![Log–log relation between age and rotation period for M dwarfs. Black squares show the Engle & Guinan (2023) sample. Filled circles are cluster members from Curtis et al. (2020) and Godoy-Rivera et al. (2021), colour-coded by spectral type (M2–M6). The solid blue curve is the median fit. Dark- and light-grey bands denote the 68% and 95% posterior predictive regions, including intrinsic astrophysical scatter. Triangles with error bars indicate the target stars analysed in this work. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/Stellar.png?fit=1200%2C676&ssl=1)
[astro-ph.EP] Measuring M dwarf ages is a central challenge in stellar astrophysics. These stars evolve so slowly that isochrone fitting gives little constraint, requiring alternative methods based on rotation, activity, and kinematics.
Reliable ages help constrain the formation and evolution of planetary systems around M dwarfs, including the temperate sub-Neptunes now being characterised with the James Webb Space Telescope (JWST). We present an age analysis of six nearby M dwarf planet hosts (TOI-732, TOI-736, TOI-270, TOI-1468, TOI-1231, and K2-18) using lithium absorption at 6708 Å, rotation periods, and Galactic kinematics.
The Li I 6708 Åfeature is absent above 3σ in all targets, implying substantial depletion and ages exceeding 200 Myr. Rotation periods of 39-145 days yield ages of 2.8-8.6 Gyr, calibrated against open cluster M dwarfs and including the intrinsic dispersion of the rotation-age relation. Kinematic ages span 0.8-13 Gyr with uncertainties of 4-6 Gyr.
These are less precise per star but help identify outliers such as TOI-1231 (~13 Gyr) and K2-18 ( ~1-2 Gyr) and place the stars in Galactic context. Rotation yields age constraints 2-6 times tighter than kinematics where periods are measured, and comparable constraints where periods must be inferred from chromospheric activity.
Combining multiple indicators enables more secure classification of these stars’ evolutionary states, providing reference points for future comparative studies.
Lalitha Sairam, Nikku Madhusudhan
Comments: 12 pages, 9 Figures, accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2609.17505 [astro-ph.EP] (or arXiv:2609.17505v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.17505
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Submission history
From: Sairam Lalitha
[v1] Tue, 15 Sep 2026 17:44:39 UTC (4,103 KB)
https://arxiv.org/abs/2609.17505
Astrobiology,
