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View Full Version : Can Hot Ionized Medium be called nebula? X-rays source in it, and the cooling mech...



tu144
2011-May-28, 11:42 AM
I've read that Hot Ionized Medium can be also called Coronal Cloud.
Is it also a type of nebula, or the term nebula has it's limits somewhere?
What is the primary way that such cloud uses to cool itself?
I've been able to find some cooling mechanisms for ISM, but not for HIM in particular.
I assume that the x-rays come form highly ionized heavy elements in the cloud.
Now, at this point some questions arise in my head.
Do the cloud get rid of more energy using high energy photones, or from a large amount of some less energetic photones coming from hydrogen lines or other light element?
Can these x-ray photones get out easily from this cloud?
OR cooling comes mainly from some lower energetic transitions (fine structure cooling, just like with normal HII regions) that are in infrared and radio and can leave the cloud very easily?

ngc3314
2011-May-28, 01:45 PM
Hint: while there are transitions from metal ions (especially inner-shell transitions in highly ionized species), brehmsstrahlung (free-free radiation) is very important over a wide rage of temperatures from a few x 106 to a few x 107 K. Above energies of 2 keV or so, almost al the ISM clouds we might deal with are optically thin to X-rays (unless, say, you are looking into a heavily shrouded AGN or right at our own galactic center, where X-rays only escape freely at higher energies.).

(I can't resist pointing out that, if your professors where you are enrolled don't have enough time for your questions on your timetable, the time of professors at other distant institutions, who have their own actual class timetables to keep, might be considered a resource to use carefully!)

tu144
2011-May-28, 09:25 PM
Hint: while there are transitions from metal ions (especially inner-shell transitions in highly ionized species), brehmsstrahlung (free-free radiation) is very important over a wide rage of temperatures from a few x 106 to a few x 107 K. Above energies of 2 keV or so, almost al the ISM clouds we might deal with are optically thin to X-rays (unless, say, you are looking into a heavily shrouded AGN or right at our own galactic center, where X-rays only escape freely at higher energies.).

Got it. Thanks!





(I can't resist pointing out that, if your professors where you are enrolled don't have enough time for your questions on your timetable, the time of professors at other distant institutions, who have their own actual class timetables to keep, might be considered a resource to use carefully!)
Yeah, I know. I'll try to be more selective if it comes to asking questions here.