(meteorobs) Questions on september radiants

[meteors at eclipse.net]

>>KA>>>
Thank you in advance to all of you that'll take the time
to answer !
First, I read on Gary's Kronk webpages Meteor Showers Online,
that the alpha-Aurigids were probably linked to the comet
Kiess (1911 II), which has a nearly parabolic orbit. Has
anyone found an explanation to explain why outbursts always
occur, even 75 or 83 years after its passage to perihelion ?
How is it possible that a single comet passage give birth
to such a regularly active meteor shower ?

MW>>
The answer appears to be that we aren't where we think we are. Huh?

Yes, Keiss is what is called an Intermediate Long-Period comet, with a
semimajor axis of ~ 185 AU and a period around 2500 years.
So, obviously, the source of the outbursts is not related to the position
of the comet in it's orbit.
It appears that an idea first proposed by Dr Peter Jenniskens over a
decade ago is coming to fruition.
That is that the position of the dust trail and the earth is affected by
the location of the sun and the barycenter of the solar system.
The barycenter is the center of mass of the whole solar system, and is
mostly that of the sun. However the 4 gas giant planets have enough mass
to slightly shift the location within the sun by about 0.1 AU.
The planets contribute to the barycenter location by ~ 49% Jupiter, 27%
Saturn, 8% Uranus, and 15% Neptune.
All the other rubble (including the earth) contributes much less than 1%.

So the orbit of the earth and cometary dust trail is pulled slightly back
and forth by this motion of the center of mass.
The outbursts have occurred when the barycenter has been in generally the
same position. Which happens to be the case this year.
In fact Dr. Jenniskens is predicting an outburst this year at 11:36 UT
Sept 1 +/- 20 minutes.
This would be visible from the West coast of North America, including
Alaska and Hawaii. (Daylight in the east)


>>KA>>
Second, according to the same source, delta-Aurigids (and I
guess, the newly named September Perseids) find maybe their
origin in comet Bradfield (1972 III). The website of the IMO
speaks of a possible complex of streams in Aries-Perseus-Aurigae-
Cassiopae. Can anyone tell me which streams are part of this
complex ? Delta-Aurigids or alpha-Aurigids ? What are the
coordinates of the suspected other showers that have been
observed once by the past, and never recovered since ? Does
anyone know what the source of this complex ? Comet Bradfield
or Kiess ?

MW>>
That association has not been verified in recent investigations.
We should leave the Aurigids (AUR) out of this part, since that stream has
a "known" source as described above.
Jenniskens lists no parent object for the SPE's (September Perseids) and
DAU's (delta Aurigids).
AFAIK, the earlier suggestions of parent objects has not been
verified....we just know that the showers occur.
There's another shower PJ mentions with a parent object, the beta Aurigids
(C 1790 A1 Hershel)

The IMO has split the SPE and DAU into two seperate showers since there is
a distinct lull in activity between them and the continuation of the
radiant position appears to be a coincidence. Perhaps that will change in
the future, should parent objects be found.



KA>>
And my last question for the moment deals with the Antihelion
radiant : what is it really due to ? I thought it was the
particles of the ecliptic that were at its origin ? Is it right ?
In that case, why does it seems to originate from the Antihelia
point ? Shouldn't it be slightly shifted due to the Earth rotation
or revolution around the Sun ? And has anyone ever observed visually
a meteor coming from the Helion source (earthgrazer, I imagine...) ?

MW>>>
The Helion point, being toward the sun would be the daytime showers.
Again, AFAIK, a few earthgrazers have been observed, but I don't have any
reliable data source on that, so will leave that alone for now.

The Antihelion meteors in fact, do not radiate from the exact antihelion
point. Since these are particles near the ecliptic in prograde orbits, the
actual radiant is about 15 degrees east of the precise antihelion point.
If you look at the intersection of objects in orbits of low eccentricity
hitting the earth in prograde orbits, it makes sense, but trying to
explain that without a 3D model in front of you is beyond the words I have
available. Feel free to stop by and I'll show you :>

Wayne