(meteorobs) Re: 2012 Draconids (about fM)

Jeremie VAUBAILLON vaubaill at imcce.fr
Fri Jan 28 13:30:31 EST 2005


Hello guys,

Thanks a lot for explaning exactly how you do compute your f_M value.

Actually, the f_M factor was introduced by Asher & McNaught to quantify 
the gravitational perturbations induced by the planets to a meteoroid 
stream. So they logically refered to a 1 Rev. trail, without planetary 
perturbation.

When I started my PhD on Leonids, it sounded to me that the problem is 
that everything is always changing (orbit of parent body for example), 
and that planetary perturbations can be so important that after a while 
this f_M factor has no useful meaning. Actually I was right and wrong at 
a time.

Wrong because when a stream is not much perturbed, this is definitely a 
useful tool. During these last months Peter Jenniskens helped me to 
compute "another f_M factor", based on the number of particles at a 
certain delta_a value from that of the comet.
But I was also right, because having a look at very perturbed stream, 
and as I showed at the last Meteoroid 2004 or International Meteor 
Conference, any attempt to refer to another trail is just meaningless.

I think the computation of f_M is of particular difficulty (in the sense 
of "making sense") for short period stream, such as Draconids, because 
their orbit lead them to close encounters with Jupiter, and then, the 
perturbation is very high. It is then not surprising at all that 
slightly different models give completely different f_M value.

Jeremie Vaubaillon

-- 
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* Jeremie VAUBAILLON
* Dept. of Physics & Astronomy
* University of Western Ontario
* London, Ontario
* N6A 3K7
* CANADA
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* URL : www.imcce.fr/~vaubaill/
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