Zeeman Doppler Imaging of $τ$Ceti: The Weakest Magnetic Field Detected in a Sun-like Star
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| Format: | Preprint |
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2025
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| _version_ | 1866916950667427840 |
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| author | Chiti, Federica Kochukhov, Oleg van Saders, Jennifer L. Metcalfe, Travis S. |
| author_facet | Chiti, Federica Kochukhov, Oleg van Saders, Jennifer L. Metcalfe, Travis S. |
| contents | For nearly a decade, observations have shown that many older Sun-like stars spin faster than predicted, a phenomenon known as weakened magnetic braking (WMB). The leading hypothesis for WMB is a weakening of the large-scale dipole field, which leads to a less efficient angular momentum loss. To test this hypothesis on a star known to be in the WMB regime, we present the first Zeeman Doppler Imaging (ZDI) map of the Sun-like star $τ$Ceti, reconstructed using spectropolarimetric data from the Canada-France-Hawai'i Telescope (CFHT). Our ZDI analysis reveals a remarkably simple, stable and weak ($\langle B\rangle =0.17 \mathrm{G}$) magnetic field, characterized by a predominantly dipolar ($\sim92\%$ magnetic energy contained in $l=1$ modes), and highly axisymmetric ($\sim88\%$ magnetic energy contained in $m<l/2$ modes) morphology. We infer a dipole field strength of $B_{\mathrm{dip}}=0.31 \mathrm{G}$, nearly an order of magnitude weaker than standard braking model predictions, providing direct confirmation of the weakened large-scale dipole predicted by the WMB hypothesis. This work establishes a new benchmark for ZDI, demonstrating that even extremely quiet stars in the WMB regime are accessible to this technique. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_12310 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Zeeman Doppler Imaging of $τ$Ceti: The Weakest Magnetic Field Detected in a Sun-like Star Chiti, Federica Kochukhov, Oleg van Saders, Jennifer L. Metcalfe, Travis S. Solar and Stellar Astrophysics For nearly a decade, observations have shown that many older Sun-like stars spin faster than predicted, a phenomenon known as weakened magnetic braking (WMB). The leading hypothesis for WMB is a weakening of the large-scale dipole field, which leads to a less efficient angular momentum loss. To test this hypothesis on a star known to be in the WMB regime, we present the first Zeeman Doppler Imaging (ZDI) map of the Sun-like star $τ$Ceti, reconstructed using spectropolarimetric data from the Canada-France-Hawai'i Telescope (CFHT). Our ZDI analysis reveals a remarkably simple, stable and weak ($\langle B\rangle =0.17 \mathrm{G}$) magnetic field, characterized by a predominantly dipolar ($\sim92\%$ magnetic energy contained in $l=1$ modes), and highly axisymmetric ($\sim88\%$ magnetic energy contained in $m<l/2$ modes) morphology. We infer a dipole field strength of $B_{\mathrm{dip}}=0.31 \mathrm{G}$, nearly an order of magnitude weaker than standard braking model predictions, providing direct confirmation of the weakened large-scale dipole predicted by the WMB hypothesis. This work establishes a new benchmark for ZDI, demonstrating that even extremely quiet stars in the WMB regime are accessible to this technique. |
| title | Zeeman Doppler Imaging of $τ$Ceti: The Weakest Magnetic Field Detected in a Sun-like Star |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2509.12310 |