Lithium depletion and the rotational history of exoplanet host stars

TL;DR

This study links the lithium depletion in exoplanet host stars to their rotational history, suggesting that slow initial rotation caused by prolonged star-disk interaction leads to enhanced lithium depletion and possibly influences planet formation.

Contribution

The paper introduces rotational evolution models connecting lithium depletion in stars to their early rotational history and disk interactions, providing a new explanation for observed lithium differences in planet-hosting stars.

Findings

Slow rotators develop significant core-envelope differential rotation.

Differential rotation enhances lithium depletion in slow rotators.

Long-lasting star-disk interactions may be crucial for massive planet formation.

Abstract

Israelian et al. (2004) reported that exoplanet host stars are lithium depleted compared to solar-type stars without detected massive planets, a result recently confirmed by Gonzalez (2008). We investigate whether enhanced lithium depletion in exoplanet host stars may result from their rotational history. 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. 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. 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.