Talk:H II region

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Contents 1 Forbidden lines 2 Density 3 "giant H II region" 4 H II regions as plasma 5   6 stellar nurseries?

[edit] Forbidden lines

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)

[edit]  

I don't see that the   scattered throughout the article are needed. I do find that they make the article hard to maintain and would like to see them removed unless there is a compelling reason to include them. I've seen no other articles where they are used like they are here and believe they are not needed here as currently used. My fix for this was reverted by an anonymous user twice claiming that they are needed. WilliamKF 22:13, 5 January 2007 (UTC)

It means that, on the page and in print, you won't get H at the end of one line and II at the beginning of the next. It's just good sense to keep them together with nbsps, as having the thing split across lines looks ugly and confusing. I'm curious as to why your edit summaries did not correspond with what you were actually doing? Both times you removed all the nbsps, your edit summary claimed to be correcting a spelling (which didn't need correcting in any case). 81.178.208.69 23:35, 5 January 2007 (UTC)

The edit summaries are automatically generated by AWB. It wanted to correct spelling of Sargent which I manually undid, however, the edit summary did not know that I had undone its work. WilliamKF 00:04, 6 January 2007 (UTC)

Is it not possible to change the edit summary to reflect what's actually happening? I wasn't sure, seeing an identical edit with incorrect summary twice in quick succession, if your software was making a mistake, if you were aware of what it was actually doing, or what. Do you agree with my reasons why the nbsps should stay? 81.178.208.69 14:41, 6 January 2007 (UTC)

You can't directly edit the edit summary from AWB, but instead can pick from a set of choices, I picked 'clean up' which gets appended with the spelling changes which I manually backed out. Agree with keeping the nbsp now that I understand their use. I hit it twice (and thought Deja-vu, because my search criteria hit upon it twice for two different tasks.) I notified the AWB maintainers and they have already removed the correction of Sargent since it is a name for the next release of AWB. WilliamKF 17:37, 6 January 2007 (UTC)

[edit] stellar nurseries?

I would edit this article in several places to change where the article refers to HII regions being the "birthplaces of stars". This is not really correct.

Molecular clouds are the birthplaces of stars. HII regions are commonly found in parts of molecular clouds, where young massive stars have already formed and are ionizing and blowing away the surrounding cold molecular hydrogen. The gas in the HII region itself, being ionized, will NEVER collapse into a star. If anything, to use the given metaphor, an HII region is part a stellar nursery being systematically destroyed by the first baby to arrive, whatever's within reach of its basinet. A few other babies can hide in their dark corners for a while and continue to grow, but the UV from the massive ones are photo-evaporating the clouds the little ones are trying to collapse in, stopping them in their tracks. That is, the massive stars can interrupt the more slowly collapsing low-mass stars from growing, and actually prevent some of them from ever gaining enough mass to become stars. I saw a paper presented at AAS meeting this year predicting just that occurring in the Eagle Nebula (the famous "pillars of creation"). Myrrhlin 21:40, 16 April 2007 (UTC)