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(meteorobs) [IMO-News] Re: Where are the faint Leonids?
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Date: Mon, 29 Nov 1999 13:30:19 +0000
To: imo-news@egroups.com
From: Detlef Koschny <dkoschny@estec.esadot nl>
In-Reply-To: <41256838.00437EC8.00@estecmail1.estec.esadot nl>
Subject: [IMO-News] Re: Where are the faint Leonids?
Sirko,
a first check of our tapes (about 240 hours in total, with 8 different
cameras) confirms what you say: the number of meteors is highest for our
"LCC" cameras, which have a field of view of about 30 deg (dia) and lm
around 5.5. Our "ICC" cameras have only 12 x 15 deg2, lm is 9 - but they
see less meteors. I also think that the number of faint meteors (fainter
than 5 or 6) did not increase as much as the visual meteors.
Detlef.
At 12:18 PM 11/29/99 +0000, you wrote:
>
>
>It is well-known that the Leonid simulations carried out by Asher,
>McNaught, and others predicted an outburst of faint meteors on Nov 18, 1999,
>2:08 UT. Indeed, a meteor storm with maximum eZHRs in the order of 5,000
>was witnessed by numerous observers in Europe at the given time. Fireballs
>were almost absent, and the majority of Leonids were of third or fourth
>magnitude, thus, quite faint.
>
>However, the preliminary analysis of video observations carried out by
>member of the German AKM meteor group draws a slightly different picture.
>At our observing site near Malaga/Spain (4 deg W, 37 deg N) two image
>intensified video cameras were operated during the storm:
>
>AVIS : 1.5/100 mm lens, fov = 15 deg, lm ~9 mag
>CARMEN : 1.8/28 mm lens, fov = 35 deg, lm ~6 mag
>
>The center of fov of both cameras was fixed at 54 deg azimuth and 43 deg
>altitude.
>
>The field of view of CARMEN was about 5.5 times as large as the fov of AVIS.
>On the other hand, it's limiting magnitude was about 3 mag brighter. Given a
>conservative low estimate of 2.0 for the population index of the Leonids at
>the maximum one would expect that AVIS recorded (2^3)/5.5 = ~1.5 times
>as much Leonids as CARMEN. However, on the contrary, the wide angle camera
>recorded more than twice as much Leonids as the one with the better
>limiting magnitude:
>
>AVIS : 165 Leonids (01:00-03:00 UT)
>CARMEN: 393 Leonids (01:00-03:00 UT)
>
>The difference becomes even more prominent if we consider only meteors whose
>begin (124 vs. 373 Leonids) or end point (89 vs. 325 Leonids) was inside the
>field of view of the camera.
>
>On the other hand, AVIS recorded about five times as much non-Leonid meteors
>(90 vs. 19), which is in good agreement with an average r-value of 3.0 for
>those.
>
>How can this contradiction be explained? At www.imodot net/leo99 a graph
>with preliminary brightness distributions of the video meteors is shown.
>In contrast to visual observers, the detection probability of video systems
>is almost one until about two mag above the limiting magnitude. Hence,
>the cumulative meteor counts are almost complete for meteors <= 6 mag (AVIS)
>and <= 4 mag (CARMEN), respectively.
>The derived population index is near 3.0 for bright Leonids (0..2 mag), and
>decreases to values below 2.0 for Leonids in the order of 3 mag, and to a
>value below 1.5 for Leonids fainter than 5 mag.
>
>>From that it seems that smaller Leonid meteoroids are not that abundant
>anymore, which is why starting at about 3 mag the number of Leonids
>increases much slower towards fainter magnitude classes.
>
>The second graph shows the detailed Leonid counts per minute, averaged in
>sliding 3 minute intervalls. The activity profiles obtained from data
>of both cameras show a number of distinct peaks of similar strength at 1:52,
>1:58, 2:06, 2:12, and 2:18 UT. The 1:52 and 2:12 peaks seem to be most
>prominent in both profiles. The times are not corrected for the topocentric
>time of the stream encounter.
>
>We would like to know about the results of other video observers to check,
>whether our results are confirmed by other cameras. Please, send your video
>observing data to video@imodot net. You can also contact me if you need help
>for the inspection of your video tapes.
>
>Sirko Molau
>
>PS: At the given web address, you find also a nice sum image of 99 bright
>Leonids recorded between 1:44 and 2:15 by CARMEN.
>
>----------------------------------------
>Sirko Molau -- Video Commission Director
>International Meteor Organization
>e-mail: video@imodot net
>WWW : http://www.imodot net/video
>----------------------------------------
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Detlef Koschny email: dkoschny@estec.esadot nl
European Space Agency
ESTEC Sci/SO
Keplerlaan 1 phone: +31-71-565-4828
NL-2201 AZ Noordwijk ZH fax: +31-71-565-4697
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