  Forward-backward asymmetries, $A_{FB}^Q$, are important observables for the
determination of the neutral-current couplings of heavy quarks in inclusive
heavy quark production, $e^+ e^- \to \gamma^*, Z^* \to Q +X$. In view of the
measurement perspectives on $A_{FB}^Q$ at a future linear collider, precise
predictions of $A_{FB}^Q$ are required for massive quarks. We compute the
contribution of the $Q \bar Q$ final state to $A_{FB}^Q$ to order $\as^2$ in
the QCD coupling. We provide general formulae, and we show that this
contribution to $A_{FB}^Q$ is infrared-finite. We evaluate these two-parton
contributions for $b$ and $c$ quarks on and near the $Z$ resonance, and for $t$
quarks above threshold. Moreover, near the $t \bar t$ threshold we obtain, by
expanding in the heavy-quark velocity $\beta$, an expression for $A_{FB}^{t
\bar t}$ to order $\as^2$ and NNLL in $\beta$. This quantity is equal, to this
order in $\beta$, to the complete forward-backward asymmetry $A_{FB}^t$.

High Energy Physics - Phenomenology