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

TL;DR

This study revises the age of the young cluster IC 4665 to be greater than 50 million years, challenging previous estimates based on lithium depletion boundary methods.

Contribution

The paper provides a re-evaluation of IC 4665's age using Gaia data and archival spectra, suggesting it is older than previously thought and refining its age estimate.

Findings

IC 4665's low-mass stars' positions conflict with the earlier LDB age.

The LDB of IC 4665 was not definitively detected in archival spectra.

IC 4665's age is estimated to be around 55 Myr, older than prior estimates.

Abstract

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 +4/-5) 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 datasets 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.