June Bootids 2006 - prediction of activity
List of predictions
Introduction
Meteor shower of the comet 7P is known for quite a long time, although his activity was observed only on a few occasions. The first time it happened in 1916, when June Bootids gave a strong outburst of several hundred meteors per hour. The next ones were a weak enhancement in 1921 (10-20 meteors per hour) and a stronger peak in 1927 (200-300 meteors per hour). After that significant activity of the shower wasn't observed during more than 70 years - the next outburst with ZHR up to 100 meteors occured on 27 June 1998, and the most recent enhancement happened in 2004 (ąstronomy amateurs Sergey Shanov and Sergey Dubrovsky played a very important role in predicting it). Its ZHR was about 30 meteors on 23-24 June.
Nowadays perihelion distance of 7P is about 1.25 AU. It is very far from the Earth orbit, so the fresh comet material, ejected during the recent comet returns, can't be the cause of two last shower enhancements. Computations made by Sergey Shanov and other researchers showed that both in 2004 and 1998 activity was caused by old comet trails, ejected in 19 centure. Some parts of these trails became resonant 2:1 with Jupiter, it allowed them to remain quite regular.
The vast majority of June Bootids outbursts is traced with the modelling very good. Particles ejected by the comet form lengthy trails. One of the reasons is radiation pressure force, which acts parallel with gravitational force. The latter is dependent on a particle mass, i.e. it is proportional to the third power of particle radius. The outcrying radiation pressuse is defined by the second power of particle radius. So far the influence of radiation pressure is the more the less is size of a particle. Its action is equivalent to the diminishing of gravitational constant G. So it increases the orbital period of particles, and the tinier a particle is, the more it is continuously retarded from larger particles after their ejection from the comet. This process therefore leads to the formation of lengthy comet trails.
Meteor modelling is done through computation of orbital evolution of particles ejected by the comet with different velocities in directions tangential to the comet trajectory at the moment of perihelion. In the reality, of course, particles are ejected not only at the point of perihelion, but also during several months around it. However, comets are in perihelion part of their orbits during quite a little time comparing to their overall orbital period and main perturbations happen around their aphelions, so when comets are closer to the Sun newly ejected particles are moving very close to them in a compact dust cloud. This is the reason we can take that cloud as completely ejected at the point of perihelion, it doesn't virtualy influence the results of computations.
Speaking of directions in which particles are ejected we can say that, again, in the reality they are ejected far not only in tangential directions, but in all possible ones. However, ejection velocities (from 0 to 100 m/s, and the overwhelming majority of real ejections - from 0 to 20 m/s) are negligibly small comparing to the own comet velocity (from 30 to 40 km/s) near the Earth's orbit), ejected particles have only slightly changed orbits and don't "fly away in all directions". Radial part of ejection velocity defines only thickness of a trail, which usually reaches several hundreds thousands kilometers. The shape of the trail is defined by tangential part of ejection velocity.
And the last. Non-gravitational forces are often not taken into consideration in meteor calculations, as is in our case. However, some of them, say, radiation pressure, can be considered indirectly. As far as this kind of force works as diminishing of gravitational constant G, this is equivalent to increase of ejection velocity which could be easily accounted in the model. So this non-gravitational force, as many others doesn't change the configuration of trails, but leads to shifting of particles with different masses along them.
As spoken previously, June Bootid trails modelling allowed to prepare very good predictions of shower activity in the previous years. More serious problem is prediction of outburst intensity - how strong the maximum could be. For such predictions special empirical models were elaborated (the single possible way in this case) but as before for their improvement new observations are very necessary.
The results obtained by the Author for the June Bootids 2006 using the modelling of particles ejected by the comet 7P Pons-Winnecke are presented below. Main characteristics of computations are also described.
Computation characteristics
I wish to introduce the results of June Bootid meteor stream simulation aimed to the prediction of shower activity in 2006. The simulation was made for the trails of latest 48 revolutions, i.e, from the 1720 trail. The Author used the program "Comet's Dust 2.0" by S. Shanov and S. Dubrovsky to calculate orbital elements of ejected meteor particles. To estimate expected ZHRs for different encounters the model described in [4] was used with some Author's alterations made in order to adopt the model for ejection velocity (v) instead of da0 (difference in a-semimajor axis) and to turn the model from the Leonid stream (for which it was originally created) to the June Bootids. The computation considered only gravitational forces, however, the results are on the whole in good accordance with these of other researchers. The prediction includes all encounters found within interval +/-0.007 a.u. The following parts of trails were computed: the first 15 rev. trails for ejection velocities [-50;100] m/s, 16-30 rev. trails - [-30;50] m/s, older than 30 rev. trails - [-20;30].
Results
The Fig. 1 below presents the distribution of 7P dust trails in the vicinity of the Earth's orbit within the period of 24.03.2006 - 10.01.2006. The vertical axis shows the minimal distance between trails particles and the Earth's orbit. So far the Fig. 1 shows the moments of passing minimal distances to the Earth's orbit and these distances themselves for various trails and particles. The central vertical line corresponds to 25 June 2006.
Meteor shower of the comet 7P is known for quite a long time, although his activity was observed only on a few occasions. The first time it happened in 1916, when June Bootids gave a strong outburst of several hundred meteors per hour. The next ones were a weak enhancement in 1921 (10-20 meteors per hour) and a stronger peak in 1927 (200-300 meteors per hour). After that significant activity of the shower wasn't observed during more than 70 years - the next outburst with ZHR up to 100 meteors occured on 27 June 1998, and the most recent enhancement happened in 2004 (ąstronomy amateurs Sergey Shanov and Sergey Dubrovsky played a very important role in predicting it). Its ZHR was about 30 meteors on 23-24 June.
Nowadays perihelion distance of 7P is about 1.25 AU. It is very far from the Earth orbit, so the fresh comet material, ejected during the recent comet returns, can't be the cause of two last shower enhancements. Computations made by Sergey Shanov and other researchers showed that both in 2004 and 1998 activity was caused by old comet trails, ejected in 19 centure. Some parts of these trails became resonant 2:1 with Jupiter, it allowed them to remain quite regular.
The vast majority of June Bootids outbursts is traced with the modelling very good. Particles ejected by the comet form lengthy trails. One of the reasons is radiation pressure force, which acts parallel with gravitational force. The latter is dependent on a particle mass, i.e. it is proportional to the third power of particle radius. The outcrying radiation pressuse is defined by the second power of particle radius. So far the influence of radiation pressure is the more the less is size of a particle. Its action is equivalent to the diminishing of gravitational constant G. So it increases the orbital period of particles, and the tinier a particle is, the more it is continuously retarded from larger particles after their ejection from the comet. This process therefore leads to the formation of lengthy comet trails.
Meteor modelling is done through computation of orbital evolution of particles ejected by the comet with different velocities in directions tangential to the comet trajectory at the moment of perihelion. In the reality, of course, particles are ejected not only at the point of perihelion, but also during several months around it. However, comets are in perihelion part of their orbits during quite a little time comparing to their overall orbital period and main perturbations happen around their aphelions, so when comets are closer to the Sun newly ejected particles are moving very close to them in a compact dust cloud. This is the reason we can take that cloud as completely ejected at the point of perihelion, it doesn't virtualy influence the results of computations.
Speaking of directions in which particles are ejected we can say that, again, in the reality they are ejected far not only in tangential directions, but in all possible ones. However, ejection velocities (from 0 to 100 m/s, and the overwhelming majority of real ejections - from 0 to 20 m/s) are negligibly small comparing to the own comet velocity (from 30 to 40 km/s) near the Earth's orbit), ejected particles have only slightly changed orbits and don't "fly away in all directions". Radial part of ejection velocity defines only thickness of a trail, which usually reaches several hundreds thousands kilometers. The shape of the trail is defined by tangential part of ejection velocity.
And the last. Non-gravitational forces are often not taken into consideration in meteor calculations, as is in our case. However, some of them, say, radiation pressure, can be considered indirectly. As far as this kind of force works as diminishing of gravitational constant G, this is equivalent to increase of ejection velocity which could be easily accounted in the model. So this non-gravitational force, as many others doesn't change the configuration of trails, but leads to shifting of particles with different masses along them.
As spoken previously, June Bootid trails modelling allowed to prepare very good predictions of shower activity in the previous years. More serious problem is prediction of outburst intensity - how strong the maximum could be. For such predictions special empirical models were elaborated (the single possible way in this case) but as before for their improvement new observations are very necessary.
The results obtained by the Author for the June Bootids 2006 using the modelling of particles ejected by the comet 7P Pons-Winnecke are presented below. Main characteristics of computations are also described.
Computation characteristics
I wish to introduce the results of June Bootid meteor stream simulation aimed to the prediction of shower activity in 2006. The simulation was made for the trails of latest 48 revolutions, i.e, from the 1720 trail. The Author used the program "Comet's Dust 2.0" by S. Shanov and S. Dubrovsky to calculate orbital elements of ejected meteor particles. To estimate expected ZHRs for different encounters the model described in [4] was used with some Author's alterations made in order to adopt the model for ejection velocity (v) instead of da0 (difference in a-semimajor axis) and to turn the model from the Leonid stream (for which it was originally created) to the June Bootids. The computation considered only gravitational forces, however, the results are on the whole in good accordance with these of other researchers. The prediction includes all encounters found within interval +/-0.007 a.u. The following parts of trails were computed: the first 15 rev. trails for ejection velocities [-50;100] m/s, 16-30 rev. trails - [-30;50] m/s, older than 30 rev. trails - [-20;30].
Results
The Fig. 1 below presents the distribution of 7P dust trails in the vicinity of the Earth's orbit within the period of 24.03.2006 - 10.01.2006. The vertical axis shows the minimal distance between trails particles and the Earth's orbit. So far the Fig. 1 shows the moments of passing minimal distances to the Earth's orbit and these distances themselves for various trails and particles. The central vertical line corresponds to 25 June 2006.
Fig. 1. Space-temporal projection of June Bootid trails parts onto their minimal distance passages (for each regular part of a trail the year of its formation and the number of revolutions are shown)
We can see, that this year there are only scattered strongly perturbed particles from trails of 18 century in vicinity of the Earth orbit. They are presented by scattered points on the Fig 1. These trais are of 38-50 revolotions old. This means, that June Bootids activity is not expected in 2006 and most probably this year will become one of many others, in which June Bootids were totally absent.
The new Moon on June 25 gives excellent conditions for June Bootids 2006 observation. We'd like to specially note, that even despite the negative prediction of stream activity, its observations are very important. As known, a negative result is also a meaningful result, which could confirm the prediction. And, on the other hand, the prediction could not consider all the finest fiatures of stream dinamics, so unexpected activity is still possible - from older, not computed trails or due to the possible imperfectness of the model.
Conclusions
In 2006 June Bootids activity is expected to be absent. The Moon will be around new phase during the period of the shower activity, so there are good conditions to confirm or disprove the negative prediction.
References
1. "Comet's dust 2.0" program by S. Shanov and S. Dubrovsky. [Used for orbital computations.]
2. Information from Gary W. Kronk's page http://www.maa.agleia.de
3. IMO Meteor Shower Calendar 2006 http://www.imo.net/calendar/russian/2006/spring.
4. Lyytinen E, van Flandern T. "Predicting the strength of Leonid outbursts", 2000, Icarus, P. 158-160.
The new Moon on June 25 gives excellent conditions for June Bootids 2006 observation. We'd like to specially note, that even despite the negative prediction of stream activity, its observations are very important. As known, a negative result is also a meaningful result, which could confirm the prediction. And, on the other hand, the prediction could not consider all the finest fiatures of stream dinamics, so unexpected activity is still possible - from older, not computed trails or due to the possible imperfectness of the model.
Conclusions
In 2006 June Bootids activity is expected to be absent. The Moon will be around new phase during the period of the shower activity, so there are good conditions to confirm or disprove the negative prediction.
References
1. "Comet's dust 2.0" program by S. Shanov and S. Dubrovsky. [Used for orbital computations.]
2. Information from Gary W. Kronk's page http://www.maa.agleia.de
3. IMO Meteor Shower Calendar 2006 http://www.imo.net/calendar/russian/2006/spring.
4. Lyytinen E, van Flandern T. "Predicting the strength of Leonid outbursts", 2000, Icarus, P. 158-160.