The Gaia-ESO survey: a lithium depletion boundary age for NGC 2232

Astrometry and photometry from Gaia and spectroscopic data from the Gaia-ESO Survey (GES) are used to identify the lithium depletion boundary (LDB) in the young cluster NGC 2232. A specialized spectral line analysis procedure was used to recover the signature of undepleted lithium in very low luminosity cluster members. An age of 38 +/- 3 Myr is inferred by comparing the LDB location in absolute colour-magnitude diagrams (CMDs) with the predictions of standard models. This is more than twice the age derived from fitting isochrones to low-mass stars in the CMD with the same models. Much closer agreement between LDB and CMD ages is obtained from models that incorporate magnetically suppressed convection or flux-blocking by dark, magnetic starspots. The best agreement is found at ages of 45-50 Myr for models with high levels of magnetic activity and starspot coverage fractions >50 percent, although a uniformly high spot coverage does not match the CMD well across the full luminosity range considered.

Automated summary

Astrometry and photometry data from Gaia, combined with spectroscopic data from the Gaia-ESO Survey, were used to identify the lithium depletion boundary in the young cluster NGC 2232. By comparing the location of the LDB in absolute color-magnitude diagrams with standard models, an age of 38 +/- 3 Myr was inferred. Models incorporating high levels of magnetic activity and starspot coverage fractions >50 percent showed the best agreement between LDB and CMD ages, particularly at ages of 45-50 Myr.