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(meteorobs) Leonid activity update

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       I M O   S h o w e r   C i r c u l a r

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               LEONID Activity 1999
               ====================
                      UPDATE
               ====================

New ZHR calculations have been made. On the one hand, newly 
received observations have been included, and, on the other hand, 
data based on estimated counts have been replaced by data based 
on actual counts.

Visual observations of the 1999 Leonids revealed a distinctive 
peak with a ZHR of about 5000 on November 18, 2h04m +/-5m UT 
(solar longitude 235.286 +/- 0.004, eq. 2000.0). Ten minutes
earlier, at 1h53m +/- 5m UT (solar longitude 235.278 +/- 0.004,
eq. 2000.0), the ZHR profile shows a secondary peak with of ZHR of
about 3500. This secondary peak does not only occur in the combined
ZHR profile below, but also in the ZHR profile of several 
individual observers, and is therefore probably real.
Apart from this secondary peak, the ZHR profile looks remarkably
smooth, even at the level of 5-minute intervals. 

ZHR levels were above 1000 from roughly 1h20m UT to 2h45m UT
corresponding to 235.26 to 235.31 degrees in solar longitude. 

All observers who were able to view the peak under good sky 
conditions reported an abundance of faint meteors and a relative 
absence of fireballs. Some observers noticed a drop in the 
population index (i.e., a larger fraction of brighter meteors) 
after the peak.

Reports from Mohammad Odeh (Jordanian Astronomical Society), 
Casper ter Kuile (Dutch Meteor Society, observing near 
Valencia, Spain), and Ilan Manulis (Israel) are very consistent 
with the picture sketched  above.

In addition, radio data from K. Maegawa (Toyokawa Meteor Observatory, 
Aichi, Japan) reported by Kazuhiro Suzuki and the backscatter
radar data from Ondrejov Observatory (Czech Republic) reported by
Petr Pridal and Rosta Stork yield a peak time between 2h00m UT
and 2h10m UT.

It seems that the peak time of 2h08m UT predicted by Asher/McNaught
is confirmed within a margin of at most a few minutes, although the
observed activity is significantly higher. It is reasonable to
conclude that the peak activity has been caused by the 3-revolutions
old dust trail of 55P/Tempel-Tuttle.

The following observers (with their observing sites, not their
nationality or country of residence) have contributed data immediately
after the event, from which the ZHR profile given below 
has been derived:

Rainer Arlt (Spain), Felix Betonvil (Canary Islands), C.L. Chan 
(China), Mark Davis (USA), Asdai Diaz (Cuba), Yuwei  Fan (China), 
Fei Gao (China), Lew Gramer (USA), Rafael Haag (Brazil), 
Dave Hostetter (USA), Andre Knoefel (Spain), Detlef Koschny (Spain), 
Wen Kou (China), Alastair McBeath (UK), Alfredo Pereira (Portugal), 
Josep Ma. Trigo-Rodriguez (Spain), Helena Valero-Rodriguez (Spain), 
Renke Song (China), Wanfang Song (China), Jan Verbert (France), 
Catarina Vitorino (Portugal), Jean-Marc Wislez (France), Mariusz 
Wisniewski (Poland), Dan Xia (China), Dongyan Zha (China), 
Jinghui Zhang (China), Yan Zhang (China), Jin Zhu (China).

(For groups of observers, only the name of the contributing
observers have been mentioned.)

Date   Period (UT)  Time (UT)  Sol. Long.  ZHR	 +/-
-----------------------------------------------------------
Nov 17 0600-1000    0800       234.527       16     2
Nov 17 1600-2010    1805       234.951       30     5
Nov 17 1900-2200    2030       235.052       53    14
Nov 17 2300-2400    2330       235.178       82     6
Nov 18 0000-0050    0026       235.217      210    60
Nov 18 0030-0100    0048       235.233      370    80
Nov 18 0050-0130    0110       235.248      560    90
Nov 18 0115-0145    0132       235.263     1160   180
Nov 18 0139-0155    0148       235.275     2360   600
Nov 18 0145-0200    0153       235.278     3430   750
Nov 18 0154-0205    0158       235.282     2820   550
Nov 18 0159-0209    0204       235.286     5400   880
Nov 18 0200-0215    0209       235.289     3540   580
Nov 18 0212-0233    0222       235.298     2110   580
Nov 18 0223-0247    0238       235.310     1140   280
Nov 18 0244-0320    0257       235.323      690   150
Nov 18 0315-0400    0340       235.353      240    60
Nov 18 0347-0505    0423       235.383      153    59
Nov 18 0512-0712    0557       235.449       61    12
Nov 18 0700-1100    0905       235.581       44     5

ZHRs are computed with a population index of 2.0, zenithal
exponent of 1.0.

---
Marc Gyssens, 1999 November 18, 7h UT.
wgn@imodot net
---

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