Lithium abundances from the 6104A line in cool Pleiades stars

Lithium abundances determined by spectral synthesis from both the 6708A resonance line and the 6104 subordinate line are reported for 11 late-type Pleiades stars, including spectra previously analysed by Russell (1996). We report a 0.7 dex scatter in the abundances from 6708A, and a scatter at least as large from the 6104A line. We find a reasonable correllation between the 6104A and 6708A Li abundances, although four stars have 6104A-determined abundances which are significantly larger than the 6708-determined values, by up to 0.5 dex, suggesting problems with the homogeneous, one-dimensional atmospheres being used. We show that these discrepancies can be explained, although probably not uniquely, by the presence of star spots with plausible coverage fractions. The addition of spots does not significantly reduce the apparent scatter in Li abundances, leaving open the possibility that at least some of the spread is caused by real star-to-star differences in pre-main- sequence Li depletion.Comment: 13 pages, 7 figures; Accepted by A&A 17/05/0

The Keele-Exeter young cluster survey - I. Low-mass pre-main-sequence stars in NGC 2169

We have used RCIC CCD photometry from the Isaac Newton telescope and intermediate-resolution spectroscopy from the Gemini North telescope to identify and characterize low-mass (0.15 < M/M⊙ < 1.3) pre-main-sequence stars in the young open cluster NGC 2169. Isochrone fitting to the high- and low-mass populations yields an intrinsic distance modulus of 10.13+0.06−0.09 mag and a model-dependent age of 9 ± 2 Myr. Compared to the nearby, kinematically defined groups of a similar age, NGC 2169 has a large low-mass population which potentially offers a more precise statistical investigation of several aspects of star formation and early stellar evolution. By modelling the distribution of low-mass stars in the IC versus RC−IC diagram, we find that any age spread among cluster members has a Gaussian full width at half-maximum (FWHM) ≤ 2.5 Myr. A young age and a small age spread (<10 Myr) are supported by the lack of significant lithium depletion in the vast majority of cluster members. There is no clear evidence for accretion or warm circumstellar dust in the low-mass members of NGC 2169, bolstering the idea that strong accretion has ceased and inner discs have dispersed in almost all low-mass stars by ages of 10 Myr