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(meteorobs) QUADRANTID excerpt from "CCNet 7/2002 - 10 January 2002"


I'm working backward by date, through my Inbox! Can you all tell? :)

Lew Gramer


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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 7/2002 - 10 January 2002
Date: Thu, 10 Jan 2002 13:10:53 -0000


CCNet 7/2002 - 10 January 2002
-----------------------------

[...]

(11) QUADRANTIDS DEBATE
     Marco Langbroek <m.langbroek@rulpre.leidenunivdot nl>

[...]

===================

(11) QUADRANTIDS DEBATE

>From Marco Langbroek <m.langbroek@rulpre.leidenunivdot nl>

Dear Benny,

In CCNet 5, Duncan Steel replies to my comment in CCNet 4 about the age of
the Quadrantid shower. In this, he appears to ignore the true content of our
paper in Astronomy & Astrophysics (A&A 327 (1997), 1242-1252).

The central argument of our paper is that the observed dispersion in orbital
elements (i.e. inclination, perihelion and aphelion distance) for meteoroids
in the Quadrantid shower is very small. It is too small, and the orbital set
itself too structured, for the shower to have undergone the evolutionary
trajectory which the models that link the shower to comet Machholz imply.
Our estimate of 500 years at best as an age for the Quadrantids, is based on
a direct comparison of the observed dispersion in the shower to the
dispersion over time given by the model techniques that couple it to
Machholz. Thus, if our assumptions are wrong (Steel's argument), then so are
the assumptions behind the very models which Steel defends. If the models
would be correct, then the observed radiant area and dispersion in orbital
elements of Quadrantid meteors should have been wider than they are in
reality, and they should not show the structuring which we observed.

The dispersion in the Quadrantid orbits and radiants we gathered is small by
any standard. It is small for example when compared to other annual streams
like the Perseids or Geminids. Moreover, the data are structured: they show
a number of interesting correlations between velocity and mass on the one
hand, and radiant structure and orbital elements on the other hand. Taken
all together, the suggestion really is that the stream is young, as we point
out in our paper.

Steel wrote:
"Here I simply mention that rejection of the hypothesis that 96P/Machholz 1
is the parent for the Quadrantids implies that its fitting against not only
the Quadrantids but also the other showers that the stream produces is a
matter of chance, the likelihood of which is very slim. This would offend
against William of Ockham (who of course is not infallible)."

In answer to this, I want to point out that of the several (6, 8?) predicted
theoretical showers from comet Machholz, according to Jones & Jones (to
which Steel refers) only 3 (Quadrantids, Arietids and delta Aquarids) appear
to match observed showers. Of these 3, the match with one (the Arietids) is
problematic, as Jones & Jones point out, leaving only the delta Aquarids and
Quadrantids. We in turn question the relation with the Quadrantids. This
leaves one stream (Aquarids) from the initial lot, with a second (Arietids)
problematic. Will William of Ockham please stand up?!

Finally, for the benefit of the CCNet reader, I want to point out that the
Quadrantid orbits of "this DMS group" (quod Steel) are not only the most
accurate to date, but also one of the largest samples available. Before we
added our 35 photographic and 29 video orbits, there were only 18 high
accuracy Quadrantid orbits in the IAU photographic meteor database (and some
100 less accurate). Our dataset showed that what was thought to represent
true intrinsic dispersal in the shower meteoroid orbits, in reality is due
to unacknowledged inaccuracies in the orbital determinations, the results of
our large set of orbits being much tighter constrained in radiant positions
and orbital elements than the older sets of photographic orbits.

Kind regards,

Marco Langbroek
Dutch Meteor Society (DMS)

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