It is proved in this paper that the maximum number of limit cycles of system
⎧ dx/dt = y
⎨
⎩ dy/dt = kx - (k + 1)x2 + x3 + ε(α + βx + γx2)y
is equal to two in the finite plane, where k > (11 + √33) / 4 , 0 < |ε| << 1, |α| + |β| + |γ| ≠ 0. This is partial answer to the seventh question in [2], posed by Arnold.
@article{urn:eudml:doc:41390, title = {Bifurcations of limit cycles from cubic Hamiltonian systems with a center and a homoclinic saddle-loop.}, journal = {Publicacions Matem\`atiques}, volume = {44}, year = {2000}, pages = {205-235}, mrnumber = {MR1775762}, zbl = {0962.34026}, language = {en}, url = {http://dml.mathdoc.fr/item/urn:eudml:doc:41390} }
Zhao, Yulin; Zhang, Zhifen. Bifurcations of limit cycles from cubic Hamiltonian systems with a center and a homoclinic saddle-loop.. Publicacions Matemàtiques, Tome 44 (2000) pp. 205-235. http://gdmltest.u-ga.fr/item/urn:eudml:doc:41390/