Bulk viscosity in a hyperonic star and r-mode instability

We consider a rotating neutron star with the presence of hyperons in its core. We use an equation of state in an effective chiral model within the relativistic mean-field approximation. We calculate the hyperonic bulk viscosity coefficient caused by nonleptonic weak interactions. By estimating the damping time scales of the dissipative processes, we investigate its role in the suppression of gravitationally driven instabilities in the r mode. We observe that r-mode instability remains very significant for hyperon core temperatures of around 10(8) K, which results in a comparatively larger instability window. We find that such instability can reduce the angular velocity of the rapidly rotating star considerably up to similar to 0.04 Omega(K), with Omega(K) as the Keplerian angular velocity.