Singularities of 3d vector fields preserving the form of Martinet

We study the local structure of vector fields on ${\mathbb{R}}^3$ which preserve the Martinet $1$-form $\alpha =(1+x)dy\pm zdz$. We present the classification of their singularities, up to diffeomorphisms preserving the form $\alpha$, as well as their transversal unfoldings. We are thus able to provide a fairly complete list of the bifurcations such vector fields undergo.