H emission fluxes and lithium abundances of low-mass stars in the young open cluster IC 4665 *
E.L. Martín 1 and
D. Montes 2
Received 30 January 1996 / Accepted 15 May 1996
As part of a long term effort to understand pre-main sequence Li burning, we have obtained high resolution spectroscopic observations of 14 late type stars (G0-M1) in the young open cluster IC 4665. Most of the stars have H filled-in and Li I absorption, as expected for their young age. >From the equivalent widths of H emission excess (obtained using the spectral subtraction technique) and the Li I 6708 feature, we have derived H emission fluxes and photospheric Li abundances. The mean Li abundance of IC 4665 solar-type stars is log N(Li)=3.1; the same as in other young clusters ( Per, Pleiades) and T Tauri stars. Our results support the conclusions from previous works that PMS Li depletion is very small for masses 1 . Among the IC 4665 late-G and early K-type stars, there is a spread in Li abundances of about one order of magnitude. The Li-poor IC 4665 members have low H excess and vsini 10. Hence, the Li-activity-rotation connection which has been clearly established in the Pleiades also seems to hold in IC 4665. One M-type IC 4665 star that we have observed does not show Li, implying a very efficient Li depletion as observed in Per stars of the same spectral type.
The level of chromospheric activity and Li depletion among the low-mass stars of IC 4665 is similar to that in the Pleiades. In fact, we note that the Li abundance distributions in several young clusters ( Per, Pleiades, IC 2391, IC 4665) and in post T Tauri stars are strikingly similar. This result suggests that H emission and Li abundance not well correlated with age for low-mass stars between 20 and 100 Myr old. We argue that a finer age indicator, the "LL-clock", would be the luminosity at which the transition between efficient Li depletion and preservation takes place for fully convective objects. The LL-clock could allow in the near future to derive the relative ages of young open clusters, and clarify the study of PMS evolution of cool stars.
Key words: stars: abundances, activity, pre-main sequence clusters: open: IC 4665
* Based on observations made with the Isaac Newton telescope, operated on the island of La Palma by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, and with the 3.5 m telescope of the German-Spanish Calar Alto Observatory.
Send offprint requests to: E.L. Martín, (email@example.com)
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998