Quote:
Originally Posted by sjastro
OIII emissions are examples of "forbidden transitions".
In fact OIII emissions have never been observed in the laboratory. Excited O atoms in the laboratory lose energy through collisions making forbidden transitions extremely unlikely.
Not so in outer space. The density of your emission nebula, planetary nebula or SNR remnant is so low compared to a "laboratory sample" that the O atoms do not lose energy through collisions. Excited O atoms can exist in a an extended excited transition state, and the probability of a transition to a lower energy or ground state via a forbidden transition is greatly increased.
Steven
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An interesting and strongly-physical perspective, Steven.
Sounds like it comes from someone who has had intensive physics training, unlike me (my approach, all my life, has been to learn only the physics & maths that is absolutely necessary for me to understand the astronomy I happen to be studying, but no more than that)
Q. All the astrophysics books talk about 'collisional excitation' (which
sounds like a very exciting type of excitation!) of the OIII ion, but they never mention if there are any transitions of this atom that can be set off by energy that is provided to the atom by photons (that is, by electromagnetic radiation).
Can OIII be excited by a photon?
I am buying a copy of the aforementioned book "Atomic Astrophysics and Spectroscopy", because I find that most astrophysics textbooks only give a sketch of physical processes in ionized gas regions.
One book that I do use is "Physics of the Interstellar and Intergalactic Medium", (2011), by Bruce T. Draine, (Princeton University Press)(ISBN: 9780691122144).
I find this solidly graduate-level text to be heavy going, for the most part, and I have to keep referring back to physics textbooks when I use it, because I only have a unit or three of tertiary-level physics.
[ A more famous book is Osterbrock & Ferland (2005) "Astrophysics of Gaseous Nebulae and Active Galactic Nuclei."]
I find that while I do own lots of easier books about the ISM, I am still forced to tiptoe through graduate level texts, as the interstellar medium is so remarkable in its complexity!
There seem to be a lot of high-level ISM books coming out, of late (by: A.G.G.M Tielens, Sun Kwok, the Draine book that I mentioned, etc). I wonder if anyone is reading them?