THE LITHIUM CONTENT AND OTHER PROPERTIES OF F2-G5 GIANTS IN THE HERTZSPRUNG GAP

As stars of 2-5M. evolve across the Hertzsprung Gap they should first deplete their surface lithium by convective dilution and then, when co nvection penetrates deeper, begin to bring CN processed material to th eir surfaces. To investigate this process we have observed 52 giants, 25 of which have known C/N ratios, for their Li abundances. After elim inating four stars that may actually be dwarfs and including the two c omponents of Capella analyzed by Pilachowski and Sowell we have compar ed our [Li/Fe] ratios with models of Swenson. For stars showing upsilo n sin i>50 km s-1 we find [Li/Fe] to be uneffected by mixing for B - V <0.7 as predicted. For stars cooler than B - V=0.7 both upsilon sin i and [Li/Fe] drop to smaller values. For the sharp lined stars (upsilon sin i<50 km s-1) we find a drop in Li between B - V=0.45 and 0.60 whi ch cannot be understood in terms of dilution by convection. Various po ssible causes of such an early depletion or dilution of surface Li are discussed including diffusion at the base of the convection zone, mas s loss possibly enhanced by pulsation, and magnetic activity as in the magnetic A and B type stars. The models of Richer & Michaud [ApJ, 416 , 312 (1993)] with diffusion point toward a satisfactory solution. A f ew giants with low upsilon sin i values stand out with much higher tha n expected [Li/Fe] values despite their cool effective temperatures. W e do not understand why those stars have not depleted their lithium as have most giants of similar color. The correlation of [N/C] with [Li/ Fe] follows expectations in so far as almost all stars with enhanced [ N/C] have depleted their Li as well.