Li I AND K I SCATTER IN COOL PLEIADES DWARFS

We utilize high-resolution (R similar to 60,000), high signal-to-noise ratio (similar to 100) spectroscopy of 17 cool Pleiades dwarfs to examine the confounding star-to-star scatter in the lambda 6707 Li I line strengths in this young cluster. Our Pleiades, selected for their small projected rotational velocity and modest chromospheric emission, evince substantial scatter in the line strengths of lambda 6707 Li I feature that is absent in the lambda 7699 K I resonance line. The Li I scatter is not correlated with that in the high-excitation lambda 7774 O I feature, and the magnitude of the former is greater than the latter despite the larger temperature sensitivity of the O I feature. These results suggest that systematic errors in line strength measurements due to blending, color (or color-based T(eff)) errors, or line formation effects related to an overlying chromosphere are not the principal source of Li I scatter in our stars. There do exist analytic spot models that can produce, via line formation effects, the observed Li scatter without introducing scatter in the K I line strengths or the color-magnitude diagram. However, these models predict factor of >= 3 differences in abundances derived from the subordinate lambda 6104 and resonance lambda 6707 Li I features; we find no difference in the abundances determined from these two features. These analytic spot models also predict CN line strengths significantly larger than we observe in our spectra. The simplest explanation of the Li, K, CN, and photometric data is that there must be a real abundance component to the Pleiades Li dispersion. We suggest that this real abundance component is the manifestation of relic differences in erstwhile pre-main-sequence Li burning caused by effects of surface activity on stellar structure. We discuss observational predictions of these effects, which may be related to other anomalous stellar phenomena.