The dynamics of maps tangent to the identity and with non-vanishing index

Let f be a germ of holomorphic self-map of C^2 at the origin O tangent to the identity, and with O as a non-dicritical isolated fixed point. A parabolic curve for f is a holomorphic f-invariant curve, with O on the boundary, attracted by O under the action of f. It has been shown that if the characteristic direction [v] has residual index not belonging to Q^+, then there exist parabolic curves for f tangent to [v]. In this paper we prove, with a different method, that the conclusion still holds just assuming that the residual index is not vanishing (at least when f is regular along [v]).