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RE: (meteorobs) A-T's discussion
On Wed, 18 Sep 1996, GWG wrote:
> I have a question to ask about the possible periodic nature of the A-T
> meteor stream. If we can assume that there was definitely activity seen
> in 1993 and 1994, and very little, if any activity seen in 1995 or this
> year, this could be evidence that the shower is periodic, if the historical
> research and prediction of a 5.5 or 6 year period by Kronk is considered.
> My question is why then was activity seen in both 1993 and 1994. I realize
> that the 1993 A-T activity was probably greater than that of 1994, but why
> wasn't it only seen one year, like the 1995 Monocerotids, or the 1966 Leonids?
It depends on the distribution of the meteoroids around the orbit. If
the core is extremely concentrated we may observe a very strong
return, possibly with good returns in the years immediately preceding
and following the main outburst from material in the core's halo (e.g.
the Leonids). The Leonid outburst can be thousands of times greater
than in an ordinary year (ignoring the raging debate in WGN Letters).
In the case of the A-Ts the data suggest that its core is more
dispersed; if the core intersects the Earth's orbit in the spring we
could see activity in the halo of the core. If this conjecture is
correct then we may not have seen the best of the A-Ts yet (if the
centre of the core is close to the Earth in mid-September). There may
only be a small factor between `outburst' activity and normal returns
in the case of the A-Ts. So the concentration is spread around at
least 20 per cent of the orbit. This would be easier to explain if I
could make some drawings. A crude analogy using mathematical
parlance, is a cross-section through the Leonid core approximates to
delta-function (spike); whereas the A-T cross-section is extended,
something like a Gaussian. (I know we don't know the distribution's
shape.) I don't think that I've explained this terribly well, but I
hope you get the idea.
The Monocerotid outbursts are due to another phenomenon that Peter
Jenniskens has been able to model (solar reflex motion), and hence
make predictions.
Malcolm
References: