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A Comparative Study on Lithium Abundances in Solar--Type Stars With and Without Planets

We have investigated the abundance anomalies of lithium for stars with planets in the temperature range of 5600--5900 K reported by Israelian and coworkers, as compared to 20 normal stars at the same temperature and metallicity ranges. Our result indicates a higher probability of lithium depletion for stars with planets in the main--sequence stage. It seems that stellar photospheric abundances of lithium in stars with planets may be somewhat affected by the presence of planets. Two possible mechanisms are considered to account for the lower Li abundances of stars with planets. One is related to the rotation-induced mixing due to the conservation of angular momentum by the protoplanetary disk, and the other is a shear instability triggered by planet migration. These results provide new information on stellar evolution and the lithium evolution of the Galaxy.