Electronic Telegram No. 2819
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


DRACONID METEORS 2011
     P. Jenniskens, SETI Institute, reports that the earth is predicted to
encounter the 1900 dust ejecta of comet 21P/Giacobini-Zinner on 2011
Oct. 8d20h01m UT.  This is expected to result in a brief-duration (about 3 hr)
outburst of Draconid meteors with a peak Zenith Hourly Rate (ZHR) of about 600
meteors per hour.  The best viewing will be from sites in Europe and North
Africa, away from moonlight at high altitude; the moon will be 91-percent
illuminated.
     This is the same dust ejecta that may have been responsible for the 1933
and 1946 Draconid storms, which caused higher Draconid rates than expected
from the dust trail crossings in other years (Watanabe and Sato 2008, EMP
102, 111-116).  According to Jenniskens, the 1900 dust ejecta may have been the
product of comet fragmentation from the return of 1900, when the comet was
discovered.  The meteoroids observed in 1946 were unusually fragile, with
shallow penetration depths and irregular light curves, possibly because the
grains were ejected in an ice-laden form, releasing the water ice gently after
ejection.  In that case, no second peak of enhanced rates are expected around
Oct. 8d17h UT, when the earth would encounter dust ejected in 1873-1894.
     The forecast by J. Vaubaillon et al. (2011, JIMO 39, 59-63) puts the peak
rate at ZHR = 600 meteors/hr at 20h01m UT, with meteors radiating from R.A. =
263.2 deg, Decl. = +55.8 deg, with V_g = 20.9 km/s; Vaubaillon also forecasts
a ZHR of about 60 meteors/hr, centered on Oct. 8d17h UT, from crossing the
1873-1894 dust ejecta of the comet, assuming that it was active at that time.
M. Sato (National Astronomical Observatory of Japan) expects a peak rate of
ZHR = 500 meteors/hr around 20h36m UT.  D. Moser and W. J. Cooke predict a
peak rate of ZHR = 750 meteors/hr, centered on 19h52m UT (see website URL
http://tinyurl.com/3z5whgg).  M. Maslov (2011, JIMO 39, 64-67), on the other
hand, does not expect high rates, with the ZHR peaking at only 40-50 meteors
per hour around 20h13m UT, because of a relatively large miss distance (see
website URL http://feraj.narod.ru/Radiants/Predictions/21p-ids2011eng.html).
Models by Vaubaillon, however, show the dust to be spread into the path of
the earth.  E. Lyytinen (Helsinki, Finland) calculated a peak of ZHR = 150
meteors per hour at 20h12m UT, with a full-width-at-half-maximum duration of
70 min.


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

                         (C) Copyright 2011 CBAT
2011 September 12                (CBET 2819)              Daniel W. E. Green