A revised age greater than 50 Myr for the young cluster IC 4665

IC 4665 is one of only a dozen young open clusters with a 'lithium depletion boundary' (LDB) age. Using an astrometrically and spectroscopically filtered sample of cluster members, we show that both the positions of its low-mass stars in Gaia absolute colour-magnitude diagrams and the lithium depletion seen among its K- and early M-stars are discordant with the reported LDB age of 32(-5)(+4) Myr. Re-analysis of archival spectra suggests that the LDB of IC 4665 has not been detected and that the published LDB age should be interpreted as a lower limit. Empirical comparisons with similar data sets from other young clusters with better-established LDB ages indicate that IC 4665 is bracketed in age by the clusters IC 2602 and IC 2391 at 55 +/- 3 Myr.

Automated summary

Through astrometric and spectroscopic analysis of IC 4665 members, it was found that the positions of low-mass stars and the lithium depletion among K and early M stars in the cluster do not match the reported LDB age. Re-analysis of the data suggests that the LDB of IC 4665 has not been detected and the reported LDB age should be interpreted as a lower limit. A comparison with other young clusters with better-established LDB ages indicates that IC 4665 has an age range of 55 +/- 3 Myr, bracketed by clusters IC 2602 and IC 2391.