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| Natura: | Preprint |
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2025
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| Accesso online: | https://arxiv.org/abs/2512.06069 |
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| author | Redai, Jéa Adams Chandra, Vedant Yee, Samuel W. DiTomasso, Victoria Andrews, Sean Öberg, Karin Woody, Rebecca Latham, David W. Bieryla, Allyson Quinn, Samuel N. Charbonneau, David Carmichael, Theron W. Hsu, Chih-Chun Vowell, Noah Wang, Jason J. Zieba, Sebastian Benni, Paul Collins, Karen A. Ciardi, David R. van Eyken, Julian Fong, William Lund, Michael B. Tatarnikov, Andrei M. |
| author_facet | Redai, Jéa Adams Chandra, Vedant Yee, Samuel W. DiTomasso, Victoria Andrews, Sean Öberg, Karin Woody, Rebecca Latham, David W. Bieryla, Allyson Quinn, Samuel N. Charbonneau, David Carmichael, Theron W. Hsu, Chih-Chun Vowell, Noah Wang, Jason J. Zieba, Sebastian Benni, Paul Collins, Karen A. Ciardi, David R. van Eyken, Julian Fong, William Lund, Michael B. Tatarnikov, Andrei M. |
| contents | We report the discovery of TOI-7019b, the first transiting brown dwarf (BD) known to orbit a star that is part of the Milky Way's ancient thick disk, as defined chemically ([Fe/H] $= -0.79 \pm 0.05$ dex, [$α$/Fe] $= +0.26 \pm 0.05$ dex, [M/H] $= -0.59 \pm 0.06$ dex) and kinematically ($v_{\perp} \approx 150 \pm 1$ km s$^{-1}$). We estimate a system age $τ= 12 \pm 2$ Gyr by fitting the host star's spectrum and spectral energy distribution to alpha-enhanced isochrones, and independently using the age-metallicity relation of the thick disk. This makes TOI-7019 by far the most metal-poor and ancient BD host known to date. We measure a BD mass of $61.3 \pm 2.1$ $M_{\rm J}$ and radius of $0.82 \pm 0.02$ $R_{\rm J}$ from a joint analysis of transit photometry and radial velocity measurements, along with an orbital period of $48.2592 \pm 0.0001$ days and an orbital eccentricity of $0.403 \pm 0.002$. The measured radius appears $12.3\% \pm 2.8\%$ larger than predicted relative to standard evolutionary models for old, metal-poor brown dwarfs, hinting at missing physics like the magnetic inhibition of convection. TOI-7019b lowers the probed metallicity regime for transiting BDs by over a factor of two, making it a benchmark system to test evolutionary models in the low-metallicity regime. Future measurements of TOI-7019b's atmosphere will test whether a brown dwarf's atmospheric composition tracks its host star's abundances, as expected for binary-like co-formation. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_06069 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An Ancient Brown Dwarf Transiting a Metal-Poor Thick Disk Star Redai, Jéa Adams Chandra, Vedant Yee, Samuel W. DiTomasso, Victoria Andrews, Sean Öberg, Karin Woody, Rebecca Latham, David W. Bieryla, Allyson Quinn, Samuel N. Charbonneau, David Carmichael, Theron W. Hsu, Chih-Chun Vowell, Noah Wang, Jason J. Zieba, Sebastian Benni, Paul Collins, Karen A. Ciardi, David R. van Eyken, Julian Fong, William Lund, Michael B. Tatarnikov, Andrei M. Earth and Planetary Astrophysics Solar and Stellar Astrophysics We report the discovery of TOI-7019b, the first transiting brown dwarf (BD) known to orbit a star that is part of the Milky Way's ancient thick disk, as defined chemically ([Fe/H] $= -0.79 \pm 0.05$ dex, [$α$/Fe] $= +0.26 \pm 0.05$ dex, [M/H] $= -0.59 \pm 0.06$ dex) and kinematically ($v_{\perp} \approx 150 \pm 1$ km s$^{-1}$). We estimate a system age $τ= 12 \pm 2$ Gyr by fitting the host star's spectrum and spectral energy distribution to alpha-enhanced isochrones, and independently using the age-metallicity relation of the thick disk. This makes TOI-7019 by far the most metal-poor and ancient BD host known to date. We measure a BD mass of $61.3 \pm 2.1$ $M_{\rm J}$ and radius of $0.82 \pm 0.02$ $R_{\rm J}$ from a joint analysis of transit photometry and radial velocity measurements, along with an orbital period of $48.2592 \pm 0.0001$ days and an orbital eccentricity of $0.403 \pm 0.002$. The measured radius appears $12.3\% \pm 2.8\%$ larger than predicted relative to standard evolutionary models for old, metal-poor brown dwarfs, hinting at missing physics like the magnetic inhibition of convection. TOI-7019b lowers the probed metallicity regime for transiting BDs by over a factor of two, making it a benchmark system to test evolutionary models in the low-metallicity regime. Future measurements of TOI-7019b's atmosphere will test whether a brown dwarf's atmospheric composition tracks its host star's abundances, as expected for binary-like co-formation. |
| title | An Ancient Brown Dwarf Transiting a Metal-Poor Thick Disk Star |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2512.06069 |