The Lithium-Rotation Correlation in the Pleiades Revisited

Abstract

The dispersion in lithium abundance at Ðxed e †ective 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 temperature trend, rather than the absolute abundances, should be used to analyze the spread in abundance. We present evidence that the dispersion in Li equivalent widths at Ðxed color in cool single Pleiades stars is at least partially caused by stellar atmosphere e †ects (most likely departures from ionization predictions of model photospheres) rather than being completely explained by genuine abundance di †erences. We Ðnd that e †ective temperature estimates from di †erent colors yield systematically di †erent values for active stars. There is also a strong correlation between stellar activity and Li excess, but not a one-to-one mapping between unprojected stellar rotation (from photometric periods) and Li excess. Thus, it is unlikely that rotation is the main cause for the dispersion in the Li abundances. Finally, there is a signiÐcant correlation between detrended Li excess and potassium excess but not calciumÈperhaps supporting incomplete radiative transfer calculations (and overionization e †ects in particular) as an important source of the Li scatter. Other mechanisms, such as very small metallicity variations and magnetic Ðelds, which inÑuence preÈmain-sequence Li burning may also play a role. Finally, we Ðnd no statistical evidence for a decrease in dispersion in the coolest Pleiades stars, contrary to some previous work.