Liouvillian and analytic integrability of the quadratic vector fields having an invariant ellipse

We characterize the Liouvillian and analytic integrability of the quadratic polynomial vector fields in .2 having an invariant ellipse. More precisely, a quadratic system having an invariant ellipse can be written into the form x.=x2+y2.1+y(ax+by+c), y.=.x(ax+by+c), and the ellipse becomes x 2 + y 2 = 1. We prove that (i) this quadratic system is analytic integrable if and only if a = 0 (ii) if x 2+y 2 = 1 is a periodic orbit, then this quadratic system is Liouvillian integrable if and only if x 2 + y 2 = 1 is not a limit cycle; and (iii) if x2 +y 2 = 1 is not a periodic orbit, then this quadratic system is Liouvilian integrable if and only if a = 0.