Lithium depletion and the rotational history of exoplanet host stars
Résumé
Context: It has been reported that exoplanet host stars are lithium depleted compared to solar-type stars without detected massive planets. Aims: We investigate whether enhanced lithium depletion in exoplanet host stars may result from their rotational history. Methods: We have developed rotational evolution models for slow and fast solar-type rotators from the pre-main sequence (PMS) to the age of the Sun and compare them to the distribution of rotational periods observed for solar-type stars between 1 Myr and 5 Gyr. Results: We show that slow rotators develop a high degree of differential rotation between the radiative core and the convective envelope, while fast rotators evolve with little core-envelope decoupling. We suggest that strong differential rotation at the base of the convective envelope is responsible for enhanced lithium depletion in slow rotators. Conclusions: We conclude that lithium-depleted exoplanet host stars were slow rotators on the zero-age main sequence (ZAMS) and argue that slow rotation results from a long lasting star-disk interaction during the PMS. Altogether, this suggests that long-lived disks (≥5 Myr) may be a necessary condition for massive planet formation/migration.