(meteorobs) Draconids: population index & ZHR

[Geert Barentsen]

All,

Based on 2164 Draconid magnitudes reported to the IMO by visual observers, I
computed a population index of:

r = 2.8 +/- 0.05   (for October 8, 16h00-24h00 UT).

This suggests that the Draconid outburst consisted mainly of faint meteors,
as expected. The visual graph at www.imo.net has now been updated to take
this value into account. This has the effect of raising the peak ZHR from
~350 (under the previous assumption of r=2.6) to ZHR ~400 (assuming r=2.8)
near 20h00m +/- 10m UT. However, it must be made clear that absolute values
for the ZHR are known to be uncertain during periods of full moon, perhaps
by up to +/- 50%.

Nevertheless, it appears that the observations match the predictions in a
very impressive way. Congratulations to all involved!

The magnitudes required to compute the population index are available in
machine-readable format at the bottom of:
http://www.imo.net/live/draconids2011 .
The computation method used is described in (Arlt et al. 2003):
http://adsabs.harvard.edu/abs/2003JIMO...31...77A

Best wishes,
Geert
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