The lithium abundance - Constraints on stellar evolution
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Abstract
Some arguments about the role of lithium abundances in constraining evolutionary processes in halo stars are discussed. Attention is given to the recent observations of Spite and Spite (1982) which showed that the lithium abundance in solar and halo and disk stars (between 5500 and 6200 K) is N(Li)/N(H) = 10 to the -10th. It is found that not a single value for the ratio (alpha) of the mixing length to pressure scale height indicates variations of the Li abundance by less than a factor of 10 in evolutionary models of various masses in the effective temperature range between 5500 and 6200 K. Even if alpha is allowed to vary from one evolutionary sequence to another the minimum Li reduction is by a factor of 4. For the Li abundance to be reduced by more than a factor of 2 during the evolution requires that alpha adjusted itself during evolution so that the temperature at the bottom of mixed (gravitational zone) remained between log 6.2 and log 6.4 of the effective temperature.