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 m v 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 = Δm = l/d = Δm =

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!