We developed angular momentum evolution models for 0.5 and 0.8 M⊙
stars. The parametric models include a new wind braking law based on recent
numerical simulations of magnetised stellar winds, specific dynamo and
mass-loss rate prescriptions, as well as core/envelope decoupling. We compare
model predictions to the distributions of rotational periods measured for low
mass stars belonging to star forming regions and young open clusters.
Furthermore, we explore the mass dependence of model parameters by comparing
these new models to the solar-mass models we developed earlier. Rotational
evolution models are computed for slow, median, and fast rotators at each
stellar mass. The models reproduce reasonably well the rotational behaviour of
low-mass stars between 1 Myr and 8-10 Gyr, including pre-main sequence to
zero-age main sequence spin up, prompt zero-age main sequence spin down, and
early-main sequence convergence of the surface rotation rates. Fast rotators
are found to have systematically shorter disk lifetimes than moderate and slow
rotators, thus enabling dramatic pre-main sequence spin up. They also have
shorter core-envelope coupling timescales, i.e., more uniform internal
rotation. As to the mass dependence, lower mass stars require significantly
longer core-envelope coupling timescale than solar-type ones, which results in
strong differential rotation developing in the stellar interior on the early
main sequence. Lower mass stars also require a weaker braking torque to account
for their longer spin down timescale on the early main sequence, while they
ultimately converge towards lower rotational velocities than solar-type stars
on the longer term due to their reduced moment of inertia. We also find
evidence that the mass-dependence of the wind braking efficiency may be related
to a change of the magnetic topology in lower mass stars.Comment: 17 pages, 11 figures, accepted for publication in A&
