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(meteorobs) Re: Meteoroid Size

>  Could this unexpectedly high figure for cometary showers be the result of a
>  relationship between particle size and density in cometary meteoroid streams?
> 
> In other words, are "normal" brighter meteors far more dense than "normal"
>  less bright ones for some reason? Thinking about the "dirty snowball" model,

There is relation between magnitude of the meteor and it's density, by the
same argument I gave you for the relation to the mass.

You remember that energy transfered from atmosphere to the meteoroid (and
thus made available for radiation) is proportional to the surface area of
the particle. And in previous messge I told you that S~M^2/3. I just
didn't want to involve too many quantities at that time, but we need them
now: S = A (M/rho)^2/3 ! Here rho is density of meteoroid, and A is form
factor, for sphere A=1.21.

Thus obviously, I ~ v^5 * (M/rho)^2/3, or if you want

mag ~ -2.5(5*log v + 2/3log M - 2/3log(rho))

(btw. I forgot the '-' sign in front of 2.5 last time, as you've probably
noticed it.)

If you take two meteoroids of same mass, and same velocity, you get

m2-m1 = 2.5 * 2/3 log(rho2/rho1)

For stony and iron particle this may be smth. like 1/2 mag. For icy
congragate of stony prtcls, and iron meteoroid, probably more than 1mag,
less dense ones being the brighter.

(Of course, here I neglected (significant) difference between various
coeficients for these two particles...however, I think that this would
only _increase_ difference in magnitudes.)

In brief, density matters, and it's not surprising.

But, please, don't conclude that all 'comet' meteor are brighter than
'asteroid' ones. There is important difference in origin and evolution of
these showers, resulting in differences in mass factor, and therefore
population index (I hope you all know what is it). The only conclusion I
would draw here (in terms of 'average' meteors) is that for the same
initial conditions (mass, velocity...) less dense particle would appear
brighter. 

Note that what REALLY matters here is surface area (S) of the particle,
and both M and rho enter through S. But, even if you had two particles of
the same radius and velocities (and different densities => masses), their
magnitudes would be different due to the coefficients in theory, favoring
less dense particle to be brighter. (Which makes sense - for stony/icy
particles less energy is spent on ablation => melted material
-responsible for radiation- will be available at higher rate => more
radiation.)

As I see that there is significant interest in this matter, I'll try to
TEX the basic equations of the single body theory and make thema available
on the web during the weekend. (By now I realized that there's no generaly
available literature in English about this topic...) I can't promise I'll
do it, but I'll really give my best.

Best regards,

(comrade ;> ) Vladimir
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