Union curves in W2 relative to a congruence and union curvature of a curve in W2

In this paper, firstly we obtained differential equation of the union curves in $W_2$. Then, we showed that obtained equation is equivalent to apair of differential equations of the second order. We denoted it by $(eta_1,eta_2)$ and we named $eta_1$ and $eta_2$ as the components of the union curvature vector field.We defined union curves in $W_2$ relative a congruence by means of the union curvature vector field. Finally, we expressed union curvature of a curve in $W_2$ in terms of the components of the union curvature vector field.