(meteorobs) Green Fireballs

[Ed Majden]

Hi Chris:

Your quote on meteorobs:



"The green seen in fireballs comes from atmospheric oxygen.  
Composition can
be seen spectroscopically in emission lines, but the visual color is  
pretty
much useless for assessing composition. All the different emission lines
push the apparent color towards visual white, and no single emission  
line
can be strong enough to strongly influence that."

Chris

	I don't think you can make a blank statement that the green in  
fireballs comes from atmospheric oxygen.  Oxygen is found in  
fireballs with velocities greater than 40 km/sec.  This is especially  
true of the persistent radiation of the so called forbidden line of  
[ 0 ] at 557.7 nm first identified by Ian Halliday in 1958.  This  
line is not present in slower fireballs like the types originating  
from asteroids and likely to drop a meteorite.  I have discussed this  
with Jiri Borovicka and he says that slow fireballs do not have  
bright emissions in the near IR, (in contrast to fast fireballs like  
the Perseids, which have O I, NI, Ca II emissions.  I would think  
that Mg I and Mg II would be contributing to the green rather than  
Oxygen as you suggest. I agree that you cannot determine the fireball  
type from its apparent colour.  A lot still has to be learned from  
meteor spectra.  We need to record the spectrum of a fireball that  
has dropped a meteorite which has been recovered.  It would be  
interesting to compare the elements found in the actual meteorite  
with the spectrum of the fireball in the atmosphere.  This would  
clear up may questions that have not been answered yet.

Ed Majden