V3101 Cyg: A Cataclysmic Variable Born with a Brown Dwarf Donor

V3101 Cyg: A Cataclysmic Variable Born with a Brown Dwarf Donor | 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 Article V3101 Cyg: A Cataclysmic Variable Born with a Brown Dwarf Donor Sergio Ramirez, Boris Gänsicke, Snehalata Sahu, Diogo Belloni, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8079157/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 Cataclysmic variables descending from detached brown dwarf plus white dwarf binaries have long been predicted but none have been found so far. We report here on a system whose origin is best explained by said scenario: V3101 Cyg. We measured a white dwarf mass of Mwd = 0.47 ± 0.01 M⊙ from the analysis of far-ultraviolet HST spectroscopy which, combined with the published mass ratio of q = Mbd/Mwd = 0.088, implies a donor star mass of Mbd = 0.041 M⊙, well below the hydrogen burning limit. This makes V3101 Cyg the only known object composed of both a low-mass white dwarf and a substellar companion. We modelled the past evolution of this system using MESA, and find that the standard cataclysmic variable evolutionary channel fails to reproduce the donor’s estimated mass and radius, as well as the low quiescent temperature of both components – measured from archival photometry taken before the system experienced a ≃9.5 mag outburst in 2019. In contrast, the observed characteristics of V3101 Cyg can be well reproduced in MESA by progenitors born with a brown dwarf companion. Based on our results, V3101 Cyg represents the first unambiguous observational confirmation of the brown dwarf plus white dwarf evolutionary channel, and provides a first opportunity to quantitatively test the predictions of close binary population models Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stars Physical sciences/Astronomy and planetary science/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. 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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-8079157","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":553589031,"identity":"ad0db788-fc22-4e3f-b507-3092b625e7a6","order_by":0,"name":"Sergio 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We report here on a system whose origin is best explained by said scenario: V3101 Cyg.\r\nWe measured a white dwarf mass of Mwd = 0.47 ± 0.01 M⊙ from the analysis of far-ultraviolet HST spectroscopy which,\r\ncombined with the published mass ratio of q = Mbd/Mwd = 0.088, implies a donor star mass of Mbd = 0.041 M⊙, well\r\nbelow the hydrogen burning limit. This makes V3101 Cyg the only known object composed of both a low-mass white\r\ndwarf and a substellar companion. We modelled the past evolution of this system using MESA, and find that the\r\nstandard cataclysmic variable evolutionary channel fails to reproduce the donor’s estimated mass and radius, as\r\nwell as the low quiescent temperature of both components – measured from archival photometry taken before the\r\nsystem experienced a ≃9.5 mag outburst in 2019. In contrast, the observed characteristics of V3101 Cyg can be well\r\nreproduced in MESA by progenitors born with a brown dwarf companion. Based on our results, V3101 Cyg represents\r\nthe first unambiguous observational confirmation of the brown dwarf plus white dwarf evolutionary channel, and\r\nprovides a first opportunity to quantitatively test the predictions of close binary population models","manuscriptTitle":"V3101 Cyg: A Cataclysmic Variable Born with a Brown Dwarf Donor","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-02 15:03:44","doi":"10.21203/rs.3.rs-8079157/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-astronomy","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natastron","sideBox":"Learn more about [Nature Astronomy](http://www.nature.com/natastron/)","snPcode":"","submissionUrl":"","title":"Nature Astronomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2cab60f9-b714-43e3-ac05-450934a06de1","owner":[],"postedDate":"December 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":58907673,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stars"},{"id":58907674,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution"}],"tags":[],"updatedAt":"2026-01-09T15:37:20+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-02 15:03:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8079157","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8079157","identity":"rs-8079157","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}