Stellar Ages of M Dwarf Hosts of Temperate Sub-Neptunes
Abstract
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.
Related
- Tracking the evolution of sub-Neptunes. II. The radius valley on gyrochronological ages
- The Pandora project. II: how non-thermal physics drives bursty star formation and temperate mass-loaded outflows in dwarf galaxies
- Beyond gas dwarfs and water worlds: hybrid envelopes among the M-dwarf sub-Neptunes characterised with JWST
- Stellar masses and ages in Gaia Data Release 4 from the Final Luminosity Age Mass Estimator algorithm
- Towards breaking the degeneracy between stellar ages and unresolved multiplicity
BibTeX
@misc{sairam2026stellar,
title = {{Stellar Ages of M Dwarf Hosts of Temperate Sub-Neptunes}},
author = {Lalitha Sairam and Nikku Madhusudhan},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17505},
eprint = {2609.17505},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17505},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Stellar Ages of M Dwarf Hosts of Temperate Sub-Neptunes
AU - Lalitha Sairam
AU - Nikku Madhusudhan
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17505
UR - https://arxiv.org/abs/2609.17505
AB - 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.
ER -