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IMCCE Meteor Showers - Method

• How to make the ephemerids of a meteor shower ?

Several methods were developped to do meteor showers forecastings. The first at doing it the correct way were Kondrat'eva and Reznikov (1985), independently followed by McNaught and Asher in 1999. During the Leonids meteor storm period, lots of work were done about meteoroids stream in general; see e.g. Brown and Jones 1998. It basically consist of a numerical simulation of the trajectory of the meteoroids ejected by a comet in the Solar System. These authors looked at the conditions recquired for a particle to reach the Earth around the time of the shower. Lyytinen and Van Flandern (2000) considered the satellite model of a comet and modelled the non-gravitational forces as Ai coefficients. The McNaught and Asher's method (or some similar to it) are now used by some amators with success (see e.g. The 2004 June Bootid meteor shower). The problem is that the level of the shower is poorly know in general. Lyytinen and Van Flandern have had better results in this field. Finally, IMO provides some general predictions, from the past observations. A description of the showers was done by P. Jenniskens (see also his web site).

• Method developped at IMCCE

J. Vaubaillon and F. Colas in collaboration with L. Jorda developped a model that takes into accounts the physical processes involved in the ejection of the metoroids by a cometary nucleus. The model of ejection developped by Crifo and Rodionov 1997 was used to simulate the generation of the meteoroids. We consider only the water, and so the ejection is supposed to occur as soon as the nucleus reaches a heliocentric distance less than 3 au. Particles are ejected in the sunlitt hemisphere. Then their trajectory is followed, taking into account the gravitation of the Sun, the 9 planets and the Moon. Non-gravitational forces are included: radiation pressure and the Poynting-Robertson effect. A space criterion examines if the meteoroids are approaching the Earth (or any other choosen planet). In the case of the Earth, the nodes close to the planet are considered as potential intersepting the planet. Then a further analysis decides if tey really are or not. That is how all the graphs are created, and how the time of maximum is computed. The level of the shower is computed from the activity of the comet, measured by the [Afrho] parameter. A statistical weight is set to each simulated particle. It represents the real number of particles the comet is supposed to have ejected in the same conditions as the simulated one. The numerical simulations were done on 5 to 50 parallel processors located at CINES. Each typical run of a trail involves 5 bins of size, containing 10000 to 50000 particles each. A full numerical simulation of a meteor shower considers more than a million of particles and takes several hours to several days to be run. The application to the Leonids showed this method works well.

• How much can we rely on the preditions?
The methods mentioned above generally works very well for "young" trails (<10 revolutions old). The best examples were given with the Leonids between 1999 and 2002. Now the old trails are usually spread out in the Solar system and if an encounter is found with the Earth the level is generally low. However, some studies have shown that the planetary perturbations can locally enhance the spatial density of meteoroids, so outburst can also be caused by the old trails. See in particular Asher et al. (1999) and Vaubaillon and Colas (2005). One of the major uncertainty comes from the poor knowledge of the past orbit of the parent body. This is also why observations are very important, since they can provide some constraints on a path of a comet, maybe several hundreds years ago.
• Application: ephemerides of the meteor showers

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