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(meteorobs) A-T's discussion
I am still waiting for plots and other observations of the activity of the
A-T's, but I agree with everyone else that activity was virtually
nonexistent. I have no information to really offer here, but just wanted to
change the subject line and comment on recent discussions.
I fully agree with Malcolm that the population of the A-T's seem
predominantly faint and that observing fields closer to the radiant would
increase an observer's chance of seeing such meteors. I have been informed
by two separate people that an article in WGN in recent years suggested
facing the radiants of minor radiants in order to improve the chances of
seeing stream members. I have not looked through my many years of WGN to
get the exact volume and issue as yet.
Malcolm's question of "Can't dispersive effects in older streams make the
Earth pass through only the part of the stream devoid of larger
meteoroids?" is valid and likely for the A-T's, but opens up some
interesting new problems.
All streams will experience separation effects, with age and planetary
perturbations playing important roles. But this brings up another curiosity
about the A-T's. The lack of large numbers of bright members indicate two
possibilities: the parent body did not produce large particles or the
stream is old enough for a separation to take place. The former possibility
seems unreasonable and has no precedent, so the latter is the more likely.
Now for a new problem. If, as the historical data seems to suggest, this
stream reaches a noticeable maximum every 5.5 to 6 years, this might
contradict the "old" stream scenario. The reasons for a periodic increase
in meteor activity is usually attributed to either an active parent body or
a recently defunct parent body. One implies that material is still being
shed into the stream, while the other implies that, although the parent no
longer releases dust into the stream, the knot of material surrounding the
parent body has not had enough time to disperse throughout the stream. As
we see with the Perseids and Leonids, we will usually experience a
signicant increase in activity when the parent comet is within the inner
solar system, but when we look at the Geminids we see a rather homogenous
stream with no significant variations during maximum from one year to the
next. The Perseids and Leonids have active comets, while the Geminids have
a dead comet. So, if the knot of material is relatively new, why do we have
an apparent lack of large particles? The only likely scenario is that Earth
is not plowing square into this stream, but catching the edge. Since the
separation effect starts as soon as dust production begins, we could be
collecting mostly small particles and missing the larger ones. These
particles would not be recently released particles, but possibly some of
the oldest ones existing within the stream.
This all sounds great, right? But how about a new problem. If we are
currently catching the oldest particles to be released within the A-T
stream, then, with an orbital period of possibly 5.5 to 6 years, they
should have had plenty of time to have spread completely around the orbit.
Malcolm did admit that he could only poorly cover the A-T watch because of
bad weather this year, but what he did get was so weak that it does not
seem to support the possibility that the faint meteors have completely
spread around the orbit. I can think of some additional possibilities to
explain this, but I get the feeling that I could go on and on here, and
since most of this is conjecture, discussion beyond this point would serve
no real purpose at this time.
We need further observations--both visual and telescopic. I really do not
expect much visual activity from this stream next year (although we should
certainly try), but I think the period of 1998 to 2000 could be interesting
in that it could confirm or dispel the theory that the stream is periodic.
If we assume that faint particles have spread throughout the stream,
telescopic and especially video observations would be most important during
the next few years.
Gary
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