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RE: (meteorobs) Perseid stream spread (was: NAMN Notes: July 1999)
Sirko said more or less what I was going to write until I felt sick
last night. Ejection velocities are the main difference. There are
various dispersive forces, not just radiation pressure. Most of the
micrometeoroids are no longer recognisable as Perseids judging by the
low telescopic rates. A plot from the ecliptic or stream pole makes
this evident. There is one such plot in Porubcan (1977, BAC 28 p257,
plot p.265). So to answer's Lew's question in part, the orbital
elements do vary. I recollect seeing a clearer plot than this in
recent years, but I can't recall the reference. It might have been in
a David Hughes paper. Does anyone know the reference please?
The original radiant size came from double-station photographic work
analysed by Porubcan (1970, BAC 21, p153). What I'd like to know is
whether the new Perseid peak has different radiant characteristics
from the traditional one. Also what are the radiant sizes for typical
+3 visual meteors as opposed to photographic ones, as the latter
should arise from more-massive and hence less-perturbed meteoroids?
Both of the papers mentioned above are available from the ADS abstract
service http://adsabs.harvarddot edu/.
Malcolm
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