LITHIUM IN OLD BINARY STARS

Through a detailed analysis of high resolution, high signal to noise s pectra, the lithium abundance of sixteen metal deficient binaries (-2. 9 less than or equal to [Fe/H] less than or equal to -0.4) with period s ranging from 220d to 1.8d has been measured. All these stars were su pposed to be dwarfs. A careful determination of the atmospheric parame ters revealed that some of them were slightly evolved. However all the stars here studied (but one: HD 89499) are in the interval 4900 great er than or equal to T-eff less than or equal to 6200K, log g greater t han or equal to 3. The stars are divided in two groups: old disk stars (-1.1 less than or equal to [Fe/H] less than or equal to -0.4) and ha lo stars ([Fe/H] less than or equal to -1.4). The present analysis whi ch includes for most of the stars a careful determination of the stell ar physical parameters (T-eff, log g, and [Fe/H]) shows that for T-eff greater than or equal to about 5000K the lithium abundance in long an d short period binaries does not differ from that of single dwarfs in the same interval of temperature, gravity and metallicity. When T-eff is less than or equal to about 5100K the lithium abundance is larger i n the short period binaries (which often have larger values of v sini) . Due to the very small number of metal deficient short period binarie s, the limit in temperature is rather uncertain and moreover it may de pend on the metallicity of the stars.These results, if confirmed by a larger sample would cast some doubts on theories predicting a strong L i depletion in old warm stars (and in particular in Pop II dwarfs) ind uced by strong angular momentum losses.