Talk:H II region

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H II region is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. If you can update or improve it, please do.

H II region appeared on Wikipedia's Main Page as Today's featured article on February 2, 2005.

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Would "forbidden lines" be the same as "absorption lines"? I here that term a lot when speaking of stellar spectra, but I've never heard them called "forbidden". -- John Owens 15:08 Apr 7, 2003 (UTC)

"forbidden lines" can be of the absorption or emission kind (rules are the same), these lines corresponds to energy transitions which should never occurs (forbidden by the transition rules, generaly because of symmetry reasons), but which, nevertheless, occurs (usually at a very lower intensity) when taking into account all the interactions (causing a small symetry breaking/split of an energy level/...). For example, for infrared lines, collisions between molecules induces small distorsions, which reduce the symmetry, which make possible some transitions otherwise forbidden in the full symmetric case. Need an article of course. -- looxix 17:47 Apr 7, 2003 (UTC)

OK, now that we've got a forbidden lines article in place, I see what you mean. :) All I knew from the context here was that they weren't emission lines, so I figured they must then be absorption lines. Neat to know about those too, now. -- John Owens 19:04 Apr 7, 2003 (UTC)

[edit] Density

Related to density, article says that nebulas have [10 - 10,000,000] particles per cm^3. Could someone explain me to what presure that compares? How many particles per cm3 we have in lab-made vacuum, for instance? saigon_from_europe

[edit] "giant H II region"

Am I seeing things or is the "giant H II region" image on the article's top right one of those goatse photoshops?

[edit] H II regions as plasma

I restored the text regarding H II regions as plasmas. The following points seem reasonable:

• H II regions are completely ionized, so by definition, are plasma.
• All plasmas, by definition, have the characteristic of plasma.
• Any magnetic field entering a plasma is carried by the plasma, just as the Sun's "open" magnetic field extend to infitinity.
• I've added a reference to the interstellar medium, and hence H II region having a magenetic field.
• All magnetic fields in motion produce a current, just as the movement of the interplanetary medium in the Sun's magnetic field produces the heliospheric current sheet.
• I've added two references to electric currents in the interstellar medium

--Iantresman 23:30, 8 October 2005 (UTC)

The term "H II" is not well defined. Even after looking at the references there is no mention of doubly ionized Hydrogen or even that it is the COOLING (recombination) of the gas that causes the visible emission.

HII is singly ionized hydrogen. The notation is [chemical symbol][roman numeral] where roman numeral I indicates that the element is neutral. Keflavich 22:40, 30 November 2005 (UTC)

On another note... how do you get to this page? I can't access it by going to "hii region" or "h ii region" or any other variation. Links work fine though. --Keflavich 23:16, 30 November 2005 (UTC)

A hydrogen atom only has one electron, so "doubly ionzed" hydrogen (H⁺²) is impossible. As Keflavich says, HI means neutral atomic hydrogen (H - i.e. one proton and one electron), and HI means singly ionized atomic hydrogen (H⁺ - i.e. a bare proton}. Molecular hydrogen would be H₂. The article can be lined as H II region (note the capitalisation). -- ALoan (Talk) 10:30, 1 December 2005 (UTC)

Thanks. I was unaware that the search/go function was case sensitive --Keflavich 20:54, 1 December 2005 (UTC)