IMO Results: June Bootids 1998

**International Meteor Organization (IMO)**

Surprising Activity of the 1998 June Bootids

Jürgen Rendtel, Rainer Arlt, and Valentin Velkov

Published in WGN, the Journal of IMO 26:4, p. 165-172 (1998)

Abstract: After a quiescent period of several decades, the June Bootid meteor shower (sometimes referred to as June Draconids) surprised a number of regular and casual observers by an outburst with maximum ZHRs near 100. A total number of 619 meteors was recorded during regular meteor observations. An average population index of r=2.22±0.07 was derived from 511 magnitude estimates. The broad activity profile with high rates for more than 10 hours and the large radiation area in 1998 resemble the appearance of the 1916 and 1927 outbursts. The peak time is found to be between lambda=95.7° and sol=96.0° (eq. 2000.0); the average radiant is alpha=230° and delta=+47°.

Introduction

Considerable activity of the June Bootids was observed at two occasions in 1916 and 1927. Some sources also list the year 1921, but the activity reported from this return is rather low (see Table 1). Additionally, there are some reports of possible activity before and after these returns, but the association to the June Bootids is not certain. Nevertheless, Hoffmeister [1] considered the shower (listed as June Draconids on p. 88) as a ``real shower,'' which was excluded from his final catalogue only because of insufficient observation. When the current IMO working list of meteor showers was established by Arlt [2], the shower was rejected because its regular activity was practically below the detection limits for many years. However, June is a period of the year which is poorly covered by meteor observations generally, and in particular from the northern hemisphere.

Observers were surprised by a high meteor activity in the night June 27-28, 1998. The display attracted the attention of casual witnesses, because there were numerous bright meteors visible.
Due to the short duration of northern summer nights, there were not many reports of regular observers.

In total, we received reports or notes from 42 observers from 13 countries:

E. Bojurova (Bulgaria), P. Brown (Canada, radar), G. Carstairs (Australia), S. Crivello (Italy), M. Dionisi (Italy), B. Ewen-Smith (Portugal), D. Girling (Australia), R. Gorelli (Italy), V. Grigore (Romania), R. Haver (Italy), W.K. Hocking (Canada, radar), T. Hashimoto (Japan), T. Holmes (UK), D. Ito (Japan), K. Izumi (Japan), P. Jenniskens (USA), J. Kac (Slovenia), K. Kerr (Australia), A. Knöfel (Germany), H.G. König (Germany), K. Kretsch (Ireland), R. Ma\v{n}\'ak (Czech Republic), A. Marsh (Australia), A. McBeath (UK), S. Näther (Germany), A. Negoescu (Romania), K. Nose (Japan, video), K. Osada (Japan), D. Penn (Portugal), L. Rashkova (Bulgaria), J. Rendtel (Germany), K. Sato (Japan), L.R. Sobkoviak (USA), E. Stomeo (Italy), P. Sütterlin (Germany), K. Suzuki (Japan, forward scatter), M. Taylor (USA), J.M. Trigo (Spain), M. Ueda (Japan, forward scatter), B. Vanderwark (USA), V. Velkov (Bulgaria, visual, photographic), R. Vodicka (Australia).

The activity of the June Bootids was also evident in forward-scatter and radar data. The first note about increased activity came from Japan (Koseki 1998, IMO News), reporting counts that were three to five times higher after 9h UT, continuing to at least 14h UT, on June 27. One witness gave a number of 50 meteors per hour seen from inside an observatory dome.

Table 1 : Historical records of the June Bootid activity during the 1916, 1921, and 1927 returns of the shower. Rates do not refer to the term ZHR which is in use nowadays, but give only numbers per hour independent of the observing conditions. Other papers just give numbers of shower meteors noted by the observer.

Time (UT) Activity Observer, remarks Source
1860, 1861 Jun 30 ``many'' Lowe Denning [7]

1916 Jun 28 22h25m-00h10m 55 met. Denning Denning [7]

1916 Jun 29 00h45m-01h15m 14 met. partly cloudy Denning [7]

1921 Jun 24 2.9/h summary Hoffmeister [8]

1921 Jun 25 2.5/h summary Hoffmeister [8]

1921 Jun 26 0.6/h summary Hoffmeister [8]

1921 Jun 28 7 met. Denning Kronk [9]

1921 Jun 28 1.7/h summary Hoffmeister [8]

1921 Jun 28 21h45m-22h50m 5 met. 3 observers, Prague;hazy and cirrus Prey [10]

1921 Jun 28 21h50m-24h00m 5.5/h Stepanek, Ondrejov Svoboda [11]

1921 Jun 28 23h00m-01h10m ~20 JBO Jadot Jadot [12]

1921 Jun 29.17 7 met. Dole, USA Kronk [9]

1921 Jun 29 1.1/h summary Hoffmeister [8]

1921 Jun 29 21h35m-23h10m 2 met. Mrazek, Prague; very hazy Prey [10]

1921 Jun 30.10 8 met. Dole, USA Kronk [9]

1921 Jun 30 21h10m-00h50m ~20 JBO Jadot Jadot [12]

1921 Jul 01 22h00m-23h00m 6 met. Heybrock, Frankfurt hazy, clouds Heybrock [13]

1921 Jul 03 153 met. Nakamura Yamamoto questioned by Denning [14],

1927 Jun 24.8 54/h 236 met., 2 obs., Tashkent Sytinsky [3]

1927 Jun 25.8 96/h 316 met., 2 obs., Tashkent Sytinsky [3]

1927 Jun 26.8 213/h 1054 met., 2 obs., Tashkent Sytinsky [3]

1927 Jun 27.8 357/h 1213 met., 2 obs., Tashkent Sytinsky [3]

1927 Jun 26-30 145 met. Dole, USA King [16]

Time (UT)	Activity	Observer, remarks	Source
1860, 1861 Jun 30	``many''	Lowe	Denning [7]
1916 Jun 28 22h25m-00h10m	55 met.	Denning	Denning [7]
1916 Jun 29 00h45m-01h15m	14 met.	partly cloudy	Denning [7]
1921 Jun 24	2.9/h	summary	Hoffmeister [8]
1921 Jun 25	2.5/h	summary	Hoffmeister [8]
1921 Jun 26	0.6/h	summary	Hoffmeister [8]
1921 Jun 28	7 met.	Denning	Kronk [9]
1921 Jun 28	1.7/h	summary	Hoffmeister [8]
1921 Jun 28 21h45m-22h50m	5 met.	3 observers, Prague;hazy and cirrus	Prey [10]
1921 Jun 28 21h50m-24h00m	5.5/h	Stepanek, Ondrejov	Svoboda [11]
1921 Jun 28 23h00m-01h10m	~20 JBO	Jadot	Jadot [12]
1921 Jun 29.17	7 met.	Dole, USA	Kronk [9]
1921 Jun 29	1.1/h	summary	Hoffmeister [8]
1921 Jun 29 21h35m-23h10m	2 met.	Mrazek, Prague; very hazy	Prey [10]
1921 Jun 30.10	8 met.	Dole, USA	Kronk [9]
1921 Jun 30 21h10m-00h50m	~20 JBO	Jadot	Jadot [12]
1921 Jul 01 22h00m-23h00m	6 met.	Heybrock, Frankfurt hazy, clouds	Heybrock [13]
1921 Jul 03	153 met.	Nakamura	Yamamoto questioned by Denning [14],
1927 Jun 24.8	54/h	236 met., 2 obs., Tashkent	Sytinsky [3]
1927 Jun 25.8	96/h	316 met., 2 obs., Tashkent	Sytinsky [3]
1927 Jun 26.8	213/h	1054 met., 2 obs., Tashkent	Sytinsky [3]
1927 Jun 27.8	357/h	1213 met., 2 obs., Tashkent	Sytinsky [3]
1927 Jun 26-30	145 met.	Dole, USA	King [16]

Previous observations of the June Bootids

In this section, we give a summary of old observations of the June Bootids regarding their activity. We restrict to those returns where a considerable rate was reported from several locations. Most observers made plots, even when high rates were present. For the 1927 return, plots and counts were made by different observers of the Tashkent group (Sytinsky [3]; detailed report by Sytinskaya [4]). Please note that there are no data for the further reduction, such as the limiting magnitude. The data are also difficult to compare with one another.
The June Bootid activities of 1916, 1921, and 1927 are quite well-documented in the literature. The meteors were often described as faint, but at the same time there were reports of bright meteors and fireballs. A magnitude -14 June Bootid fireball was photographed on June 29, 1927 (Yamamoto [5]). Denning [6] immediately associated the shower with comet 7P/Pons-Winnecke, a comet of the Jupiter family. Relatively close encounters with Jupiter caused quite rapid changes of the comet's orbit. These changes shifted the perihelion from inside the Earth's orbit (until 1916) to outside the Earth's orbit (from 1921). The minimum distance between the orbits increased continuously after the 1921 perihelion passage and reached 0.24 AU in 1998 (Figure 1). So, it is quite unlikely that recently released meteoroids approached the Earth in 1998. The event, which is described next, must be linked to meteoroids ejected from the parent comet 7P/Pons-Winnecke earlier in this century.
Contrary to most known outbursts of meteor showers, the June Bootid activity lasted for more than 12 hours. This was also reported from the observations in 1916 and 1927. Obviously, there was no relation to the actual comet position: the 1916 activity happened almost 300 days after the last perihelion passage (with q=0.970605 AU). The 1927 event occurred just 7 days after the comet passed its perihelion (then q=1.039235 AU). When 7P/Pons-Winnecke passed the perihelion (now q>1.25 AU) last on January 2, 1996, the entire orbit was distant from the Earth's orbit (Figure 1). The orbital data of the comet were taken from [17]. Given the current distance between the orbits of the comet and the Earth, such an enhanced activity was not to be expected. Furthermore, the encounter conditions of the 1998 June Bootid outburst are of a different type compared to the earlier events of this shower and also compared to the peaks of the Draconids, Leonids, and Perseids, for example.

[Earth-Comet distance]

Figure 1: Evolution of the minimum distance of the orbit of 7P/Pons-Winnecke from the Earth's orbit.

[1998 June Bootid ZHR]

Figure 2: ZHR profile of the 1998 June Bootids. The values are based on a population index of r=2.22 and a radiant position at alpha=230° and delta=+47°.

Table 2 : Profile of the average ZHR values for the 1998 June Bootids. ``Obs.'' is the number of individual rates involved in the average and JBO is the number June Bootid meteors; solar longitudes refer to eq. 2000.0.

Date Time (UT) lambda Obs. JBO ZHR

June 26 23h10m 95.16° 3 13 13±8

June 27 07h30m 95.464° 1 28 10±4

June 27 10h20m 95.603° 1 21 66±29

June 27 11h50m 95.662° 1 25 102±41

June 27 19h30m 95.983° 3 40 91±29

June 27 20h10m 95.993° 6 68 66±16

June 27 20h40m 96.014° 6 69 59±14

June 27 21h20m 96.036° 8 97 63±13

June 27 21h50m 96.056° 14 150 50±8

June 27 22h10m 96.072° 11 102 48±10

June 27 22h40m 96.093° 14 155 60±10

June 27 23h20m 96.122° 14 113 53±10

June 28 00h00m 96.144° 14 114 50±9

June 28 00h40m 96.167° 10 81 53±12

June 28 01h00m 96.187° 6 33 39±14

June 28 01h20m 96.199° 2 8 24±17

June 28 12h20m 96.64° 1 0 0

June 29 11h00m 97.53° 6 6 2±2

June 29 21h00m 97.93° 1 0 0

Date	Time (UT)	lambda	Obs.	JBO	ZHR
June 26	23h10m	95.16°	3	13	13±8
June 27	07h30m	95.464°	1	28	10±4
June 27	10h20m	95.603°	1	21	66±29
June 27	11h50m	95.662°	1	25	102±41
June 27	19h30m	95.983°	3	40	91±29
June 27	20h10m	95.993°	6	68	66±16
June 27	20h40m	96.014°	6	69	59±14
June 27	21h20m	96.036°	8	97	63±13
June 27	21h50m	96.056°	14	150	50±8
June 27	22h10m	96.072°	11	102	48±10
June 27	22h40m	96.093°	14	155	60±10
June 27	23h20m	96.122°	14	113	53±10
June 28	00h00m	96.144°	14	114	50±9
June 28	00h40m	96.167°	10	81	53±12
June 28	01h00m	96.187°	6	33	39±14
June 28	01h20m	96.199°	2	8	24±17
June 28	12h20m	96.64°	1	0	0
June 29	11h00m	97.53°	6	6	2±2
June 29	21h00m	97.93°	1	0	0

The 1998 event

A considerable amount of 511 magnitude estimates allowed the determination of a population index of the June Bootid meteor shower. We derived r=2.22±0.07 from observations of the period June 27, 19h30m to June 28, 01h30m UT. This population index as well as the average radiant position of alpha=230° and delta=+47° (see below) were used to obtain a profile of the ZHR (Figure 2). Highest rates of roughly 100 occurred between June 27, 12h and 20h UT. Whereas these rates are based on very few observations, the ZHRs of the period June 27, 20h to June 28, 1h30m UT constitute a reliable picture of the activity.

Another surprising fact is the large apparent size of the radiant area. This was reported in the early activity events as well as during the 1998 display. Other meteor showers producing high rates show a well-defined radiant. The analysis of 139 meteor plots by Bojurova, Rashkova and Velkov with the RADIANT software [18] yields a distinct radiant at alpha=230°±2° and delta=+47°±2° (eq. 2000.0), which correspods very well to the average radiant position reported by all other observers. The software corrects each individual meteor for zenithal attraction by assuming a most probable radiant for each meteor according to its direction and speed. The resulting radiant is fairly compact, in contrast to the reports of other observers.

[June Bootids by Denning, 1916]

Figure 3: Analysis of the meteor plots of Denning of the 1916 June Bootid return. Since no meteor velocities are available, simple backward tracings of the paths are drawn and accumulated.

[June Bootids from Bulgaria, 1998]

Figure 4: Analysis of 139 meteor plots recorded by Bojurova and Velkov on June 27-28, 1998. The graph was obtained by the application of the probability method (see [18] for details), which determines an area of radiant probabilities behind every meteor. A pre-atmospheric velocity of 18 km/s was assumed.

It is argued that the large scatter in radiant positions results from the strong zenithal attraction of slow-velocity showers, which varies between 0° (radiant at the zenith) and 12° (radiant elevation 10°). The radiant height decreases from 80° to 40° during the night on mid-northern latitudes, inflating the apparent radiant by 7° automatically.

Upon processing the films, one of the authors (Valentin Velkov) found five photographs of June Bootids. Four of them, situated in a fan-shape within an angle of almost 180°, formed a radiant with coordinates alpha=229.6° and delta=48.1°. They appeared in the interval between 20h35m and 22h10m UT, when the zenith attraction is not very large. Given a pre-atmospheric velocity of 18 km/s, this apparent radiant position corresponds to a geocentric radiant at alpha=225.2° and delta= +48.4°. This is very close to the radiant position derived from a double-station photograph of a June Bootid at alpha=222.9° and delta=+47.6° reported in [19].

Discussion

When the Earth crossed the meteoroids of comet 7P/Pons-Winnecke in 1916, the particles were far behind the comet-298 days. Meteors released from the comet during the perihelion passage in 1915 were substantially disturbed by Jupiter between 1917 and 1919. The closest approach to Jupiter occurred in mid-May 1918 (0.719 AU).

Table 3:Radiants given for the June Bootids as given in historical records as well as in 1998 reports. If the column ``Z'' is tagged, the radiant was corrected for zenithal attraction. Note the large scatter in the positional data.

Date alpha delta Source Equinox Z

1916 Jun 28 203° +53° observer at Birmingham; [20] Olivier (1916) 1900.0?

1916 Jun 28 221° +56° Denning [21], no. 183 1900.0?

1916 Jun 28 231° +54° Denning [21], no. 184 1900.0?

1916 Jun 28 213° +53° Denning [21], no. 185a 1900.0?

1916 Jun 28 223° +41° Denning [21], no. 185 1900.0?

1916 Jun 28 213° +49° Nakamura (in Kronk [9]) 1950.0?

1921 Jun 28 228° +58° Denning [21], no. 186 1900.0?

1921 Jun 28/29 208° +61° Hoffmeister [8]; 12 meteors 1910.0

1927 Jun 26.8 198° +53° 3 observers Tashkent (Sytinskaya [4]) 1927.0 yes

1927 Jun 27 213° +55° Dole (King [16]) 1900.0?

1927 Jun 27.8 198° +54° 4 observers Tashkent (Sytinskaya [4] 1927.0 yes

1927 Jun 28.8 198° +54° 2 observers Tashkent (Sytinskaya [4]) 1927.0 yes

1927 Jun 29.7 200° +54° 2 observers Tashkent (Sytinskaya [4]) 1927.0 yes

1927 Jun 30 218° +60° Dole (King [16]) 1900.0?

1927 Jun 30.7 204° +55° 1 observer Tashkent (Sytinskaya [4]) 1927.0 yes

- Jun 27-30 212° +58° Bakulin [22], no. 18 (visual) 1950.0

- Jun 13-Jul 02 229° +48° Bakulin [22], no. 90 (photographic) 1950.0?

- Jul 01 209° +56° Bakulin [22], no. 52 1950.0?

1942 Jul 06 206° +54° Bakulin [22], no. 29 (telescopic) 1942.0

1944 Jun 24 208° +55° Bakulin [22], no. 30 (telescopic) 1900.0

1987 Jun 27 229° +44° Velkov 1950.0 yes

1998 Jun 27.6 218° +53° report Vodicka and Marsh, radiant position 2000.0 yes

corrected by McNaught (1998, meteorobs)

1998 Jun 27.60 228° +54° Brown and Hocking [23]; radar 2000.0

1998 Jun 27.60 219° +61° Brown and Hocking [23]; radar, second rad. 2000.0

1998 Jun 27.89 222°9 +47°6 Spurny and Borovicka [19]; 2-station photograph 2000.0 yes

1998 Jun 27.9 225° +48° Velkov, 5 photographic meteors 2000.0 yes

1998 Jun 27.9 230° +47° Bojurova, Rashkova, Velkov 2000.0 yes

1998 Jun 27.9 237° +46° Crivello (1998, pers.\ comm.) 2000.0 yes

1998 Jun 27.9 240° +50° Gorelli (1998, IMO News) 2000.0

1998 Jun 27.9 224° +50° Haver (1998, IMO News) 2000.0

1998 Jun 27.9 220° +59° Stomeo (1998, IMO News) 2000.0

Date	alpha	delta	Source	Equinox	Z
1916 Jun 28	203°	+53°	observer at Birmingham; [20] Olivier (1916)	1900.0?
1916 Jun 28	221°	+56°	Denning [21], no. 183	1900.0?
1916 Jun 28	231°	+54°	Denning [21], no. 184	1900.0?
1916 Jun 28	213°	+53°	Denning [21], no. 185a	1900.0?
1916 Jun 28	223°	+41°	Denning [21], no. 185	1900.0?
1916 Jun 28	213°	+49°	Nakamura (in Kronk [9])	1950.0?
1921 Jun 28	228°	+58°	Denning [21], no. 186	1900.0?
1921 Jun 28/29	208°	+61°	Hoffmeister [8]; 12 meteors	1910.0
1927 Jun 26.8	198°	+53°	3 observers Tashkent (Sytinskaya [4])	1927.0	yes
1927 Jun 27	213°	+55°	Dole (King [16])	1900.0?
1927 Jun 27.8	198°	+54°	4 observers Tashkent (Sytinskaya [4]	1927.0	yes
1927 Jun 28.8	198°	+54°	2 observers Tashkent (Sytinskaya [4])	1927.0	yes
1927 Jun 29.7	200°	+54°	2 observers Tashkent (Sytinskaya [4])	1927.0	yes
1927 Jun 30	218°	+60°	Dole (King [16])	1900.0?
1927 Jun 30.7	204°	+55°	1 observer Tashkent (Sytinskaya [4])	1927.0	yes
- Jun 27-30	212°	+58°	Bakulin [22], no. 18 (visual)	1950.0
- Jun 13-Jul 02	229°	+48°	Bakulin [22], no. 90 (photographic)	1950.0?
- Jul 01	209°	+56°	Bakulin [22], no. 52	1950.0?
1942 Jul 06	206°	+54°	Bakulin [22], no. 29 (telescopic)	1942.0
1944 Jun 24	208°	+55°	Bakulin [22], no. 30 (telescopic)	1900.0
1987 Jun 27	229°	+44°	Velkov	1950.0	yes
1998 Jun 27.6	218°	+53°	report Vodicka and Marsh, radiant position	2000.0	yes
			corrected by McNaught (1998, meteorobs)
1998 Jun 27.60	228°	+54°	Brown and Hocking [23]; radar	2000.0
1998 Jun 27.60	219°	+61°	Brown and Hocking [23]; radar, second rad.	2000.0
1998 Jun 27.89	222°9	+47°6	Spurny and Borovicka [19]; 2-station photograph	2000.0	yes
1998 Jun 27.9	225°	+48°	Velkov, 5 photographic meteors	2000.0	yes
1998 Jun 27.9	230°	+47°	Bojurova, Rashkova, Velkov	2000.0	yes
1998 Jun 27.9	237°	+46°	Crivello (1998, pers.\ comm.)	2000.0	yes
1998 Jun 27.9	240°	+50°	Gorelli (1998, IMO News)	2000.0
1998 Jun 27.9	224°	+50°	Haver (1998, IMO News)	2000.0
1998 Jun 27.9	220°	+59°	Stomeo (1998, IMO News)	2000.0

The comet and the particles of each ejection phase are disturbed by Jupiter in a different way. The question whether this effect is the reason for the large scatter of the radiants reported at all occasions, can only be answered after the fully attraction-corrected radiant analysis of original data plus an evolution study of orbital elements of June Bootid meteoroids.
It is certainly a typical feature of short-period cometary meteoroid streams to show an activity behaviour which is decoupled from the orbital motion of the parent body. Perturbations from Jupiter are assumed to be the key mechanism which directs filaments of the stream closer to Earth at certain times. Since it is not the comet's perihelion passage but the encounter conditions with Jupiter which trigger an outburst, filaments ejected at different perihelion passages (being evolved quite differently) will be directed towards the Earth resulting in broad activity profiles and possibly different radiants at each return.
In 1916, the enhanced rates were observed when the comet was far away from the perihelion (298 days). Comet 7P/Pons-Winnecke reached its perihelion on June 21.1, 1927, and high rates were observed for more than two nights. The situation was quite similar in 1921, when the perihelion was passed on June 13.4, but the rates remained low.
Radiant searches among photographic and radar orbits give only weak hints on the existence of a shower. Sekanina [24] associated 4 streams found from radar data with the orbit of 7P/Pons-Winnecke. The most prominent are the ``July Draconids'' (54 orbits) between June 2 and July 19, with an average radiant at alpha=209.8° and delta=+70.7°. Much closer to what we call the June Bootids are the ``Bootid-Draconids'' in Sekanina's list, with a nodal passage on July 2, 1969, and a radiant at alpha=233.7°±3.1° and delta=+52.2°±1.8°. The geocentric velocity is 14.7 km/s, which is accelerated by the Earth's gravity to a pre-atmospheric velocity of 18.3 km/s.
The available literature and archives do not include hints on significant rates of the June Bootids until 1998. It may well be that a short time activity event of a radiant so far in the northern sky was missed due to the short nights at mid-northern latitudes. However, the analyzed returns of the June Bootids show a remarkably long duration, definitely exceeding one night. Nevertheless, it remains most difficult to say whether the few meteors reported over the years are real members of a meteoroid stream associated with 7P/Pons-Winnecke or sporadic meteors which are aligned with the large apparent radiant area by chance.

References

[1] C. Hoffmeister: Die Meteorströme. J.A. Barth, Leipzig, 1948

[2] R. Arlt: The New Working List of Visual Meteor Showers. WGN 23:4, 1995, pp. 104-109

[3] N. Sytinsky: Der Strom der Pons-Winneckiden im Jahre 1927. Astron. Nachr. 232, 1928, pp. 283-286

[4] N. Sytinskaya: The Meteors of Pons-Winnecke's Comet in 1927. Publ. Tashkent Astron. Obs. 1, 1928, pp. 91-99

[5] I. Yamamoto: Photograph of a remarkable meteor. Astrophys. J. 66, 1927, pp. 329-332

[6] W.F. Denning: Meteoric Shower of 1916 June 28. The Observatory 40, 1917, p. 95

[7] W.F. Denning: Remarkable Meteoric Shower on June 28. MNRAS 76, 1916, pp. 740-743

[8] C. Hoffmeister: Die Beobachtungen von Meteoren des Winneckeschen Kometen. Astron. Nachr. 215, 1922, pp. 455-456

[9] G. Kronk: Meteor Showers. A Descriptive Catalog. Enslow Publ., Hillside, 1988

[10] A. Prey: Meteoritenbeobachtung in Prag (Sternwartenturm). Astron. Nachr. 214, 1921, pp. 39-40}

[11] H. Svoboda: Les météores de la com\`ete de Winnecke. Astr. Nachr. 218, 1923, pp. 255-256

[12] A. Jadot: Tableau des étoiles filantes enregistrées pendant les 2 nuits des 28-29 juin et 30-1^er juillet 1921. Ciel et Terre 37 1921, pp. 94-95

[13] W. Heybrock: Beobachtung von Meteoren des Winneckeschen Kometen. Astron. Nachr. 214, 1921, pp. 215-216

[14] I. Yamamoto: Observations in Japan of Meteors probably connected with Pons Winnecke's Comet. The Observatory 45, 1922, pp. 81-83

[15] W.F. Denning, The Observatory 45, 1922, p. 83 (comment)

[16] A. King: Meteor Notes - The Pons-Winnecke shower. The Observatory 51, 1928, p. 25

[17] B.G. Marsden, G.V. Williams: Catalogue of Cometary Orbits, 10th ed., IAU/MPC, 1995

[18] R. Arlt: The Software Radiant. WGN 20 :2, 1992, pp. 62-69

[19] P. Spurny, J. Borovicka: June Bootid Meteors 1998. IAU Circular 6973,July 21, 1998

[20] C. Olivier: The Meteor System of Pons-Winnecke's Comet. MNRAS 77 , 1916, pp. 71-75

[21] W.F. Denning: Radiant Points of Shooting Stars observed at Bristol chiefly from 1912 to 1922 inclusive. MNRAS 84, 1923, pp. 43-57

[22] P.I. Bakulin: Astronomical Calendar, Constant part. Nauka, Moscow, 1973 (in Russian)

[23] P. Brown, W.K. Hocking: June Bootid Meteors 1998. IAU Circular 6966, July 4, 1998

[24] Z. Sekanina: Statistical Model of Meteor Streams. IV. A Study of Radio Streams from the Synoptic Year. Icarus 27, 1976, pp. 265-321

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