Transcript Easy way to estimate meteor brightness on TV frames

Easy way to estimate meteor
brightness on TV frames
V.A.Leonov and A.V.Bagrov
Institute of Astronomy
of Russian Academy of Science
Meteor brightness is very valuable
characteristic
It is necessary to:
-calculate ZHR
-Obtaine population index
-Estimate meteor particle mass
-Analyze physical properties of meteor particles and so on
Observers often reports of very
weak meteor observed
Thomas Weiland this morning reported that nearly
48% of visually observed meteors had brightness +4
and +5 magnitudes. He underlined that no short treks
was registered
A common method to estimate meteor brightness is to
compare meteor view with a star that looks as bright as
meteor and declare that both of them has equal
brightness's. But this method is correct for point-like
images only. Mainly meteors are not.
What is star brightness?
The astrophysical catalogues presents brighness’s of stars
in specific spectral bands that are good for stellar
astrophysics and slightly concern meteor brightness’s
estimated in whole visual (photographic, opto-electronic)
bands. So cold “visual” V band is close to visual human eye
sensitivity, so visual observers may use mv star brightness
to measure (at least) relative meteor magnitude.
To have a correct catalogue of reference stars brightness’s
we present a list of 93 non-variable bright stars with their
brightness’s in energetic units (Poster N 16 at our
Conference) for spectral band of TV-systems with WATEC
cameras
Meteor is not point-like event
The photons from meteors are distributed over its trek, so
response of its light is lower then if it were point-like.
Visible brightness in any point of trek can be estimated by
referent star brightness, but light flux from meteor,
evidently, is much more then flux from a star. To get its
proper value one have to add “velocity index” to the
brightness of reference star.
For visual observations it is very hard to determine
correctly this velocity index, because meteor angular
velocity only very skillful observers can estimate properly.
But it is easy to get it from TV-registrations.
Based idea
One can roughly estimate length of meteor trek l in
units of resolution element’s dimension d. Then
effective exposition of every point of meteor trek will
be τd/2l sec. (τ – exposure time)
The proper brightness of meteor will be equal stellar
magnitude of similar brightness referent star added by
-2.5lg(d/l).
The correction factor -2.5lg(d/l) depends only of
relative length of meteor trek, so it may be estimated
as a function of l/d ratio
Tabulated values of velocity index
l/d =
2
3
4
5
6
Δm =
-0.75
-1.2
-1.5
-1.75
-2.0
l/d =
7
8
9
10
12
16
Δm =
-2.1
-2.26
-2.4
-2.5
-2.7
-3.0
Typical pictures
Very bright meteors can be seen short.
Weak meteors cannot be detected being short
Typical pictures
Even such short treks mean that meteor is 1.5 magn
brighter then similar star
Typical pictures
The longer meteor trek is the brighter is the meteor.
Telescopic meteors
All mentioned above is correct for equal exposure time for
referent star and meteor. During telescopic meteor
observations this cannot be proved. When visual observer
looks to ocular, his eye collect light from star nearly 0.07
sec though meteor may be tens times shorter. So real
meteor brightness even visually looking like weakest stars
in the field of view is several magnitudes brigher.
Thank You!