(meteorobs) The Aurigids in 2007: Jenniskens expects a, ZHR of 400+

[Esko Lyytinen]

Joe and others,

Thanks for the moon correction! I have not checked this myself.

This (the true orbital period of the parent comet) is a good question. 
The orbital period is clearly quite uncertain, for several hundred 
years, if not even more

The next is more or less dealt with in the ICARUS paper by Jenniskens 
and Lyytinen. What I write here, may be a little technical, don't know 
if this is easy to follow, maybe not.

To calculate the trail position in a given moment, typically needs the 
parent comet orbit and timing well known back to the ejection.

However, in the case of long period, the one revolution "makes it shape" 
practically while coming back (after one revolution) in the planetary 
distances.
And because the location was known for one moment (i.e. the parent 
comet) the rest can be calculated. And the trail course is only weakly 
dependent of the true orbital period, IF this is long, at least a few 
hundred years, like the Lyrids have.

With the same principle, the aMo 1-rev trail can be calculated even 
though the parent comet is unknown!

(Even with long period comets, the 2-revolution trail etc. would need 
the comet orbit well known back to the time of ejection. But with long 
periods, the trails other than 1-rev will get very well mixed and will 
practically not give any outburts. At the Lyrids ( few hundred years) 
period range, there might be some 2-revolution trail weak outbursts but 
these can not be predicted, since the comet orbit is not well known even 
one revoluton back.)

With the Aurigids, the previous outbursts tended to happen a little 
earlier (from about 15 minutes to one hour) than calculated, when 
starting from the parent comet orbital elements (Marsden).
I have tested with "forcing" the parent comet orbit with a little 
shorter orbital period into reconstructed positions (from the Marsden 
elements).
This would somewhat shift the comet orbit node and explain some of the 
anomaly. So I think that the true orbital period of the parent comet was 
probably of shorter period than derived, maybe between 1000 and 1500 
years. Peter and Jeremie may have other thoughts on this (particulars of 
ejection?) and in this orbital period  explanation, some "anomaly" of 
timing will in any case be left in the 1994 outburst, by about 40 minutes.

So in here, the true orbital period mostly affects trough the 
uncertainties of other orbital element and correlations (or 
dependencies) of these with the orbital period, than the direct effect 
of changing only the period in the modeling.

Doing the (parent comet orbit) fit into shorter orbital period affects 
(in this case) the timing of predictions, but practically not at all to 
the miss-distance.

(
Then the orbital period in the sense of how long it will take (or did 
take) to go one orbit, may differ quite a lot from the one calculated 
from the oscillating elements near perihelion (like Joe did). Looking 
quickly my earlier calculations would give the time to complete the 
latest orbit as starting from the very same e-value given by Joe would 
be more close to 1900 years (i.e. close to two thousand years). Because 
the planet masses will also pull the comet (when far away) towards the 
Sun, the osculating orbital period derived near perihelion is typically 
more long than the true time of orbital revolution, like in this case, 
but it can also be the other way of course, with some more specific 
planetary perturbations..
)

This is not related to the questions that I reply, but taking the more 
exact miss-distances (of these latest modelings with orbital period 
shift, by me), and some properties from the Leonids modell, I would 
predict the 2007 ZHR to be a little higher than say in 1994 maybe 1.5 
times that!

Esko

 >>>

In a message dated 8/19/06 11:26:15 AM Eastern Daylight Time,
verfl.meteors at seznam.cz writes:

<<  on http://astro.cas.cz/nuncius/ you can find the IAU's GA daily 
newspaper
(okay, that's a bit of  self-propagation, i'm one of the editors:) and in
the 6th issue down there look on the first page - there is an article from
Dr. Jenniskens and Dr. Vaubaillon, approximately equal to Dr. Jenniskens'
yesterday's annoucement.  He also speaks there about his coming book about
meteor showers which shall be available somewhere in september, I think, and
which can probably provide more information on the topic.   >>

Jan --

A very interesting article, with very exciting prospects! 

I would, however, like to point out a correction, followed by a question,
which perhaps Dr. Jenniskens, Jeremie Vaubaillon or Esko Lyytinen might 
be able
to answer. 

First . . . the correction.  The article states that next year's Aurigid
shower will take place three days before a Full Moon occuring @ 02:32 UT on
September 4.  In reality, the shower will peak nearly four days AFTER a 
Full Moon
occurring @10:35 UT on August 28.

As for the question . . . the orbital period being quoted for Comet 
Kiess is
given as ~2,000-years.  However, most reference books (such as Gary Kronk's
Comets -- A Descriptive Catalog) indicate that the period is closer to 
2,500
years.  I plugged the orbital elements for comet Kiess into an orbital 
simulator
on my hard drive (with e = 0.996296) and my computer spit out an orbital
period of 2508.55 years.

Then again . . . what's ~500 years among friends?
 :)
-- joe rao