(meteorobs) Re: 2012 Draconids (about fM)
Mikhail Maslov
ast0 at mail.ru
Fri Jan 28 21:16:13 EST 2005
Hello, Jeremie and all
I'd like to add, that I use different definition of fM (therefore the
question of disignation arose). Our fMs (with Mikiya Sato) are
completely different mainly because they are different by nature, not only
due to model distinctions. And that's the reason for me to use other
designation (such as fM(fNP)).
I understand the idea of original fM, but I don't understand why to
use these relative measures. We can easily estimate distances between
particles along the stream without using non-comparable measures.
Also, in Lyytinen-van Flanderns' model for Leonids ZHRs determination
these ZHRs are in direct proportion to fM, this suggest the latter to
be an absolute, not relative measure.
Best regards, Mikhail Maslov
JV> Thanks a lot for explaning exactly how you do compute your f_M value.
JV> Actually, the f_M factor was introduced by Asher & McNaught to quantify
JV> the gravitational perturbations induced by the planets to a meteoroid
JV> stream. So they logically refered to a 1 Rev. trail, without planetary
JV> perturbation.
JV> When I started my PhD on Leonids, it sounded to me that the problem is
JV> that everything is always changing (orbit of parent body for example),
JV> and that planetary perturbations can be so important that after a while
JV> this f_M factor has no useful meaning. Actually I was right and wrong at
JV> a time.
JV> Wrong because when a stream is not much perturbed, this is definitely a
JV> useful tool. During these last months Peter Jenniskens helped me to
JV> compute "another f_M factor", based on the number of particles at a
JV> certain delta_a value from that of the comet.
JV> But I was also right, because having a look at very perturbed stream,
JV> and as I showed at the last Meteoroid 2004 or International Meteor
JV> Conference, any attempt to refer to another trail is just meaningless.
JV> I think the computation of f_M is of particular difficulty (in the sense
JV> of "making sense") for short period stream, such as Draconids, because
JV> their orbit lead them to close encounters with Jupiter, and then, the
JV> perturbation is very high. It is then not surprising at all that
JV> slightly different models give completely different f_M value.
JV> Jeremie Vaubaillon
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