The lithium-rotation correlation in the Pleiades revisited

The dispersion in lithium abundance at fixed effective temperature in young cool stars like the Pleiades has proved a difficult challenge for stellar evolution theory. We propose that Li abundances relative to a mean temperat ure trend, rather than the absolute abundances, should be used to analyze t he spread in abundance. We present evidence that the dispersion in Li equiv alent widths at fixed color in cool single Pleiades stars is at least parti ally caused by stellar atmosphere effects (most likely departures from ioni zation predictions of model photospheres) rather than being completely expl ained by genuine abundance differences. We find that effective temperature estimates from different colors yield systematically different values for a ctive stars. There is also a strong correlation between stellar activity an d Li excess, but not a one-to-one mapping between unprojected stellar rotat ion (from photometric periods) and Li excess. Thus, it is unlikely that rot ation is the main cause for the dispersion in the Li abundances. Finally, t here is a significant correlation between detrended Li excess and potassium excess but not calcium-perhaps supporting incomplete radiative transfer ca lculations (and overionization effects in particular) as an important sourc e of the Li scatter. Other mechanisms, such as very small metallicity varia tions and magnetic fields, which influence pre-main-sequence Li burning may also play a role. Finally, we find no statistical evidence for a decrease in dispersion in the coolest Pleiades stars, contrary to some previous work .