1. 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.

2. 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
,

3. 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

4. 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.

5. 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.

6. 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.

7. 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.
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