Small limit cycles bifurcating from fine focus points in quartic order Z3-equivariant vector fields

This paper is concerned with the number of limit cycles for a quartic polynomial Z3-equivariant vector fields. The system under consideration has a fine focus point at the origin, and three fine focus points which are symmetric about the origin. By the computation of the singular point values, sixteen limit cycles are found and their distributions are studied by using the new methods of bifurcation theory and qualitative analysis. This is a new result in the study of the second part of the 16th Hilbert problem. It gives rise to the conclusion: H(4)⩾16, where H(n) is the Hilbert number for the second part of Hilbert's 16th problem. The process of the proof is algebraic and symbolic. As far as know, the technique employed in this work is different from more usual ones, the calculation can be readily done with using computer symbol operation system such as Mathematica.