We have obtained high resolution spectra of 14 cool stars (G0-M1) in the open IC 4665 cluster. Excess H emission and Li abundances have been derived from the data. We find a large spread in both parameters. The dependence of H and Li with in IC 4665 seems similar to that in the Pleiades. Two IC 4665 stars (P146 and P166) with lower H emission and Li abundance than Pleiades stars of the same are suspected of not being cluster members, although their radial velocities do indicate membership. The Li abundances of IC 4665 stars support previous conclusions on PMS Li burning (Martín et al. 1994; García López et al. 1994): solar type stars experience little PMS Li depletion; late-G and early-K stars present a large spread of Li abundances (about 1 dex), which is related to activity and rotation in the sense that fast rotators have higher Li abundance and chromospheric emission; late-K and early-M stars experience very efficient Li depletion, which is larger than a factor of 100 for 4000 K.
The distribution of Li abundances in the low-mass stars of several open clusters (IC 2391, IC 4665, Per, Pleiades), and in post T Tauri stars, are rather similar. There can be two reasons for that: (a) the stars in different clusters and the PTTS span the same range of ages, and (b) Li and H are not precise age indicators between 20 and 100 Myr. We argue that relative ages of young clusters may be obtained in the near future using the "LL-clock". This would certainly help to clarify the evolution of Li and chromospheric activity during late PMS evolution.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998