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Topic: CNO cycle

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	CNO cycle
		The CNO (carbon-nitrogen-oxygen) cycle is one of two fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain.
		While the proton-proton chain is more important in stars the size of the sun or less, theoretical models show that the CNO cycle is the dominant source of energy in heavier stars.
		The CNO cycle may also be the dominant cause of nitrogen and oxygen production.
	www.ebroadcast.com.au /lookup/encyclopedia/cn/CNO_cycle.html (116 words)

	CNO cycle - Wikipedia, the free encyclopedia
		The CNO cycle (for carbon-nitrogen-oxygen), or sometimes Bethe-Weizsäcker-cycle, is one of two fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain.
		The main branch of the CNO cycle is known as CNO-I, the minor branch as CNO-II.
		While the total number of "catalytic" CNO nuclei is conserved in the cycle, in stellar evolution the relative proportions of the nuclei are altered.
	en.wikipedia.org /wiki/CNO_cycle (415 words)

	The CNO Cycle (Site not responding. Last check: 2007-10-12)
		The mass-15 isotope of Nitrogen captures a proton and emits an alpha-particle (that is, a nucleus of helium) to close the cycle and return to C-12.
		The net effect of the CNO cycle is to convert hydrogen to helium (the alpha particle emitted in the last step).
		As for the PP chain, the energy released in the CNO cycle is contained in the energy of the particles and gamma-rays produced in the steps of the cycle.
	csep10.phys.utk.edu /astr162/lect/energy/cno.html (397 words)

	SUN
		The p-p chain and the CNO cycle are shown in Table 1-3; there the third column indicates the percentage of the solar terminations of the p-p chain in each reaction.
		At the present stage in the evolution of the Sun, the CNO cycle is believed to play a rather small role in the energy and neutrino production budget (Bahcall 1989).
		N (in the case of the CNO cycle).
	www.columbia.edu /~ah297/unesa/sun/sun-chapter4.html (554 words)

	The main sequence (MS) phase
		This is the important part of the cycle with respect to low- and intermediate-mass stars, since the temperatures required to allow the ON part of the cycle to operate are only expected for quite massive stars.
		This is one of the characteristics of the CN cycles.
		The full CNO cycle can come into operation for sufficiently high masses (leading to the eventual conversion of oxygen into nitrogen) but is not usually relevant to the low and intermediate mass stars considered here.
	www.missouri.edu /~speckan/witch-stuff/Research/chapter2/node10.html (300 words)

	Nuclear Energy
		(CNO stands for Carbon, Nitrogen, Oxygen.) In the CNO cycle, a carbon nucleus acts as a catalyst for the conversion of hydrogen into helium.
		During the course of the CNO cycle, the carbon nucleus is converted into a nitrogen nucleus and an oxygen nucleus, but in the end, emerges unscathed.
		THE BOTTOM LINE is the same for both the proton-proton chain and the CNO cycle: four hydrogen nuclei are fused together into a single helium nucleus.
	www.stormpages.com /swadhwa/stellarevolution/lecture11.htm (1048 words)

	The Astrophysics Spectator: The CNO Hydrogen Fusion Simulator
		The CNO fusion simulator shows the binary fusion processes of the CNO cycles.
		The simulator follows the nuclear fusion of hydrogen into helium-4 in a gas composed of hydrogen, helium, and isotopes of carbon, nitrogen, and oxygen under the condition that both the temperature and the nucleon density of the gas are constant.
		The “Processes” plot shows the relative contribution to the creation of helium-4 of the CNO 1 and CNO 2 cycles; the sum of these values is normalized to 1.
	www.astrophysicsspectator.com /topics/stars/FusionHydrogenCNOSim.html (745 words)

	Stellar Evolution: Main Sequence
		CNO are much larger atoms than H or He and can form into various isotopes.
		The CNO cycle is basically the fusion of protons by carbon-12 nuclei until they work their way up the periodic table to nitrogen-15 where the fusion of a proton produces a He nuclei and carbon-12 (back to start).
		Notice that the number of CNO atoms does not change during the cycle, it serves to only convert 4 protons into one He nuclei.
	zebu.uoregon.edu /~js/ast122/lectures/lec14.html (1312 words)

	Competition between the P-P Chain and the CNO Cycle (Site not responding. Last check: 2007-10-12)
		First, there must be C, N, or O present for the CNO cycle to occur, so it can only happen for stars where this is true.
		This is why the CNO cycle is more important for heavier stars: their interior temperatures are higher, thus favoring the CNO cycle.
		In the case of the Sun, detailed considerations suggest that it is producing about 98-99% of its energy from the PP chain and only about 1% from the CNO cycle.
	csep10.phys.utk.edu /astr162/lect/energy/cno-pp.html (254 words)

	Carbon Cycle of Nuclear Fusion
		The main theme of the carbon cycle is the adding of protons, but after a carbon-12 nucleus fuses with a proton to form nitrogen-13, one of the protons decays with the emission of a positron and a neutrino to form carbon -13.
		This last reaction is the main source of energy in the cycle for the fueling of the star.
		While this process is not a significant part of the sun's fuel cycle, a star like Sirius with somewhat more than twice the mass of the sun derives almost all of its power from the carbon cycle.
	hyperphysics.phy-astr.gsu.edu /hbase/astro/carbcyc.html (312 words)

	Fusion: Hey! Remember the Sun? Energy producing reactions within stars...
		he CNO cycle is another sequence of energy producing reactions, which ultimately results in the conversion of hydrogen to helium.
		Current estimates say the Sun produces 98-99% of its energy through the proton-proton reaction and 1% from the CNO cycle.
		However, the CNO cycle would be the major energy producer if our Sun was 10-20% more massive.
	library.thinkquest.org /17940/texts/ppcno_cycles/ppcno_cycles.html (888 words)

	#1 Site For Learning Science
		There are two basic cycles is which such fusion reactions can take place; one is called the proton-proton cycle and the second process is called the carbon-carbon cycle (or the CNO cycle).
		This is the reason why this cycle is known as carbon-carbon cycle or CNO cycle.
		The outcome of the carbon-carbon cycle is same as the proton-proton cycle, but at times it tends to produce higher elements also.
	home.att.net /~cat4a/nuclear_VII.htm (866 words)

	Stars may be older than we think (May 2004) - News - PhysicsWeb
		The results suggest that the cross-section for a crucial reaction in the carbon-nitrogen-oxygen (CNO) cycle inside stars is two times slower than the values used in current models (Physics Letters B to be published).
		The slowest reaction in the CNO cycle is the fusion of a proton with a nitrogen-14 nucleus to produce oxygen-15 and a gamma-ray.
		The age of the oldest stars in the universe -- those that form globular star clusters -- is calculated by analysing their light spectra using current values for the rate of the CNO cycle.
	www.physicsweb.org /articles/news/8/5/11/1 (435 words)

	Astronomy Supplement - Life and Birth of Stars
		For a star of 10M., the average rate of energy generation, supplied principally by the CNO cycle, is about 1000 times greater than that of the Sun.
		The other hydrogen-burning reaction, the CNO cycle, has six steps occurring at rates between 80 seconds and 300 million years but leading to the same result as the p-p chain; that is, the conversion of four protons to produce one helium nucleus and to liberate energy.
		The CNO cycle in massive stars also depends more strongly on temperature and consumes hydrogen faster than does the p-p chain that operates in low-mass stars.
	physics.gmu.edu /~jevans/astr103/CourseNotes/ECText/ch17_txt.htm (7266 words)

	Nuclei prompt stellar rethink (December 2001) - Physics World - PhysicsWeb
		The second process, known as the CNO cycle, is not important in the Sun but it does dominate heavier stars.
		The net result of this cycle is the conversion of hydrogen to helium, with the carbon nuclei simply acting as catalysts.
		One of the slowest reactions in the CNO cycle is the fusion of protons with nitrogen-14 nuclei to produce oxygen-15.
	physicsweb.org /article/world/14/12/3 (1275 words)

	Fusion
		However, von Weizsäcker did not investigate the rate at which energy would be produced in a star by the CNO cycle nor did he study the crucial dependence upon stellar temperature.
		The CNO cycle, the second process which was also considered by von Weizsäcker, is most important in stars that are more massive than the sun.
		W.A. Fowler, Willy as he was universally known, led a team of colleagues in his Caltech Kellogg Laboratory and inspired physicists throughout the world to measure or calculate the most important details of the p-p chain and the CNO cycle.
	nobelprize.org /nobel_prizes/physics/articles/fusion/sun_4.html (965 words)

	CNO bi-cycle concept from the Astronomy knowledge base (Site not responding. Last check: 2007-10-12)
		CNO bi-cycle concept from the Astronomy knowledge base
		This reaction occurs once in about 2000 CN cycles.
		For main-sequence stars greater than a few solar masses, hydrogen burning by the CNO bi-cycle is the main source of energy.
	www.site.uottawa.ca:4321 /astronomy/CNObi-cycle.html (109 words)

	The origin of the elements of life
		Both helium "burning" alpha-capture reactions, and CNO cycles of proton capture will occur at shell-like regions with the appropriate conditions within the star.
		Towards the end of their brief lives very strong winds of gas are driven off the surfaces of massive stars, reducing their mass and revealing the layers deep inside the star where the products of the recent nuclear reactions can be seen.
		Their element production can again be by CNO processing to produce nitrogen (from the C or O seed) and - in their later life as giant stars - alpha-capture reactions.
	www.europhysicsnews.com /full/14/article1/article1.html (2954 words)

	CERN Courier - Neutrinos limit role of CNO - IOP Publishing - article
		The two main sets of reactions are the p-p chain, which involves the lightest nuclei, and the CNO cycle, in which the heavier nuclei of carbon, nitrogen and oxygen play a role.
		Indeed, before the data from the Sudbury Neutrino Observatory (SNO) and SuperKamiokande became available, calculations in which the CNO cycle contributed as much as 99.95% of the solar energy would fit the data.
		Their best fit indicates that the energy from the CNO cycle must be less than 7.3% at the 3ρ level.
	cerncourier.com /main/article/43/4/4 (352 words)

	CNO Cycle (Site not responding. Last check: 2007-10-12)
		In the CNO cycle, Carbon acts simply as a catalyst for the reactions.
		The CNO cycle operates in stars slightly more massive than the Sun.
		Well, note that the initial reaction involves a carbon nucleus (with 6 protons) and a hydrogen nucleus (1 proton).
	zebu.uoregon.edu /~imamura/208/feb6/CNO.html (152 words)

	Notes to Unit 2
		N created by the last step of the second cycle feeds back into the main CNO cycle in the middle.
		For example, CNO fusion accounts for only about 2% of the energy generated in the Sun's core when averaged over the entire nuclear burning region.
		However, because CNO is more sensitive to temperature than PP, while both grow in strength as temperature increases, the CNO reaction rate grows stronger faster, and eventually surpasses PP as the main contributor to the total fusion energy output of the core.
	www-astronomy.mps.ohio-state.edu /~pogge/Ast162/Unit2/notes.html (918 words)

	CNO cycle
		The title of your topic and its context suggests that you are i nterested in the carbon nitrogen oxygen cycle of helium nucleosysnthesis in stars.
		Giving them a lecture on helioseismology in response to a question about the CNO cycle is probably not very helpful.
		My first post was straightforward and mainly pointed out that CNO or PP, either method causes the H2 fusion and that stars are always fluctuating/pulsating/changing.
	www.physicsforums.com /showthread.php?t=109269 (4056 words)

	Astrophysics and Space Physics: Thermonuclear Reaction Rates in Stars
		These latter two are part of the proton-proton chain of hydrogen-burning reactions in solar-type stars, while the first is part of the CNO cycle.
		The competition between the proton-proton reaction and CNO cycle for the destruction of
		The reaction rates that take place in the CNO bi-cycle are illustrated in Fig.
	www.llnl.gov /science_on_lasers/07AstSpace/AS-F_Ther.html (1046 words)

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