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(meteorobs) More on pi Puppids, 23 April
Hello Adam and others,
I had promised to look for some more info on a possible 1998 pi Puppid
display. The stream is connected to comet P/Grigg-Skjellerup and produced
fine activity outbursts in 1977 and 1982 on April 23. In years inbetween
the perihelion returns of the parent, activity is low (ZHR<=2). But in
1977 and 1982 activity approached that of the eta Aquarids for a short
while (there are some differences in reported peak ZHR's, but it seems
that these must have been 30-50 at least).
Currently, the earth orbit approaches the comet orbit to about 0.01 AU on
April 23. That is close enough for a display, but the comet has undergone
some orbital disturbance from Jupiter in the sixties, and it seems that
dust still not has build up along its entire orbit. Only when the comet
is close (e.g. 1977, 1982), clear activity is noted around closest
passage to the orbit. The orbital period is 5.1 years.
This comet moves in one of those typical 'near comet outburst' orbits in
which perihelion and node almost coincide (e.g. the October Draconids and
1916 June Draconids do the same).
The comet passed perihelion last year, on August 30 1997. Thus, coming
April 23 we will pass the node some 230 days after the comet. In 1997, we
did that some 4 months before the comet. That year, some activity in the
order of 2-3 meteors an hour (with the radiant not too high) reportedly
has been noted by Australian observers. Note: that need certainly not
have been highest rates! An attempt for a coordinated
visual/photographic campaign by Peter Jenniskens of NASA/Ames and some
New Zealand amateurs failed: they were clouded out.
It is very difficult to say if anything will be vissible coming april.
That depends on how far the main dust concentration extends behind the
comet. In his 1993 review paper on possible outbursts for the Smolenice
conference 'meteoroids and their parent bodies', the late Dr.
Kresak judges the prospects for 1998 favourable, and he predicts a possible
activity surge near April 23.5 UT, with an uncertainty of a few hours.
That would favour Australia. Passage of the node takes place around 15:45
UT on April 23. Any outburst (if Any) can be expected to occur within a
few hours on either side of that time. So it is clear, that there might
indeed be a chance for a nice display, but nothing can be said for sure.
Then, the best thing to do is to just keep an eye on it: a good
inscentive for observing!
The stream has a theoretic radiant at RA 107 degrees, declination -45
degrees. It is an evening stream, with the radiant setting (for
Australia) near midnight. Thus, if you observe anything, that will
probably be with low radiant altitudes. The meteors are extremely slow:
19 km/s. When the radiant is very low, this can result in a seeming
upward shift of the radiant position by some degrees due to 'zenith
attraction'.
-Marco Langbroek
Dutch Meteor Society
References: