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(meteorobs) WG-PACM Alert: Beta Cygnids Nov. 1-8



Alert from the IAU C-22 Pro-Am Working Group:


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

Peter Jenniskens       
Chairman - IAU C-22 Pro-Amat Working Group
e-mail: peter@max.arc.nasadot gov       


                                              **Beta Cygnids Nov. 1-8** 

Below is another alert to possible unusual meteor activity. Please observe
this event if possible in the hope of documenting a meteor outburst.

On November 3, 1997, the Earth will pass close to the orbit of comet 
103P/Hartley 2. That orbit used to pass just within the Earth's orbit back
in the return of 1991 and now will pass just outside the Earth's orbit. 
At face value, the minimum distance (+0.040 AU) will be too large to
have any reasonable expectation of meteor activity associated with this
comet. However, comet and meteoroids do not change their orbit in the same
manner. There is a chance, perhaps, that the meteoroids 49 days in front of
the comet are less perturbed than the comet itself and intersect the Earth's
orbit. However, there is no indication that we might expect high rates.
Instead, we hope for a recognizable signature of the stream, some level of
activity that can provide information as to how meteoroid streams are 
perturbed when the comet orbit changes strongly.

The Earth will pass closest to the comet's orbit near perihelion on Nov. 3
at 0.9 hours UT (solar longitude 220.681 -J2000) rather
than at the comet's descending node on Nov. 2 at 7.1 hours UT.
Conditions are excellent, with only
a sliver of a Moon early in the evening. Don Yeomans at JPL
calculated an apparent radiant
position at approximately RA = 295.6, DEC = +31.3 degrees (J2000), not far
from beta-Cygnus. That is quite a bit higher in declination than a previous
radiant calculated by Hasegawa for the 1985 orbit: RA = 290, DEC = +7 [4],
illustrating the change in orbit. The present orbit extends
the interval that northern hemisphere observers can view the stream.
The meteors should enter at an apparent velocity of only about 17 km/s.  

What are the chances that there will be a meteor outburst (even if only
one meteor per hour)?
Yeomans calculated that the Earth will lead the comet to this close approach
point by 49 days. That is very little. But the separation distance will
be some 0.04 AU
with the Earth just outside the comet's orbit, which is very large. It will
depend on how the dust in front of the comet is perturbed whether we will
see any meteor activity at all.  

Moreover, calculations by Mark Matney of Johnson Space Center
show that the most recent dust may not have spread far enough
along the comet orbit for Earth to be able to meet it 49 days in front
of the comet. This is not a certain conclusion, because the difference
is only a factor of two in time. However, it is clear that we  
should not put our expectations too high.

Also, the problem is that the time of nearest passage does not need to be the
time that we cross the dust sheet. The comet has
an orbit at a shallow 13.6 degree angle with the ecliptic (was 9.3 degrees
before the disturbance). A small deviation of the main dust sheet relative
to the comet orbit can lead to a significantly different time of the event.

In principle, the window of opportunity stretches from the time of passing
the comet node on November 2 at 07.1h UT, until at least the point of nearest 
passage to the comet orbit on November 3 at 00.9h UT, while probably extending
several days after that until a point in time closer to the node of the
previous orbit (Nov. 8).

The duration of the outburst depends on the thickness of the dust sheet
and the path of the Earth through the stream. If we only account for the
inclination of the orbit, then the duration of the event, the
time between activity levels of 14% of peak
activity, will be of order 5 - 8 hours, based on the thickness of the 
dust sheets responsible
for the Andromedids, iota-Draconids, October Draconids and Puppids, which
are all very similar. It is clear that such relatively short period of
activity coupled with a very uncertain time of maximum needs global
monitoring. 

There may also be some low level activity that
extends over many days. Any meteor activity of slow meteors from the
beta-Cygnid radiant is an interesting clue to learning how meteor streams
are perturbed when the comet orbit is strongly changed.  

The comet itself may reach magnitude +8 
shortly after passing perihelion on December 21. Orbital elements
calculated by Kenji Muraoka, finding charts and
a predicted brightness evolution can be found at the website:
http://www.info.waseda.ac.jp/muroaka/members/seiichi/comet/catalog/0103P/199
7.html


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Distributed by:


James Richardson
Graceville, Florida
richardson@digitalexp.com

Operations Manager / Radiometeor Project Coordinator
American Meteor Society (AMS)
http://www.serve.com/meteors/