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Re: (meteorobs) Bradfields



On Mon, 3 Mar 2003, Lew Gramer wrote:
> I am far from completely familiar with the professional literature,
> but I think this is the first time I have heard of any correlation
> between particle ejection velocities and likelihood of fireballs!
> 
> What is the theoretical mechanism for this assumed correlation?

Basically, more massive particles tend to be ejected at lower velocities
as they require a greater force to to propel them to the same velocity as
smaller particles.

> Is it established by any observations?

Yes, the 1998 Leonids had many fireballs and low "r" whereas the those
later Leonid dust trails with higher da0 had fainter meteors and higher
"r".  After correction for solar radiation pressure, da0 (or rather |da0|)
is directly correlated to ejection velocity, hence particle mass hence
meteor brightness.  Note that that encounters at greater re-rd tend to
produce fainter meteors as the effect of srp for ejection away from
perihelion segregates particles by mass.

I think this was dealt with in our various Leonid papers.

> And does it hold equally well regardless of variations parent-body
> composition, density or orbit?

I'd assume so.

Note that when I refer here to "ejection velocity" I'm referring only to
the value for ejection along the comet's direction of motion.  To produce
an orbit of a specific orbital period (or semi-major axis "a" or of
a a specific "da0"), one needs only to have a specific total
heliocentric velocity at the point of ejection.  Particles can potentially
be ejected in any direction and end up with the correct orbital period, if
their ejection velocity vector, when added to the comet's heliocentric
velocity vector (a vector is a speed and the direction it is moving in)
equals that value.  The definition of the dust trail center in the David's 
model of a dust trail is for the path of dust ejected along the comet's
motion.

Cheers, Rob

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