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Re: (meteorobs) RE: trails, trains, etc

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From: Gural, Peter S. <PETER.S.GURAL@saic.com>
Subject: (meteorobs) RE: trails, trains, etc


> Ed Majden posted an excellent page on meteor definitions and descriptions
> but I was puzzled by the last statement near the end of section 2
paragraph
> 1 on meteor trains reproduced here:
> ------------------------------------------------------
>  2. SHORT-DURATION METEOR TRAINS (OR TRAILS)
>
>  Luminous trains left behind the meteor for up to about 3 seconds.
>  They are often observed visually and by video techniques in fast
>  meteors like Perseids. They are present also in faint meteors, of
>  magnitude +4 or so. In fact the ratio of the train/meteor brightness is
>  larger in faint meteors than in bright meteors. The train is not
>  connected with the meteor. In fact, it forms at a given position
>  with some delay after the meteor passage. The the train is also
>  considerably shifted to higher altitudes than the meteor which produced
>  it.
> ---------
> I would have thought that trains are produced along the meteor's path so
> what does it mean they are shifted to higher altitudes? Do these trains
> occur back along the meteor track (higher altitudes) that are beyond the
> visible portion of the initial meteor's illuminated track?
>

Pete:
    Jiri, I believe is referring to the forbidden line of 0 I (3F) at 557.7
nm, (the auroral green line).  In general this line appears in meteor
spectra with velocities over 40 km/s and beginning about 10 km higher than
the main spectrum.  In Jiri's MAP paper on the 1998 Leonids in the Nov 1999
issue states, this line reaches its maximum intensity with some delay (~0.l
s) after the meteor passage at a given location and then decays gradually
for 1-2 seconds.  This line was first identified by Halliday in 1958.
Because of its persistence you can see this line smeared across chopping
shutter breaks.  Halliday later developed a jumping film camera which
enabled a more detailed study.  With my spectra video set-up I hope to do a
study of the comings and goings of this line in Perseid spectra.  Duration
of appearance as compared to other features etc. With this in mind, do you
know the average persistence duration of the image screen of a 2nd
generation MCP image intensifier?  This should be known or it will distort
the length of the train duration.

Ed Majden

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