# The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equivalent widths (EAGLES)

**Authors:** R. D. Jeffries, R. J. Jackson, Nicholas J. Wright, G. Weaver, G. Gilmore, S. Randich, A. Bragaglia, A. J. Korn, R. Smiljanic, K. Biazzo, A. R. Casey, A. Frasca, A. Gonneau, G. Guiglion, L. Morbidelli, L. Prisinzano, G. G. Sacco, G. Tautvaišienė, C. C. Worley, S. Zaggia  
**arXiv:** [2304.12197](https://arxiv.org/abs/2304.12197)  
**Date:** 2023-04-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.12197v1/

## Key points

- The Gaia-ESO survey has presented an empirical model for age-dependent photospheric lithium depletion.
- The model was calibrated using a sample of 6200 stars in 52 open clusters with ages ranging from 2 to 6000 million years and metallicities between $-0.3$ and $0.2$.
- The model can be used to obtain age estimates and posterior age probability distributions from measurements of the Li I 6708A equivalent width for individual (pre) main sequence stars with effective temperatures between 3000 K and 6500 K.
- This method is particularly useful as determining the age of such stars using the HR diagram can be highly model-dependent or insensitive.
- The method has achieved precisions of up to 0.1 dex in log age, with even higher precision possible when combining individual age probabilities of coeval groups and associations.
- It was validated on a sample of exoplanet-hosting young stars, finding agreement with claimed young ages for some but not others.
- For seven well-studied young moving groups, better than 10% precision in age was obtained along with excellent agreement with published ages.
- The derived ages for young clusters ($<1$ Gyr) were found to be consistent with several published, model-insensitive lithium depletion boundary ages.
- However, there remain systematic age errors that could be as large as a factor of two for older clusters.
- There is no evidence linking these errors to any strong systematic metallicity dependence of (pre) main sequence lithium depletion within the range $-0.29 < {\rm [Fe/H]} < 0.18$.
- The methods and model are provided as software called "Empirical AGes from Lithium Equivalent widthS" (EAGLES).

## Summary

The Gaia-ESO survey has presented an empirical model for age-dependent photospheric lithium depletion that has been calibrated using a sample of 6200 stars in 52 open clusters. The stars have ages ranging from 2 to 6000 million years and metallicities between $-0.3$ and $0.2$. This model can be used to obtain age estimates and posterior age probability distributions from measurements of the Li I 6708A equivalent width for individual (pre) main sequence stars with effective temperatures between 3000 K and 6500 K. This is particularly useful as determining the age of such stars using the HR diagram can be highly model-dependent or insensitive. The method has achieved precisions of up to 0.1 dex in log age, with even higher precision possible when combining individual age probabilities of coeval groups and associations. It was validated on a sample of exoplanet-hosting young stars, finding agreement with claimed young ages for some but not others. For seven well-studied young moving groups, better than 10% precision in age was obtained along with excellent agreement with published ages. The derived ages for young clusters ($<1$ Gyr) were also found to be consistent with several published, model-insensitive lithium depletion boundary ages. However, there remain systematic age errors that could be as large as a factor of two for older clusters. There is no evidence linking these errors to any strong systematic metallicity dependence of (pre) main sequence lithium depletion within the range $-0.29 < {\rm [Fe/H]} < 0.18$. The methods and model are provided as software called "Empirical AGes from Lithium Equivalent widthS" (EAGLES).