A&A 373, 329–335 (2001) Astronomy DOI: 10.1051/0004-6361:20010583 & c ESO 2001 Astrophysics Search for meteor showers associated with Near-Earth Asteroids I. Taurid Complex P. B. Babadzhanov? Institute of Astrophysics, Tajik Academy of Sciences, Dushanbe 734042, Tajikistan and Isaac Newton Institute of Chile, Tajikistan Branch Received 26 December 2000 / Accepted 20 March 2001 Abstract. Observed meteor showers associated with some Near-Earth asteroids (NEAs) is one of the few criteria that such asteroids may be considered to be candidate extinct cometary nuclei. In order to reveal new NEA- meteor shower associations, we calculated the secular variations of the orbital elements of 17 Taurid Complex asteroids with allowance for perturbations from six planets (Mercury-Saturn) over one cycle of variation of perihelia arguments. The Earth-crossing class of these NEAs and theoretical geocentric radiants and velocities of their meteor showers were determined and compared with available observational data. It turns out that each Taurid Complex asteroid is associated with four meteor showers. This is evidence for the cometary origin of these asteroids. Key words. comets – meteoroids; meteors – minor planets, asteroids 1. Introduction theoretical radiants suggested by Hasegawa (1990) and known as the ω-method is more appropriate and takes into It is generally accepted that meteoroid streams are formed account the fact that a meteoroid stream can give rise to as a result of the disintegration of cometary nuclei. The a meteor shower only when the orbits of the stream mete- presence of meteor showers associated with some near- oroids cross the Earth’s orbit. However, this method also Earth asteroids (NEAs) is evidence that such asteroids does not predict the radiants of all possible meteor showers have a cometary origin, i.e. they are extinct cometary nu- of the given near-Earth object and is used only for comets clei (Olsson-Steel 1988; Steel 1994; Babadzhanov 1996; and minor planets with an orbital node currently situated Lupishko 1998). The existence of asteroids identifiable at no more than 0.2–0.3 AU from the Earth’s orbit. with extinct or dormant comets (2060 Chiron, 4015 As follows from basic principles of meteoroid stream Willson-Harrington, 1986 TF Parker-Hartley) confirm the formation and evolution (Babadzhanov & Obrubov 1987, cometary origin for some NEAs. 1992; Babadzhanov 1996; Steel 1994), related meteor Investigation of NEA-meteor shower associations is im- showers can be produced also by those comets whose or- portant not only for confirmation or denial of the NEA bits are presently located at distances more than 0.3 AU cometary origins, but also to obtain important informa- from the Earth’s orbit but which crossed it in the past. tion about NEA sources – comets from outer regions of The orbit of the parent body when crossing the Earth’s the Solar system, and real asteroids from the main belt. orbit can be determined by studying its evolution under The calculation of theoretical meteor radiants is the the gravitational perturbing action of the major planets. first step in revealing the generic relationship between a given near-Earth object (comet or asteroid) and its possi- 2. Formation of meteoroid streams ble meteor showers. However, methods for the determi- nation of the theoretical radiants of comets and aster- Ejection velocities of meteoroids from their parent bodies oids approaching the Earth’s orbit close than 0.1–0.3 AU, and radiation pressure (for small particles) cause an ini- which were used by different authors (e.g., Kramer 1973; tial dispersion in orbital elements of ejected meteoroids. Drummond 1982, 2000; Artoos 1994) until recently, did Because of differences in the semi-major axes (and orbital not take into account the meteoroid stream evolution and periods) between the meteoroids and their parent body, could only roughly predict one or two radiants of the some meteoroids lag behind the parent body, while oth- given comet or asteroid. The method of the calculation of ers, overtaking it, spread along the entire orbit and form a complete loop in a comparatively short time (Hughes ? e-mail: [email protected] 1986; Williams 1995). Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20010583 330 P. B. Babadzhanov: Search for meteor showers associated with Near-Earth Asteroids. I. possible evolutionary positions distinguished by their ar- guments of perihelia ω. For example, to simulate the form of Poseidon’s meteoroid stream we consider its osculat- ing orbits for the period of one cycle of variation of ω. The projection of Poseidon’s orbit onto the plane per- pendicular to the ecliptic is presented in Fig. 1a, and the three-dimensional image of these orbits is given in Fig. 1b. A characteristic feature of the form obtained is its large thickness in the aphelion region and the symmetry with respect to the ecliptic plane near which the disturbing planets are moving. If the Earth’s orbit is assumed to be circular, then it may be intersected by those stream meteoroids which have the orbital node at the heliocentric distance r ≈ 1 AU, i.e. satisfying the expression: a(1 − e2) − 1 cos ω ≈ , (1) e where a is the semi-major axis and e is the eccentricity. As shown earlier (Babadzhanov & Obrubov 1987, 1992; Babadzhanov 1996) the number of meteor show- ers produced by a meteoroid stream is determined by the Earth-crossing class of the parent-body orbit. For exam- ple, if it is a quadruple-crosser of the Earth’s orbit (i.e. during one cycle of variation of the perihelion argument of its orbit under the perturbing action of the major planets, a parent body crosses the Earth’s orbit four times) the me- teoroids of the stream that separated from its parent might produce four meteor showers: two at the pre-perihelion intersections and two at the post-perihelion intersections with the Earth (Fig. 1c). Crossing before perihelion gives rise to two night-time showers, and after the perihelion, two daytime showers. These two pairs of showers are Fig. 1. a) The projection of Poseidon’s orbits onto the plane formed by the same meteoroid stream, each pair consist- perpendicular to the ecliptic; b) three dimensional image of ing of a northern and a southern branch. For example, the Poseidon’s orbits for the period of one cycle of variation of the meteoroid stream of comet Encke produces night-time ω; c) mean orbits of Poseidon’s stream meteoroids producing Northern and Southern Taurids and daytime ζ-Perseids 4 meteor showers. and β-Taurids showers. ζ-Perseids are the northern branch of the shower at daytime and are twins of the Northern Taurids, but β-Taurids are the southern branch at the After the meteoroids are distributed along the orbit daytime intersections of the stream and are twins of the of the parent body, due to differences in the planetary Southern Taurids. perturbing action on stream meteoroids of different semi- According to the foregoing notion of meteoroid-stream major axes and eccentricities, the rates and cycles of vari- evolution, we use a new method for the determination of ations in the angular orbital elements (the argument of theoretical radiants of the near-Earth objects. It consists perihelia ω, the longitude of the ascending node Ω, and the of the following operations: inclination to the ecliptic i) will be different for different meteoroids. As a result, the orbits of different meteoroids (1) The calculation of secular variations of the cometary will be at different evolutionary stages, as distinguished (or asteroidal) orbital elements for a time interval by their arguments of perihelia, i.e. the stream meteoroids covering one cycle of variation of the argument of occupy all evolutionary tracks of their parent body. This perihelia; process increases considerably both the size of the mete- (2) The determination of the orbits crossing the Earth’s oroid stream and its thickness (the breadth of a stream is orbit, and of the Earth-crossing class of the parent determined by the value of the meteoroids’ orbital semi- body, i.e. the number of crossings during one cycle of major axes). the perihelion argument. The number of crossing may In order to imagine the form of the meteoroid stream be from one to eight; let us assume that the stream consists of particles (3) The calculation of the theoretical geocentric radiants of approximately the same semi-major axis but in all and velocities for the Earth-crossing orbits; P. B. Babadzhanov: Search for meteor showers associated with Near-Earth Asteroids. I. 331 Table 1. Near-Earth Asteroids of the Taurid Complex. ◦ ◦ ◦ ◦ Asteroid qaeiΩ ω π DHd Ra Rd AU AU 2000.0 km AU AU 1991 TB2 0.394 2.397 0.836 8.6 297.2 195.6 132.8 0.13 17.0 1.9 3.7 0.4 5143 Heracles 0.420 1.834 0.771 9.2 310.8 226.4 177.2 0.13 13.9 7.7 1.6 0.5 1996 SK 0.494 2.428 0.796 2.0 198.3 283.4 121.7 0.12 17.0 1.9 0.7 1.1 1993 KA2 0.502 2.227 0.775 3.2 239.6 261.3 140.9 0.06 29.0 0.01 1.0 0.8 4197 1982 TA 0.522 2.297 0.773 12.2 10.2 119.2 129.4 0.14 14.5 5.9 1.5 0.7 6063 Jason 0.522 2.216 0.764 4.8 170.0 336.5 146.5 0.07 15.1 4.5 0.5 3.1 4341 Poseidon 0.588 1.835 0.679 11.9 108.2 15.5 123.7 0.20 15.6 3.5 0.6 2.9 2201 Oljato 0.630 2.176 0.711 2.5 76.9 96.0 172.9 0.12 15.3 4.1 1.2 1.0 5025 P-L 0.647 2.140 0.697 3.1 341.6 153.8 135.5 0.12 15.9 3.1 2.9 0.7 1991 GO 0.663 1.956 0.661 9.7 25.0 88.6 113.6 0.19 19.0 0.7 1.1 0.9 1995 FF 0.674 2.321 0.710 0.6 175.6 293.1 108.7 0.14 26.5 0.02 0.9 1.6 1991 BA 0.713 2.242 0.682 2.0 118.9 70.7 189.6 0.15 28.5 0.01 1.0 1.6 4183 Cuno 0.718 1.980 0.637 6.8 295.9 235.2 171.1 0.19 14.5 5.9 1.8 0.9 8201 1994 AH2 0.730 2.527 0.711 9.6 164.4 24.8 189.2 0.20 16.3 2.6 0.8 3.5 1990 HA 0.782 2.571 0.696 3.9 184.8 308.3 133.1 0.20 16.0 3.0 0.9 2.3 5731 Zeus 0.785 2.262 0.653 11.6 282.8 215.6 138.4 0.19 15.5 3.7 2.8 0.8 1996 RG3 0.790 2.000 0.605 3.6 158.5 299.9 98.4 0.20 18.5 0.9 1.0 1.8 2P/Encke 0.331 2.209 0.850 11.9 334.7 186.3 161.0 2.4 4.0 0.3 (4) Search for theoretically predicted radiants in cata- is a modified Southworth & Hawkins’ (1963) criterion of logues of observed meteor showers and of individual orbital similarity as applied to the membership for the meteors.