Talk:CNO cycle

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Bug in energy yield?
The reaction: 15 8O 	  	  	→  	15 7N 	+  	e+  	+  	ν e 	+  	2.75 MeV 	(half-life of 122.24 seconds)

appears twice with yields of 2.75 and 1.73 mev yield, but are otherwise identical. Which, or (my physics is weak) both?

early discussion before TOC
"The CNO cycle may also be the dominant source of nitrogen and oxygen production"

Er, how? It doesn't create a net increase in the number of N or O nuclei. -- Bth


 * Maybe what is meant is that once there is carbon in the star, there will also be nitrogene and oxgene in a comparable amount. If there is no other direct synthesis for oxygene and nitrogene, then most of these two elements can come from aborted CNO cyles. andy 22:32, 29 Feb 2004 (UTC)

There is an equilibrium concentration N and O available in stars. When stars cool down, this can form N2 and O2. In heavier stars, when hydrogen/helium is depleted CNO starts reacting with other CNO molecules to form silicium (and slightly heavier components).


 * If the protons run out, you've still got a lot of CNO...Sikkema 14:23, 2 October 2007 (UTC)

energy notation
Is it a convention to write anenergy yield, so the liberation of energy, in the positive form ? This is contrary to chemical convention. Sikkema 14:23, 2 October 2007 (UTC)


 * As far as I know, at least the same notation is used as in chemistry

HELP!!! :S
Hi i have a little question that you may just be able to help me with well here it goes... What type of radioactive particle was emitted by 13/7N and 15/7N? your help is much appriciated thank you

- 13N-> beta+ + 13C (no gamma) 15N stable, abundance 0.366%

Reference to the Bethe paper
The link below point to the paper of Hans Bethe in which he introduces the CNO cycle.

http://prola.aps.org/abstract/PR/v55/i5/p434_1

Bethe-Weizsäcker process
The german wiki calls it Bethe-Weizsäcker process is this also a name for it?--Stone 11:27, 30 June 2006 (UTC)


 * The article has since been changed to reflect this, but my feeling is the CN cycle (or CNO-I) is that cycle, and the rest are not. Maybe Bethe filled out the rest in a later paper, but I think Weizsäcker only discusses the CN cycle in his paper.  I am presently checking this point, and will consider edits if it's only the CN cycle which is called this.  DAID (talk) 05:00, 14 August 2011 (UTC)

Initial synthesis of C, N & O
Out of interest, can anyone provide more information on where the elements in the CNO cycle come from? There doesn't appear to be any mechanism given in this article on how they're initially generated, and they aren't featured in the p-p chain. Do they then come from the triple alpha process? Thanks in advance --Xanthine 21:35, 29 July 2007 (UTC)


 * Have a look at the pages under "See also" -> Proton-proton chain turns H into He, Triple-alpha process turns He into C, the CNO cycle turns C and H into N, N and H into O and O and H into C and He.
 * — SkyLined (talk) 13:41, 22 April 2009 (UTC)

High incidence of 7N14

 * Is the incidence of 7N14 as an intermediate element in the CNO-1 Nuclear synthesis process supposed to explain the high constituency of 7N14 in the earth's crust makeup? In the CNO formula, it's only an intermediary element and therefor does not increase in constituency. However, a discussion of the process implies an increase in 7N14 to occur as a result of the operation of the process to a condition of "equilibrium". If the process stopped after the 2nd hydrogen addition, we would then be left with a 7N14 atom. Is that what they are talking about.WFPM (talk) 18:22, 10 September 2009 (UTC)

Isotope Notation
Why are the isotopes of C, O, N in equations not given with mass number? This is most unhelpful as it is now. Asgrrr (talk) 08:25, 13 April 2009 (UTC)

Changed the CNO-I passage to show mass numbers. It may not be as visually pleasing, but this is the information that needs to be shown. If physiformulae can't do that then it needs to be discarded. Asgrrr (talk) 13:51, 13 April 2009 (UTC)
 * Please do not make incorrect changes; the notation you used (mass-number bottom-left) is not a scientific notation that I am aware of. Please invest some time into understanding how the templates are used to display elements and how the scientific notations for the elements and their isotopes work. Besides, the formulas that you replaced already contained the mass numbers (top-left of the element symbol), so I do not understand what the problem is you're trying to solve. I've undone your edits.    — SkyLined (talk) 13:40, 22 April 2009 (UTC)

Star mass bounds
"The presence of the heavier elements carbon, nitrogen and oxygen places an upward bound on the maximum size of massive stars to approximately 150 solar masses." This sounds like a very interesting statement. Could someone with the required knowledge add a sentence or two to expand on how the presence of CNO creates an upper bound? --Gargletheape (talk) 19:39, 12 August 2009 (UTC)


 * This statement really needs a reference. I can see how higher rates of energy generation can influence mass loss which can be related to the maximum mass of a star, but we need expansion, clarification, and a reference.  I'm going to add a citation needed tag to this sentence for now.  DAID (talk) 05:18, 14 August 2011 (UTC)

Temperature threshold reference
Will the graph on this page suffice as a reference for the threshold temperature of the CNO cycle? Gizmoguy (talk) 19:11, 2 April 2011 (UTC)


 * The problem for using it as a reference is that these conclusions are model dependent, and while the site is hosted by a university, they don't appear to discuss the model or metallicities used to generate the plot. Of course, most models won't give significantly different results, but the content of CNO seed nuclei surely do influence it, and in fact, this is a point that needs clarification on the article.  For these reasons I don't think it's good enough as a reference for information.  However, it's a nice graph otherwise in terms of the type of graphics we should include, but we need it on wikimedia commons for the copyright issues, as well as to address the issues I note above.  Coincidentally, I already asked my girlfriend tonight for a plot she generated which is similar to that one, which we will be hosting on the commons and posting on this and the pp pages shortly I hope.  As far as a reference, we can probably find something in a textbook pretty easily, so I'll look into that eventually as well.  Granted a textbook may or may not give us the model either, but textbooks are easily valid references.  DAID (talk) 05:16, 14 August 2011 (UTC)

Hot CNO and some needed additions
Tonight I added all the hot CNO reactions as well. I weighed creating a new page rather than adding to this one, but the hot CNO cycle also can use all of the cold CNO reactions, so I decided it made more sense to expand this article instead. But to start with, I just added the reactions and small blurbs for the new sections of Cold and Hot CNO. So some of the introduction material needs to be moved down to the Cold section when it does not apply to the Hot cycles. There is also not yet much information on the Hot CNO cycles. Overall I also think we need some more historical discussions, since originally only the CN cycle was known. A more firm discussion of limiting reactions enters us into the ideas of the later discovered CNO-II, and then CNO-III and CNO-IV networks. And once we get into discussion of limiting reactions, this can feed really nicely into the Hot CNO, where the limiting reactions are different! Happy editing. DAID (talk) 02:30, 15 August 2011 (UTC)

Missing information: Neutrinos
"The neutrinos escape from the star carrying away some energy." This is classical weasel-wording. There should be a statement about the actual amount of energy carried away by Neutrinos. According to Scheffler & Elsässer, 1990, "Physik der Sterne und der Sonne" (physics of the stars and the Sun) it is about 1.7 MeV for CNO-I (I have added the reference there). The book does not give any information about the neutrino energies in the other beta decay reactions.--SiriusB (talk) 20:48, 24 August 2011 (UTC)

HCNO-III (Extraneous text)
Reading through the article I noticed (what appears to be) extraneous text under HCNO-III; as I do not know the purpose behind the text, I have left it alone within the article for someone knowledgeable of this topic to correct:

"...(half-life of 17.22 seconds) **[There was a typo here -- the half-life was listed as 122.24 s, the half-life for oxygen-15; what is the energy output of this particular decay?]"

Cheers -Ham Radio 03:14, 24 February 2012 (UTC) — Preceding unsigned comment added by Ke5skw (talk • contribs)

13N -> 13 C energy: 1,2 vs 2,2 MeV
Article says:

13_7 N 	 	→ 	13_6 C 	+ 	e+ 	+ 	ν_e  + 	1.20 MeV	(half-life of 9.965 minutes)

But An Introduction to Nuclear Astrophysics By Richard N. Boyd (2008) gives 2.220 MeV for this reaction. Same number in ; Nitrogen-13 (ref= Phillips, A.C. (1994). The Physics of Stars. John Wiley & Sons. ISBN 0-471-94057-7.) `a5b (talk) 23:35, 8 January 2013 (UTC) PS: This was changed in diff. `a5b (talk) 23:39, 8 January 2013 (UTC)

Two problems with lede
The lede has, from my viewpoint, two issues:1) Temperature is discussed independently from pressure (density?). I know that both are important for any nuclear chain reaction, so unless pressure (range) is unique for any given Temperature, regardless of the mass of the star (!), then this discussion is just plain inadequate (and misleading). 2) The CNO Cycle is claimed to be both a single thing and yet there are 7 different CNO cycles listed. This makes no sense. There is almost no discussion of when these different mechanisms occur (under what conditions (T, P, and composition)) (or when each peaks, both in absolute terms and in relative terms). 3) One last minor thing: isn't metallicity of the star also important in determining the fusion processes? If so, then that should be mentioned. Clearly it's not just mass, temperature and pressure of a star: metallicity and location (distance from center) are also important (I know they're interrelated).Abitslow (talk) 16:53, 18 June 2016 (UTC)

Incorrect Graphic
The CNO graphic by Antonio Ciccolella has an error. The Alpha particle emitted should be 4He, not 2He. — Preceding unsigned comment added by 73.17.21.109 (talk) 19:22, 2 September 2018 (UTC)

Is this just rank speculation?
I may not be a physicist (or even know the first thing about physics or chemistry or science), but shouldn't a claim this specific have some documented support?

"The Sun has a core temperature of around 15.7×106 K, and only 1.7% of 4 He nuclei produced in the Sun are born in the CNO cycle." Briandrewdrew (talk) 08:28, 3 October 2020 (UTC)

CNO neutrinos confirmed by Borexino
Not much else to add, really;

First Direct Experimental Evidence of CNO neutrinos Borexino Collaboration (2020) https://arxiv.org/pdf/2006.15115.pdf — Preceding unsigned comment added by Ianw16 (talk • contribs) 04:56, 27 November 2020 (UTC)

Nitrogen-15 in CNO-III
When the nucleus becomes nitrogen-15, do we really want to continue the cycle on to oxygen-16 and back to oxygen-17? Nitrogen-15 is back in a stage of the basic CNO cycle (CNO-I) and will follow that the vast majority of the time.

A similar question could be asked with CNO-IV. Johnm307 (talk) 16:47, 21 December 2020 (UTC)