The Origin Of The 1998 June BoöTid Meteor Shower
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The Origin Of The 1998 June BoöTid Meteor Shower

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The Origin Of The 1998 June BoöTid Meteor Shower The Origin Of The 1998 June BoöTid Meteor Shower Document Transcript

  • THE ORIGIN OF THE 1998 JUNE BOÖTID METEOR SHOWER TOMOYASU TANIGAWA and TAKEMA HASHIMOTO The Nippon Meteor Society, 3-7-1 Kita-Rokkodai, Nishinomiya 6511413 Japan (E-mail: tanigawa@bird.zero.ad.jp) (Received 11 February 2000; Accepted 12 September 2001) Abstract. We compare various objects as the possible parent comet of the 1998 June Boötid, by using the Tisserand invariant and the D-discriminant. Furthermore, in order to investigate the behaviour of the meteoric stream orbit, we simulate the orbital evolution of test particles that are released from 7P/Pons–Winnecke. We show firstly that the parent comet of the 1998 June Boötids, is 7P/Pons–Winnecke, and secondly that the meteoroids which constitute 1998 June Boötids were released in 1819 and 1869 from the parent comet. In the mid-1900s the meteoroids started to transfer to Earth-colliding orbits by Jovian perturbations. Keywords: 1998 June Boötids, orbital evolution, Pons–Winnekids 1. Introduction On 27 June 1998, the meteor shower, with a radiant point around Boötes, appeared suddenly. This meteor shower recorded a maximum zenith hourly rate (ZHR) 270 (Arlt et al., 1999; Hashimoto and Osada, 1998). Judging from the season and the radiant point, this meteor shower seemed to be June Boötid associate with the comet 7P/Pons–Winnecke. Pons–Winnekids is noted for a strong display in 1916, and good displays in 1921 and 1927 (Denning, 1916; Yamamoto, 1922; Svoboda, 1927; Sytinskaja, 1928). Pons–Winnekids has shown very weak activity in recent years. Why did the 1998 June Boötid appear, suddenly? Though 7P/Pons– Winnecke has been largely perturbed by Jovian gravity, its orbit has not altered in order for it to pass near the Earth, and 7P/Pons–Winnecke has not shown notable cometary activity, lately. There is a small possibility that another comet produced the 1998 June Boötids. In order to reveal the origin of the 1998 June Boötid, we research the parent comet of this meteor shower by using the Tisserand invariant and D-discriminant, and simulate the motion of the test particle that is released from parent object, in order to research the orbital evolution. 2. Tisserand Invariant and D-Discriminant In Czechoslovakia, Spurny and Borovioka (1998) observed the fire ball, EN270698, that belonged to the 1998 June Boötid, and obtained orbital elements. Earth, Moon and Planets 88: 27–33, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.
  • 28 TOMOYASU TANIGAWA AND TAKEMA HASHIMOTO We calculate the Tisserand invariant and D-discriminant for EN270698 and some other comets, in order to conclude the parent comet of the 1998 June Boötid. 2.1. T ISSERAND INVARIANT When a cometary orbit is perturbed by the gravity of a planet, the orbital elements are altered. But the Tisserand invariant is almost constant (Tisserand, 1896). If some Tisserand invariants are kept within ±0.01, it means that they are from the same object (Kresak, 1972). The Tisserand invariant is given by, T = 2 1 + a aj a(1 − e2 ) × cos I, aj where a is a semi-major axis, e is eccentricity, I is inclination (on the basis of the Jovian ecliptic plane) and aj is a Jovian semi-major axis. The Tisserand invariant of EN270698 is 0.5149. We calculate the Tisserand invariant (T ) for all periodic comets. We choose some comets of which T = 0.5149(EN270698) ± 0.01, and perihelion distance (q) is smaller than 1.2 AU, as candidates of parent comets. By using the result, 7 periodic comets, for example 103P/Hartley2, 7P/Pons–Winnecke, 18D/Perrins–Mrkos, 6P/d’Arrest, D/1766 G1 Helfenzrieder, P/1994 P1 and Machholtz2, and its 30 orbits are listed. 7P/Pons–Winnecke’s value, especially that of orbit in 1954 and 1951 (T = 0.5148), is nearest to EN270698 among them. We listed in Table I, Tisserand invariants of two other comets too; 73P/Schwassmann–Wachmann3 is associated with the τ Herculids which was observed on June 10, 1930 and D/1770 L1 Lexell which was close to the Earth in 1770, seemed to produce a meteor shower in early July. 2.2. D- DISCRIMINANT As well as the Tisserand invariant, the D-discriminant has been used to identify a meteor and its parent object. D-discriminant is calculated using the orbital elements, i.e., perihelion distance (q), eccentricity (e), inclination (i), ascending node (L) and argument of perihelion (ω), of the different two objects. D was defined by Southworth and Hawkins (1963) as D= 2 2 2 2 d1 + d2 + d3 + d4 , where 2 d1 = (q1 − q2 )2 , 2 d3 I = 2 sin 2 2 d2 = (e1 − e2 )2 , 2 2 , 2 d4 = (e1 + e2 ) sin 2 ,
  • THE ORIGIN OF THE 1998 JUNE BOÖTID METEOR SHOWER 29 TABLE I Comparison of the Tisserand invariant and the D-discriminant. Each comets’ T and D are calculated using the orbital elements that are obtained in the year, shown in ( ) below Object T D EN270698 7P/Pons–Winnecke (1869) 73P/Schwassmann–Wachmann3 (1930) D/1770 L1 Lexell (1770) 0.5149 0.5113 0.5338 0.5022 0 0.1284 0.1449 1.0529 and I = arccos(cos i1 cos i2 + sin i1 sin i2 cos(L1 − L2 )) and = ω1 − ω2 + 2 arcsin cos L1 − L2 I i1 + i2 sin sec . 2 2 2 We calculate the D-discriminant for EN270698 and candidate objects (Table I). 7P/Pons–Winnecke’s D-discriminant is the lowest value. Because consideration of these two parameters and the radiant point is the nearest to the predicted point (Hasegawa, 1990), α = 213.4◦ , δ = +47.5◦ . The availability of orbital elements for EN270698 allows us to use it as one of the two orbits (i.e., the reference orbit) in the D-discriminant. We conclude that 7P/Pons–Winnecke is the parent comet of 1998 June Boötid meteor shower. 3. Simulation In order to research the orbital evolution, we simulate the motion of test particles which are released from 7P/Pons–Winnecke. 7P/Pons–Winnecke has been recorded as the orbital element from its discovery, except some returns to perihelion (Marsden and Williams, 1992). We released 1000 test particles before and after every perihelion passage for which orbital elements are available, i.e., a total of 2000 test particles are released per revolution while the comet 7P/Pons–Winnecke has a heliocentric distance r less than 2 AU. We released test particles in all directions, at time interval k · r 2 per day (k, constant; r, heliocentric distance), and the released relative initial velocity to cometary nucleus is 10–100 m/s decided by random number. We consider the gravitational perturbation of 9 planets and the moon. We neglect the effect of solar radiation pressure force, because we assume
  • 30 TOMOYASU TANIGAWA AND TAKEMA HASHIMOTO Figure 1. YGD of the 1819, 1869 and 1921’s test particles are plotted. YGD means the minimum geocentric distance among 2000 test particles, from 15 June to 15 July in every year. When the YGD is larger than 0.1 AU (0.5 AU on 1921’s test particles), we do not plot them. The other year’s YGD (though it is not plotted) is large, as is 1921’s YGD. the dust particle is larger than millimeter-sized. We integrate the motion equations of test particles, using the Bulirsch–Stoer method with 10−8 precision (Press et al., 1992). Every year, from 15 June to 15 July, we measure the geocentric distance of all test particles in a 0.2 day interval. We decide “yearly geocentric distance (YGD)” is the minimum geocentric distance of all measurement in a year. For expectation of re-appearance, we will calculate yearly geocentric distance until 2010. 4. Results and Discussion We released test particles when the 7P/Pons–Winnecke return to perihelion. In this paper, for example “1819’s test particles” stands for the test particles which were released in 1819. It is only 1819 and 1869’s test particles that can be close to the Earth (Figure 1). The minimum geocentric distance of the 1819’s test particles was 0.00672 A.U., and the 1869’s test particles was 0.00323 A.U. The other test particles, for instance, the 1921’s test particles, are not close to the Earth, because they move along the parent comet’s orbit. We plotted the 1921’s test particles in Figure 1, as an example of years other than 1819 and 1869’s test particles.
  • THE ORIGIN OF THE 1998 JUNE BOÖTID METEOR SHOWER 31 TABLE II The number of the test particle, within 0.05 A.U. close to the Earth Released year Year 1916 1921 1927 1998 2010 1819 1869 1921 1 0 – 1 6 – 13 14 30 7 6 0 1 3 0 Table II shows how many test particles are close to the Earth within 0.05 AU, when the YGD was recorded. We also provide the number of the particles from 1916 to 1927, while the Pons–Winneckids was very active. Beside them, there are few years when the test particles were close to the Earth within 0.05 AU. By these results, we find that the 1819’s and 1869’s test particles were close to the Earth statistically. The year 1998 is special for the Pons–Winneckids. After 1999, any test particles will not be close to the Earth. Not until 2010, will the test particles be close to the Earth again. We clear the process of the orbital evolution. We focus on one of the 1869’s test particles which records the YGD, and research the changes of orbital evolution (Figure 2). Perihelion distance, inclination and eccentricity began to break away from the parent comet’s orbital elements, about 1940. They are perturbed by Jovian gravity, because the apogee of the test particles is near the Jovian orbit, and the orbit of the particles turns to transfer and collide with the Earth. 5. Conclusion The following conclusions were derived from the results and discussion. 1. The parent object of the 1998 June Boötid meteor shower is 7P/Pons– Winnecke. 2. The meteors of the 1998 June Boötid meteor shower are released from the 7P/Pons–Winnecke in the years 1819 and 1869. 3. In about 1940, the orbit of the meteors which belong to 1998 June Boötid meteor shower, began to break away from the parent body’s orbit by Jovian perturbation, and turns to collide with the Earth. 4. Pons–Winneckids was not observed in 1999. This agrees with the result of our computer simulation. 5. Next activity of the Pons–Winneckids will be in 2010.
  • 32 TOMOYASU TANIGAWA AND TAKEMA HASHIMOTO Figure 2. Changes of orbital elements of the 1869’s test particle which produce the YGD (0.00311 AU) in 1998. (a) Perihelion distance, (b) eccentricity, (c) inclination, (d) argument of pericenter. For reference, the changes of 7P/Pons–Winnecke (PW) and the 1921’s test particles are also plotted. 1921’s test particles are not close to the Earth, because they move along the mother comet’s orbit.
  • THE ORIGIN OF THE 1998 JUNE BOÖTID METEOR SHOWER 33 Acknowledgements The authors express their sincere thanks to Prof. T. Mukai and the members of the Solar System Physics Group of Kobe University for advice on this work. We are grateful to Ms. F. Millines of Amagasaki High School for checking the manuscript. References Arlt, R., Rendtel, J., Brown, P., Velkov, V., Hocking W. K., and Jones, J.: 1999, ‘The 1998 Outburst and History of the June Boötid Meteor Shower’, Mon. Not. Roy. Astron. Soc. 308, 887–896. Denning, W. F.: 1916, ‘Remarkable Meteoric Shower on June 28’, MNRAS 76, 740–743. Hasegawa, I.: 1990, ‘Predictions of the Meteor Radiant Point Associated with a Comet’, Pabl. Astron. Soc. Japan 42, 175–186. Hashimoto, T. and Osada, K.: 1998, ‘June Boötid Outburst: Optical Observations from Japan’, WGN, J. IMO 26, 263. Kresak, L.: 1972, ‘Jacobian Integral as a Classificational and Evolutionary Parameter of Interplanetaery Bodies’, Bull. Astron. Inst. Chechosl. 23, 1–34. Marsden, G. B. and Williams, G. V.: 1992, ‘Catalogue of Cometary Orbits Seventh Edition’, IAU Central Bureau for Astronomical Telegrams and Minor Planet Center. Press, W. H., Flannery, B. B., Teukolsky, S. A., and Vetterling, A.: 1989, Numerical Recipes in C, Cambridge. Spurny, P. and Borovicka, J.: 1998, IAU Circ. 6973. Southworth, R. B. and Hawkins, G. H.: 1963, ‘Statistics of Meteor Streams’, Smithson. Contrib. Astrophys. 7, 261. Svoboda, H.: 1923, Astron. Nachr. 218, 255. Sytinskaja, N.: 1928, Publ. Tashkent Astron. Obs. 1, 91. Tisserand, F.: 1896, Trité de Mécanique Céleste Tom IV, Gautheier-Villars, p. 203. Yamamoto, I.: 1922, Observatry 45, 81.