographic Lyrid meteors (eq. 2000.0).N YY M Day q a e i ω Ω π D α δ Vg(AU) (AU) (◦) (◦) (◦) (◦) (◦) (◦) (km/s)037B1 85 4 21.04 .916 8.980 .898 79.2 215.6 31.1 246.7 .090 271.5 33.0 46.07001W1 50 4 21.35 .918 −6.000 1.153 81.5 213.1 31.4 244.4 .177 270.6 33.1 49.39002W1 50 4 21.37 .911 12.653 .928 79.0 216.4 31.4 247.8 .070 270.8 33.0 46.25007U1 79 4 21.67 .914 10.044 .909 79.7 215.9 31.3 247.1 .081 271.6 32.7 46.40349B1 93 4 21.97 .935 6.585 .858 80.3 212.0 31.9 243.9 .127 274.6 33.2 46.15048E2 96 4 22.07 .922 −25.611 1.036 77.1 213.1 32.3 245.4 .074 270.3 35.1 46.40114J1 52 4 22.35 .918 9.766 .906 78.5 215.2 32.8 248.1 .081 272.3 33.5 45.83004W1 50 4 22.37 .924 46.200 .980 80.2 213.3 32.4 245.7 .013 272.6 33.3 47.23115J1 52 4 22.43 .913 27.667 .967 79.1 215.7 32.9 248.6 .039 271.6 33.2 46.67174N2 82 4 22.79 .913 14.726 .938 78.9 215.9 32.6 248.5 .057 271.6 33.2 46.30032E2 95 4 22.86 .921 −54.176 1.017 79.7 213.5 32.3 245.8 .038 271.8 33.6 47.37079E1 79 4 22.91 .924 61.600 .985 80.5 213.2 32.5 245.7 .018 272.8 33.2 47.40080E1 79 4 22.97 .930 −26.571 1.035 79.7 211.4 32.5 243.9 .070 272.6 34.2 47.50048C1 57 4 23.02 .923 −184.600 1.005 80.6 213.2 33.2 246.4 .033 273.1 33.2 47.63005W1 41 4 23.32 .927 309.000 .997 80.4 212.5 33.6 246.1 .034 273.6 33.5 47.43029B1 84 4 23.92 .929 37.160 .975 80.9 212.4 34.1 246.5 .040 274.6 33.2 47.47064K1 63 4 24.91 .925 −12.500 1.074 80.3 212.3 34.5 246.9 .103 273.3 33.8 48.10Mean .921 46.063 .980 79.7 213.8 32.5 246.3 - 272.3 33.4 47.03s. d. .007 12.658 .072 1.0 1.6 1.0 1.5 - 1.3 .6 .91THE ORBIT, STRUCTURE AND EVOLUTION OF THE LYRID METEOROID STREAM 425value of D = 0.20, 17 meteors from the period April 21-25 belonging to the Lyrid streamwere found (table I). The mean values in table are represented by the arithmetic meanexcept for the semimajor axis which is given as the harmonic mean a = 1/ ¯(1/a).The orbits are compiled from a period of 55 years (1941-1996), which means thatcover only about 13 percent of the orbital period of the parent comet and thus providerather limited information on the distribution of meteoroids along the whole orbit of thestream. The Lyrid radiant daily motion and radiant ephemeris derived from 17 Lyrids isα = 272.3◦ + 0.802◦(Ls − 32.5◦),δ = 33.4◦ − 0.155◦(Ls − 32.5◦).The daily motion in right ascension and declination was found by the least-squaressolution and Ls is the solar longitude of the time of observation for equinox 2000.0 and32.5◦ is the solar longitude of the maximum of activity.To find the size and form of the stream radiant area, individual radiants were reducedto a common solar longitude of the maximum of activity by allowing for the deriveddaily motion of the radiant. The observed radiant area is slightly elongated of a sizeof approximately 5◦ × 2◦, while the reduced radiant area is in the central part moreconcentrated to a size of about 2◦ × 1.5◦.According to the semimajor axis of 17 Lyrids (table I), three distinct groups of orbitscan be separated: a short-period group (6-14 AU), a long-period group (27-61 AU) anda group with extremely long orbits (> 300 AU). The mean orbits of the groups togetherwith the orbit of the parent comet Thatcher are listed in table II.In the next step individual members of the Lyrid short-period and long-period groupwere numerically integrated backwards on a time scale of 5000 years. We have appliedfor the backward integration of the orbital evolution the DE multistep procedure ofAdams-Bashforth-Moulton’s type up to 12th order, with variable step-width, developedby Shampine and Gordon [17] and the positions of perturbing planets were obtainedfrom the Planetary and Lunar Ephemerides DE406 prepared by the Jet Propulsion Lab-oratory [18]. In the integration, each mean orbit is represented by 18 modeled particlesdistributed equidistantly according to the mean anomaly by 20◦ along the mean orbit.Orbital evolution of short-period and long-period group in the semimajor axis a, theexcentricity e, the perihelion distance q, the inclination i is shown in fig. 1 and theevolution in the argument of perihelion ω, the longitude of the ascending node Ω, thelongitude of perihelion π are in fig. 2, together with the orbital evolution of cometThatcher. The last plots of fig. 2 show also the evolution in the heliocentric distance ofthe ascending Ra and descending Rd node. Curves in plots represent individual meteorsmarked in the upper plots (table I).Table II. – Orbital elements and radiants of the Lyrid filaments and orbit of comet C/1861 G1Thatcher (eq. 2000.0).Object Q q a e i ω Ω π α δ Vg n(AU) (AU) (AU) (◦) (◦) (◦) (◦) (◦) (◦) (km/s)short-period 20.0 .918 10.459 .908 78.8 215.5 31.8 247.3 272.1 33.1 46.17 6long-period 85.4 .923 43.157 .977 80.2 213.6 33.0 246.6 272.9 33.2 47.19 4hyperbolic - .924 −20.350 1.045 79.9 212.7 32.8 245.5 272.2 33.8 47.69 7Thatcher 110.4 .9207 55.682 .9835 79.77 213.45 31.87 245.32 272.0 33.5 47.08426 V. PORUBCˇAN, L. KORNOSˇ and G. CEVOLANIFig. 1. – Orbital evolution of the Lyrid short-period orbits (left plots), long-period orbits andcomet Thatcher (right plots) in a, e, q, i over 5000 years.THE ORBIT, STRUCTURE AND EVOLUTION OF THE LYRID METEOROID STREAM 427Fig. 2. – Orbital evolution of the Lyrid short-period orbits (left plots), long-period orbits andcomet Thatcher (right plots) in ω, Ω, π and evolution of the heliocentric distance of the ascending(Ra) and descending node (Rd) over 5000 years.428 V. PORUBCˇAN, L. KORNOSˇ and G. CEVOLANI3. – Discussion and conclusionsThe orbital evolution of the Lyrid parent comet C/1861 G1 Thatcher from a long-termpoint of view was investigated by Porubcˇan and Wu [19]. They have pointed out thepossibility of a capture of the comet into the inner Solar System approximately 300000years ago. It means that practically since that time a stream of meteoroids could beassociated with the comet. In the present study the stream and comet are analysed froma short-term point of view and it can be seen that the orbits of the stream and cometare relatively stable (figs. 1 and 2).The orbits in the plots divided into two groups can be designated as a “short-periodfilament” and a “long-period filament”. Integration of Lyrids on extreme orbits of whichsix are hyperbolic has indicated that these are most probably the result of measurementerrors. No one of these meteoroids before the collision with the Earth had a closerapproach to a larger perturbing body which would accelerate it to a hyperbolic orbit.Individual meteors in figs. 1 and 2 are depicted by different curves and labeled usingtheir designation in the IAU Meteor Database catalogue. Also the evolution of the orbitof comet Thatcher is indicated in the plots of long-period filament. It is evident thatmeteors pertinent to this filament are moving in the orbits very close to the comet duringthe whole period of integration.Summarizing, based on photographic observations, two very distinct groups of or-bits, short-period and long-period, can be recognized in the Lyrid meteor stream. Thegroups were probably formed under the gravitational influences of planets on the stream.Integration of orbits of short-period group indicates that this branch of the stream isaffected predominantly by Jupiter. Long-period set of orbits is modified also by Saturn.The ascending nodes of orbits of short-period group lay between Jupiter and Saturn.The evolution of long-period Lyrid group is more stable and its members have similarevolution as the parent comet Thatcher. The ascending nodes are close to the orbitof Saturn. The descending nodes of all orbits are stable and close to the Earth. Thehyperbolic Lyrid orbits are most probable due to not enough precise measurements.∗ ∗ ∗The authors are indebted for the support of the research to VEGA, the Slovak GrantAgency for Science, grant No. 1/3067/06.REFERENCES[1] Lovell A. C. B., Meteor Astronomy (Clarendon Press, Oxford) 1954.[2] Newton H. A., Am. J. Sci. (II), 36 (1863) 145.[3] Oppolzer T., Astron. Nachr., 62 (1864) 187.[4] Weiss E., Astron. Nachr., 68 (1867) 382.[5] Lindblad B. A. and Porubcˇan V., Bull. Astron. Inst. Czech., 42 (1991) 354.[6] Marsden B. G., Catalogue of Cometary Orbits (IAU Minor Planet Center) 1989.[7] Lindblad B. A. and Porubcˇan V., in Asteroids, Comets, Meteors 1991, June 24-281991, Flagstaff, USA, edited by Harris A. W. and Bowell E., p. 367.[8] Emelyanenko V. V., Astron. Vestn., 24 (1990) 308.[9] Adams M. T., Meteor News, 58 (1982) 1.[10] Porubcˇan V., Sˇtohl J. and Svorenˇ J., Contrib. Astron. Obs. Skalnate Pleso, 32(1992) 25.[11] Arter T. R. and Williams I. P., Mon. Not. R. Astron. Soc., 277 (1995) 1087.[12] Guth V., Bull. Astron. Inst. Czech., 1 (1947) 1.THE ORBIT, STRUCTURE AND EVOLUTION OF THE LYRID METEOROID STREAM 429[13] Arter T. R. and Williams I. P., Mon. Not. R. Astron. Soc., 286 (1997) 163.[14] Kresa´k L. and Porubcˇan V., Bull. Astron. Inst. Czech., 21 (1970) 153.[15] Lindblad B. A., Neslusˇan L., Porubcˇan V. and Svorenˇ J., Earth, Moon, andPlanets, 93 (2005) 249.[16] Southworth R. B. and Hawkins G. S., Smithson. Contr. Astrophys., 7 (1963) 261.[17] Shampine L. F. and Gordon M. K, Computer Solution of Ordinary DifferentialEquations (Freeman and Comp., San Francisco) 1975.[18] Standish E. M, JPL IOM (1998) 312.F - 98 - 048.[19] Porubcˇan V. and Wu Z., Meteor Rep. Slovak Astron. Soc., 15 (1994) 18.

The orbit, structure and evolution of the Lyrid meteoroid stream

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The orbit, structure and evolution of the Lyrid meteoroid stream

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