Electronic Telegram No. 255
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


DRACONID METEORS 2005
     M. Campbell-Brown, P. Brown, and P. Wiegert, University of
Western Ontario (UWO), report that radar observations at 28 and 38
MHz by the UWO's Canadian Meteor Orbit Radar indicate an outburst
of Draconid meteors centered at solar longitude L = 195.44 +/- 0.02
degrees (equinox 2000.0), corresponding to Oct. 8.71 UT, with a
duration of approximately 2 hr.  Peak hourly fluxes to a limiting
equivalent radar magnitude of +6.5 (corresponding to a mass of
about 10**-6 kg) were 0.15 meteoroid km**-2 hr**-1.  (Radar
monitoring over the previous five years showed almost no detectable
"radiant spots" near the Draconid radiant at the time of maximum,
attesting to very low rates.)  The duration of the 2005 outburst
is uncertain, as the UWO radar sensitivity begins to drop rapidly
near the tail end of the outburst time.  Assuming a population index
of 3.0 (as measured for the 1998 and 1985 Draconid outbursts), this
corresponds to an equivalent ZHR near 150.  Visual observations from
the International Meteor Organisation (via R. Arlt) suggest a minor
enhancement of visual Draconid activity between L = 195.38 and
195.5 deg (corresponding to Oct. 8.65-8.78) with a peak ZHR near 40
(no bright meteors were noted).  J. Vaubaillon (UWO) notes that
ejecta from comet 21P/Giacobini-Zinner at its 1946 passage intersect
the earth near this time (with a peak slightly earlier) for meteoroids
of radius 50-100 microns (i.e., sub-visual sizes) for a time interval
of 2.5 hr; in his simulation, larger particles are much less favored for
earth intersection, and this can explain the larger ZHR at small radar
masses as compared to the visual data.  (Previous simulations by
Vaubaillon and others were confined to larger particles -- appropriate
to the gram-sized particles associated with visual observations -- and
had predicted that no particular enhancement or special activity was
likely in 2005.)  Note that the time of the peak in 2005 corresponds
(within errors of the outburst peak location) to the earth's nodal
passage through the orbital plane of 21P.  The following mean orbital
elements (with standard errors), based on 63 orbits measured during the
2005 outburst, are consistent with the Draconid-stream orbital elements
determined from past photographic observations:  a = 3.456 +/- 0.177 AU,
e = 0.679 +/- 0.012, q = 0.988 +/- 0.0005 AU, Peri. = 166.634 +/- 0.311
deg, Node = 195.418 +/- 0.014 deg, i = 29.830 +/- 0.266 deg (equinox
2000.0), mean velocity in the atmosphere = 22.8 +/- 0.2 km/s.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2005 CBAT
2005 October 14                  (CBET 255)               Daniel W. E. Green