Erratum: Eq. (28) should have opposite sign, i.e. $e_{0Q}=-\cos (\vec{v_0},\vec{r_Q})=- \cos (\theta _0)\cos (\phi _0-\phi)$. However, numbers and orientation of the warp are correct as stated.
Author comment submitted on 26 May, 2011 by Martín López-Corredoira ( martinlc@iac.es )