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abstract
We have observed 11 low mass Pleiades members with the HIRES echelle spectrograph on the Keck 10-meter telescope. These observations extend the work of Soderblom et al (A.J. vol. 106, p. 1059, 1993) to lower masses. The stars ranged in effective temperature from 3900 $^\circ$K to 4580 $^\circ$K with five of the stars having temperatures below 4,000 $^\circ$K.
We have detected lithium in only one Pleiad with a temperature below 4,000 $^\circ$K (HII 1756, temperature 3,980 $^\circ)$K. This star is a slow rotator (vsin i = 6 km s$^{-1}$), and the lithium abundance was $\rm log\ N(Li)=0.5$. The other stars with temperatures below 4,000 $^\circ$K had rotational velocities up to 80 km s$^{-1}$ and upper limits on the lithium abundance ranging from log N(Li)=0.2 to -0.1.
We detected lithium in all stars with temperatures greater than 4,000 $^\circ$K except for HII 2927, the fastest rotator of the stars observed, with a vsin i of 96 km s$^{-1}$. We tentatively conclude that the large dispersion in lithium abundance seen between temperatures of 5,200 $^\circ$K and 4,500 $^\circ$K (masses between 0.95 and 0.72 $M_{\sun}$) has narrowed considerably at a temperature of 4,100 $^\circ$K (0.65$M_{\sun}$). Moreover, the correlation between rotation and lithium abundance seems to have weakened.
