[IAUC] CBET 1108: 20071025 : ORIONID METEORS 2007 [this text replaces that on CBET 1107]

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                                                  Electronic Telegram No. 1108
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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ORIONID METEORS 2007  [this text replaces that on CBET 1107]
     Following last year's elevated rates (cf. CBET 698), P. Jenniskens,
SETI Institute, reports that the annual Orionid shower has again been
stronger and brighter than expected in 2007.  In the period 2007 Oct.
4-23, Orionid shower rates reported by the International Meteor
Organization were 80 percent higher than normal, peaking at ZHR = 45 per
hour on Oct. 22d11h UT.  Furthermore, a 1-day-wide outburst occurred with
a peak rate of ZHR = 25/hr, centered on solar longitude 208.15 +/- 0.05
deg (equinox 2000.0; Oct. 22d01h), similar to other such outbursts observed
in 1993 and 2006.  The total rate peaked at 65 +/- 3 per hour, stronger than
in 2006.  From single-station video observations, I. Yrjola, Kuusankoski,
Finland, measured radiant positions at R.A. = 94.7 deg, Decl. = +16.0 deg
on Oct. 21.03 (55 meteors); R.A. = 95.7 deg, Decl. = +16.0 deg on Oct. 22.04
(96 meteors); and R.A. = 96.9 deg, Decl. = +14.0 deg on Oct. 23.03 (57
meteors).  From three-station video observations, E. Lyytinen  (Helsinki,
Finland) reports mean radiants of R.A. = 94.9 deg, Decl. = +15.7 deg on Oct.
21.0; R.A. = 95.8 deg, Decl. = +15.6 deg on Oct. 22.0; and R.A. = 96.4 deg,
Decl. = +15.9 deg on Oct. 23.0.
     J. M. Trigo-Rodriguez, Institute of Space Sciences (Consejo Superior
Investigaciones Cientificas) and Institut d'Estudis Espacials de Catalunya,
reports that high-resolution CCD all-sky and wide-field CCD imagery recorded
by the Spanish Meteor and Fireball Network (SPMN) showed an outburst of the
Orionid shower during Oct. 19d02h00m-19d03h30m UT.  Observations were made
from the Montsec Astronomical Observatory and Montseny stations, and
activity was mainly composed of bright meteors and fireballs with ZHR =
40 +/- 10, peaking at 3h00m +/- 30m UT (solar longitude 205.47 deg).
Additional confirmation of the outburst was obtained by three SPMN video
stations operated by J. M. Madiedo (Universidad de Huelva) located in
Seville and Huelva.  Video and small-field CCD imagery shows the presence of
fainter meteors than those imaged from all-sky CCD cameras.  Video data and
parallel visual observations suggest that the outburst was also composed of
meteors as faint as mag 6.  On Oct. 19, all meteors (except for a weak
background) were coming from a very compact radiant located at R.A. = 90.2
+/- 0.1 deg, Decl. = 14.8 +/- 0.1 deg (equinox 2000.0, from 12 CCD meteors).
The magnitude distribution index (chi) was 1.5 +/- 0.4.  On Oct. 19-20,
Orionid activity decreased to ZHR = 25 +/- 5, still exhibiting bright
meteors in all-sky CCD and video cameras.  Video and visual data indicate
that the activity was dominated by fainter meteors than on the previous
night (chi = 1.8 +/- 0.4).  On Oct. 20-21, Orionid activity increased to ZHR
= 60 +/- 10, produced by bright meteors and abundant fireballs from a
compact radiant located at R.A. = 95.3 +/- 0.4 deg, Decl. = 15.7 +/- 0.2 deg
(from 18 video meteors).  Consequently, the magnitude distribution decreased
to chi = 1.5 +/- 0.4.  On that night, several very bright (mag -8 to -12)
fireballs were recorded over Spain before sunrise, and their emission
spectra were obtained with high-sensitivity video devices.  The brightest
recorded event was a daylight Orionid bolide recorded by J. M. Madiedo
(Universidad de Huelva) on Oct. 21, at 6h07m54s UT over the province of
Huelva.  During the following nights, increased activity of bright Orionid
meteors by SPMN cameras has been still ongoing.
      According to Jenniskens, annual Orionid shower rates should continue
to be elevated in the next two weeks, when the shower activity declines.


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

                         (C) Copyright 2007 CBAT
2007 October 25                  (CBET 1108)              Daniel W. E. Green