On the limit cycles bifurcating from an ellipse of a quadratic center

Consider the class of all quadratic centers whose period annulus has a periodic solution whose phase curve is an ellipse E. The period annulus of any of such quadratic centers has cyclicity at least one, and this one is due to a family of algebraic limit cycles(formed by ellipses) bifurcating from the ellipse E. quadratic systems, quadratic vector fields, quadratic center, periodic orbit, limit cycle, bifurcation from center, cyclicity of the period annulus, inverse integrating factor