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Re: (meteorobs) Whatever happened to 'r'? (Brightness predictions for Leonids)
[Editor's Note: Apologies for this late follow-up. Esko was not
able to post this himself back in October - and I missed it when
his posts "bounced"! :( Clear skies, -Your 'meteorobs' Santa]
We haven't made any real population index model.
To try to do this theoretically, there are very many difficulties, not the
least, the human observability of different brightness meteors (and because
as Rob McNaught had pointed out, the population index is dependent of
magnitude).
But some empirical treatment could be made.
According to a quick comparison with the 2001 r-values, I would expect the
(visually derived) population index of the 4-rev (during maximum) to be
about 2.5 and that of the 7-rev encounter about 2.2. Maybe the moonlight
will also affect this, because the derivation of this will be based on
brighter meteors than in 2001.
If derived like the IMO 'regression line method' in 1999:
http://www.imodot net/articles/shower/leo99.html
somewhat smaller (maybe smaller by about 0.3) values would probably be
reached.
On the background, the 5 and 6-rev trails may give around (ZHR) 100 to 200,
if you consider these background. We have no estimations from the older
trails. Actually I haven't the trail data here in my work now, to possibly
find some producing weak background. I expect some unmodelled (or modelled,
but considered to weak to give a prediction) old trails to give something
above the normal yearly background.
Hope, this will give some help; Esko
>>> Lew Gramer wrote:
There are Leonid "ZHR" predictions lying pretty thick
on the ground as this November approaches... But I've
not heard enough predictions for how BRIGHT either of
the two predicted storm peaks may be! ...
Estimates of 'r' are probably available in actual publ-
ished papers from Mssrs. Jenniskens, Asher & McNaught,
van Flandern & Lyytinen, Vaubaillon, et al. However, a
quick scan of the various websites we collected at:
http://www.meteorobs.org/storms.html
produced no information on the 'r' factors assumed by
any of these predictions.
Would the researchers themselves care to comment - or
has anyone done a Website summarizing this information?
I for one would love to have an idea how badly we can
expect moonlight to affect observable rates this year,
before I embark on my FIVE public talks next month! :)
(Technical note, for folks who like technical notes:
The 'r' is a number which essentially describes how
the magnitudes of meteors in a given shower will be
distributed: an 'r' of 2 means that there should be
about twice as many meteors of magnitude 3 [fainter]
as of magnitude 2 [brighter], twice as many mag. 2s
as there are mag 1s, etc... So the LOWER the 'r' is,
the BRIGHTER the meteor shower is predicted to be!
And note that since brightness has a relationship to
the relative mass of meteors in the same shower, 'r'
is also a number describing the *mass distribution*
of particles in that shower's meteoroid stream...)
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