A Systematic Trend in the Observed vs. Predicted Radii of Transiting Brown Dwarfs

[2607.27352] A Systematic Trend in the Observed vs. Predicted Radii of Transiting Brown Dwarfs Skip to main content Search Submit Donate Log in Astrophysics > Earth and Planetary Astrophysics arXiv:2607.27352 (astro-ph) [Submitted on 29 Jul 2026 ( v1 ), last revised 27 Aug 2026 (this version, v2)] Title: A Systematic Trend in the Observed vs. Predicted Radii of Transiting Brown Dwarfs Authors: Thomas G. Beatty View PDF HTML (experimental) Abstract: Transiting brown dwarfs provide a direct empirical test of substellar evolutionary models, and with more than 50 now known we can carry out this test at the population level. We compared the observed masses and radii of 31 field-age, weakly irradiated transiting brown dwarfs to the Sonora Diamondback, Sonora Bobcat, and ATMO 2020 grids, and a subset of 23 of them to the irradiated models of Mukherjee et al. (2026). In every comparison we find a radius-dependent trend, with fits of $R_{\rm pred}$ versus $R_{\rm obs}$ yielding slopes of $0.3{-}0.4$, shallower than the one-to-one relation at $3.7{-}8\sigma$. The mean inflation is $5{-}14\%$ depending on the grid, reaching $\sim20\%$ among the largest objects. We also measure an intrinsic dispersion of $8{-}12\%$, two to three times the measurement uncertainty. While the mean inflation offset varies by a factor of three among grids, this dispersion does not, indicating that it is a property of the population and not the models. We find no correlation with mass, equilibrium temperature, orbital separation, tidal heating rate, or age, and only a marginal ($1.7\sigma$) trend with host-star metallicity. Most notable is the absence of any trend with irradiation, which argues against hot Jupiter-like stellar heating as the primary cause. We instead suggest that brown dwarfs span a wider range of atmospheric boundary conditions than current grids represent. The brown dwarf radius inflation is comparable to that in fully convective M dwarfs, and it is likely the transiting counterpart to the luminosity discrepancies seen in dynamical-mass benchmarks. If the trend extends below the deuterium-burning limit, it would bias directly imaged planet mass estimates, overestimating luminosity-age masses by several to ten percent and requiring spectroscopic-gravity masses to be revised upward by $\sim20{-}45\%$. Comments: 21 pages, 11 figures, 2 tables. Submitted to AAS journals; updated based on referee's comments Subjects: Earth and Planetary Astrophysics (astro-ph.EP) ; Solar and Stellar Astrophysics (astro-ph.SR) Cite as: arXiv:2607.27352 [astro-ph.EP] (or arXiv:2607.27352v2 [astro-ph.EP] for this version) https://doi.org/10.48550/arXiv.2607.27352 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Thomas Beatty [ view email ] [v1] Wed, 29 Jul 2026 18:09:11 UTC (3,544 KB) [v2] Thu, 27 Aug 2026 20:13:14 UTC (3,544 KB) Full-text links: Access Paper: View PDF HTML (experimental) TeX Source view license Current browse context: astro-ph.EP < prev | next > new | recent | 2026-07 Change to browse by: astro-ph astro-ph.SR References & Citations NASA ADS Google Scholar Semantic Scholar export BibTeX citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer ( What is the Explorer? ) Connected Papers Toggle Connected Papers ( What is Connected Papers? ) Litmaps Toggle Litmaps ( What is Litmaps? ) scite.ai Toggle scite Smart Citations ( What are Smart Citations? ) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv ( What is alphaXiv? ) Links to Code Toggle CatalyzeX Code Finder for Papers ( What is CatalyzeX? ) DagsHub Toggle DagsHub ( What is DagsHub? ) GotitPub Toggle Gotit.pub ( What is GotitPub? ) Huggingface Toggle Hugging Face ( What is Huggingface? ) ScienceCast Toggle ScienceCast ( What is ScienceCast? ) Demos Demos Replicate Toggle Replicate ( What is Replicate? ) Spaces Toggle Hugging Face Spaces ( What is Spaces? ) Spaces Toggle TXYZ.AI ( What is TXYZ.AI? ) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower ( What are Influence Flowers? ) Core recommender toggle CORE Recommender ( What is CORE? ) IArxiv recommender toggle IArxiv Recommender ( What is IArxiv? ) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them. Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs . Which authors of this paper are endorsers? | Disable MathJax ( What is MathJax? ) We gratefully acknowledge support from our major funders , member institutions , and all contributors. About · Help · Contact · Subscribe · Copyright · Privacy · Accessibility · Operational Status (opens in new tab) Major funding support from

Related documents

• A Systematic Trend in the Observed vs. Predicted Radii of Transiting Brown Dwarfs#682782
• Euclid: Early Release Observations -- Internal kinematics and the convective-transition gap of NGC 6397. High-precision multiple-pass photometry and astrometry#284174
• Using Old and New Approaches: Determining Physical Properties of Brown Dwarfs with Empirical Relations and Machine Learning Models#1122867
• Electromagnetic Counterparts of Stellar-mass Binary Black Hole Mergers in AGN Accretion Disks: Theoretical Models and Observational Status#1144191
• The dynamical environment of the high-mass star-forming region G28.288$-$0.364#1014768