{"paper_id":"1ca3ac2d-6a63-4d8f-bed2-e98b31223859","body_text":"Enhanced 12C(α,γ)16O reaction unveils the formation of single CEMP stars | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Enhanced 12 C(α,γ) 16 O reaction unveils the formation of single CEMP stars Bing Guo, Guangyong Fu, Zhendong An, Shilun Jin This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5605182/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract The chemical abundances of carbon-enhanced metal-poor (CEMP) stars contain plentiful information of the elemental nucleosynthesis in the early universe. Four CEMP-s stars were identified as single stars by monitoring their radial velocities. It hence challenges a longstanding assumption that this type of star is formed in the binary system, where the enriched heavy elements are transferred from the companion. Here, we report an explanation by the influence of the enhanced 12C(α,γ)16O reaction in the nucleosynthesis inside of these single stars themselves, which no longer relies on the transfer of the materials from the companion. This key reaction consumes 12C, and then reduces the amount of neutrons via the neutron source reaction 13C(α,n)16O in which 13C is produced through the proton capture reaction on 12C and the following beta decay of 13N. Therefore, the 12C(α,γ)16O reaction rate affects the evolution of the heavy elements produced by neutron capture reactions of the s-process in asymptotic giant branch (AGB) stars critically. We found that in a sufficiently hot and dense astrophysical environment the 12C(α,γ)16O reaction rate is increased by a factor of 8.1 at typical temperature of 0.1 GK in inner AGB stars and the enhancements even exceed a factor of 10 at higher temperatures due to change of the effective width of the excited state of 16O. Such enhancement suppresses the production of heavy elements formed by the s-process. The resulting suppression of the elements heavier than barium well matches the observations of single CEMP-s stars, thus effectually explains their formation without any companions. The result also convincingly answers the chemical abundances of a CEMP-r+s star, which is a new type of single CEMP star uniquely identified in recent years. The origin of this star, therefore, can be explained by the s-process components produced with the enhanced 12C(α,γ)16O reaction in the AGB phase plus enriched r-process matters from earlier explosive events in the environment. Physical sciences/Physics/Nuclear physics/Nuclear astrophysics Physical sciences/Physics/Astronomy and astrophysics/Stellar evolution Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-5605182\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Physical Sciences - Article\",\"associatedPublications\":[],\"authors\":[{\"id\":398937249,\"identity\":\"5c5df576-33a7-4ff4-acb6-93021e7ad593\",\"order_by\":0,\"name\":\"Bing Guo\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzElEQVRIiWNgGAWjYHACNoYEBgY5BmZStRiTqAUIEhuIVi8fkXzswcMdten97cwPHzDU2DHwzyag2/BGWrpB4pnjuTMOsxkbMBxLZpC4c4CAlhk5ZhKJbcdyNzAzmEkwsB1gMJBIIE5LugEz+/cfDP+I0CIvAdZSk2DAzGPGwNhGhBYDnmdAv7QdMJxxmKdYIrEvmUfiBiFb2pOPPfzZVifP339844cP3+zk+GcQsuUAmDoM4QEV8+BXD7KlAUzVEVQ4CkbBKBgFIxgAAPcBPqBEqvpNAAAAAElFTkSuQmCC\",\"orcid\":\"https://orcid.org/0000-0002-4911-0847\",\"institution\":\"China Institute of Atomic Energy\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Bing\",\"middleName\":\"\",\"lastName\":\"Guo\",\"suffix\":\"\"},{\"id\":398937250,\"identity\":\"69ba6630-5c1f-49ce-a545-7b2e48b3f4c6\",\"order_by\":1,\"name\":\"Guangyong Fu\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"China Institute of Atomic Energy\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Guangyong\",\"middleName\":\"\",\"lastName\":\"Fu\",\"suffix\":\"\"},{\"id\":398937251,\"identity\":\"cb33d1b5-f834-45aa-b5e7-89f4b06934cb\",\"order_by\":2,\"name\":\"Zhendong An\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Institute of Modern Physics, Chinese Academy of Sciences\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Zhendong\",\"middleName\":\"\",\"lastName\":\"An\",\"suffix\":\"\"},{\"id\":398937252,\"identity\":\"790117fe-45bf-4ba6-8231-3b1aa3fb6d9b\",\"order_by\":3,\"name\":\"Shilun Jin\",\"email\":\"\",\"orcid\":\"https://orcid.org/0000-0002-2868-8658\",\"institution\":\"Institute of Modern Physics, Chinese Academy of Sciences\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Shilun\",\"middleName\":\"\",\"lastName\":\"Jin\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2024-12-09 02:35:08\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-5605182/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-5605182/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":74980891,\"identity\":\"a280cbbb-56e8-493e-bde1-69c690e841a6\",\"added_by\":\"auto\",\"created_at\":\"2025-01-29 04:38:44\",\"extension\":\"pdf\",\"order_by\":1,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":856931,\"visible\":true,\"origin\":\"\",\"legend\":\"Article File\",\"description\":\"\",\"filename\":\"main.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5605182/v1_covered_92fe985a-5b8c-4bee-96a1-58a205aff286.pdf\"}],\"financialInterests\":\"There is \\u003cb\\u003eNO\\u003c/b\\u003e Competing Interest.\",\"formattedTitle\":\"\\u003cp\\u003eEnhanced \\u003csup\\u003e12\\u003c/sup\\u003eC(α,γ)\\u003csup\\u003e16\\u003c/sup\\u003eO reaction unveils the formation of single CEMP stars\\u003c/p\\u003e\",\"fulltext\":[],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":false,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":true,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":true,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":true,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"nature-portfolio\",\"isNatureJournal\":true,\"hasQc\":false,\"allowDirectSubmit\":false,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"\",\"title\":\"Nature Portfolio\",\"twitterHandle\":\"\",\"acdcEnabled\":false,\"dfaEnabled\":false,\"editorialSystem\":\"ejp\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false},\"keywords\":\"\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-5605182/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-5605182/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"The chemical abundances of carbon-enhanced metal-poor (CEMP) stars contain plentiful information of the elemental nucleosynthesis in the early universe. Four CEMP-s stars were identified as single stars by monitoring their radial velocities. It hence challenges a longstanding assumption that this type of star is formed in the binary system, where the enriched heavy elements are transferred from the companion. Here, we report an explanation by the influence of the enhanced 12C(α,γ)16O reaction in the nucleosynthesis inside of these single stars themselves, which no longer relies on the transfer of the materials from the companion. This key reaction consumes 12C, and then reduces the amount of neutrons via the neutron source reaction 13C(α,n)16O in which 13C is produced through the proton capture reaction on 12C and the following beta decay of 13N. Therefore, the 12C(α,γ)16O reaction rate affects the evolution of the heavy elements produced by neutron capture reactions of the s-process in asymptotic giant branch (AGB) stars critically. We found that in a sufficiently hot and dense astrophysical environment the 12C(α,γ)16O reaction rate is increased by a factor of 8.1 at typical temperature of 0.1 GK in inner AGB stars and the enhancements even exceed a factor of 10 at higher temperatures due to change of the effective width of the excited state of 16O. Such enhancement suppresses the production of heavy elements formed by the s-process. The resulting suppression of the elements heavier than barium well matches the observations of single CEMP-s stars, thus effectually explains their formation without any companions. The result also convincingly answers the chemical abundances of a CEMP-r+s star, which is a new type of single CEMP star uniquely identified in recent years. 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