Chronos: Towards a self-consistent and absolute stellar age scale. I. A Bayesian hierarchical lithium-age model: Validation on the Pleiades cluster
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arXiv
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| Format: | Preprint |
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2026
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| author | González-Ramírez, L. Barrado, D. Olivares, J. Berihuete, A. Sarro, L. M. Palmero, F. J. |
| author_facet | González-Ramírez, L. Barrado, D. Olivares, J. Berihuete, A. Sarro, L. M. Palmero, F. J. |
| contents | Context. Establishing a self-consistent age scale for stellar populations requires physically well-calibrated chronometers. Among these, lithium-based diagnostics, particularly the lithium depletion boundary (LDB), provide one of the most robust age constraints for stellar populations in the low-mass regime. However, their application is limited by heterogeneous temperature scales and astrophysical dispersion, especially among FGK stars, where rotation can significantly affect lithium abundances.
Aims. As a first step towards a self-consistent age scale, our aim has been to formulate Chronos, the first version of a Bayesian hierarchical lithium-based age-dating model combined with a neural network trained on stellar evolutionary models.
Methods. We implemented a Bayesian hierarchical model that jointly infers stellar effective temperatures, lithium abundances, and the global age of a stellar association. The theoretical LDB is provided by a pre-trained multilayer perceptron based on BT--Settl evolutionary models. The model incorporates a temperature-dependent transition between fully convective ultra-cool dwarfs (UCDs) and FGKM dwarf stars, together with a two-component FGK mixture to account for rotation-induced lithium enhancement. We applied the method to the Pleiades cluster and performed a validation using synthetic datasets.
Results. For the Pleiades cluster, Chronos yields a posterior age distribution centred at $\mathrm{Age}=124.53_{-2.70}^{+3.34}$ Myr, consistent with classical LDB estimates, while simultaneously constraining both global and stellar-level rotation parameters.
Conclusions. This work demonstrates that lithium-based stellar chronology can be recast as a coherent hierarchical inference problem, providing a flexible and statistically robust framework for making age determinations for young (1--600 Myr) stellar populations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_25957 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Chronos: Towards a self-consistent and absolute stellar age scale. I. A Bayesian hierarchical lithium-age model: Validation on the Pleiades cluster González-Ramírez, L. Barrado, D. Olivares, J. Berihuete, A. Sarro, L. M. Palmero, F. J. Solar and Stellar Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics 85A15 (Primary), 85-08 Context. Establishing a self-consistent age scale for stellar populations requires physically well-calibrated chronometers. Among these, lithium-based diagnostics, particularly the lithium depletion boundary (LDB), provide one of the most robust age constraints for stellar populations in the low-mass regime. However, their application is limited by heterogeneous temperature scales and astrophysical dispersion, especially among FGK stars, where rotation can significantly affect lithium abundances. Aims. As a first step towards a self-consistent age scale, our aim has been to formulate Chronos, the first version of a Bayesian hierarchical lithium-based age-dating model combined with a neural network trained on stellar evolutionary models. Methods. We implemented a Bayesian hierarchical model that jointly infers stellar effective temperatures, lithium abundances, and the global age of a stellar association. The theoretical LDB is provided by a pre-trained multilayer perceptron based on BT--Settl evolutionary models. The model incorporates a temperature-dependent transition between fully convective ultra-cool dwarfs (UCDs) and FGKM dwarf stars, together with a two-component FGK mixture to account for rotation-induced lithium enhancement. We applied the method to the Pleiades cluster and performed a validation using synthetic datasets. Results. For the Pleiades cluster, Chronos yields a posterior age distribution centred at $\mathrm{Age}=124.53_{-2.70}^{+3.34}$ Myr, consistent with classical LDB estimates, while simultaneously constraining both global and stellar-level rotation parameters. Conclusions. This work demonstrates that lithium-based stellar chronology can be recast as a coherent hierarchical inference problem, providing a flexible and statistically robust framework for making age determinations for young (1--600 Myr) stellar populations. |
| title | Chronos: Towards a self-consistent and absolute stellar age scale. I. A Bayesian hierarchical lithium-age model: Validation on the Pleiades cluster |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics 85A15 (Primary), 85-08 |
| url | https://arxiv.org/abs/2605.25957 |