LITHIUM ABUNDANCES IN NEARBY FGK DWARF AND SUBGIANT STARS: INTERNAL DESTRUCTION, GALACTIC CHEMICAL EVOLUTION, AND EXOPLANETS

We derive atmospheric parameters and lithium abundances for 671 stars and include our measurements in a literature compilation of 1381 dwarf and subgiant stars. First, a lithium desert in the effective temperature (T-eff) versus lithium abundance (A(Li)) plane is observed such that no stars with T-eff similar or equal to 6075 K and A(Li) similar or equal to 1.8 are found. We speculate that most of the stars on the low ALi side of the desert have experienced a short-lived period of severe surface lithium destruction as main-sequence or subgiant stars. Next, we search for differences in the lithium content of thin-disk and thick-disk stars, but we find that internal processes have erased from the stellar photospheres their possibly different histories of lithium enrichment. Nevertheless, we note that the maximum lithium abundance of thick-disk stars is nearly constant from [Fe/H] = -1.0 to -0.1, at a value that is similar to that measured in very metal-poor halo stars (A(Li) similar or equal to 2.2). Finally, differences in the lithium abundance distribution of known planet-host stars relative to otherwise ordinary stars appear when restricting the samples to narrow ranges of T-eff or mass, but they are fully explained by age and metallicity biases. We confirm the lack of a connection between low lithium abundance and planets. However, we find that no low A(Li) planet-hosts are found in the desert T-eff window. Provided that subtle sample biases are not responsible for this observation, this suggests that the presence of gas giant planets inhibit the mechanism responsible for the lithium desert.