Impact of rotation and disc lifetime on pre-main sequence lithium depletion of solar-type stars

Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Suisse
e-mail: patrick.eggenberger@unige.ch; lionel.haemmerle@unige.ch; georges.meynet@unige.ch; andre.maeder@unige.ch;

Received: 10 November 2011
Accepted: 4 January 2012

Abstract

Aims. We study the influence of rotation and disc lifetime on lithium depletion of pre-main sequence (PMS) solar-type stars.

Methods. The impact of rotational mixing and of the hydrostatic effects of rotation on lithium abundances are investigated by computing non-rotating and rotating PMS models that include a comprehensive treatment of shellular rotation. The influence of the disc lifetime is then studied by comparing the lithium content of PMS rotating models experiencing different durations of the disc-locking phase between 3 and 9 Myr.

Results. The surface lithium abundance at the end of the PMS is decreased when rotational effects are included. During the beginning of the lithium depletion phase, only hydrostatic effects of rotation are at work. This results in a decrease in the lithium depletion rate for rotating models compared to non-rotating ones. When the convective envelope recedes from the stellar centre, rotational mixing begins to play an important role due to differential rotation near the bottom of the convective envelope. This mixing results in a decrease in the surface lithium abundance with a limited contribution from hydrostatic effects of rotation, which favours lithium depletion during the second part of the PMS evolution. The impact of rotation on PMS lithium depletion is also found to be sensitive to the duration of the disc-locking phase. When the disc lifetime increases, the PMS lithium abundance of a solar-type star decreases owing to the higher efficiency of rotational mixing in the radiative zone. A relationship between the surface rotation and lithium abundance at the end of the PMS is then obtained: slow rotators on the zero-age main sequence are predicted to be more lithium-depleted than fast rotators due to the increase in the disc lifetime.