ISSN : 1226-0657
In this paper, we study the dynamics of a two-parameter unfolding system <TEX>$\chi$</TEX>' = y, y' = <TEX>$\beta$</TEX>y+<TEX>$\alpha$</TEX>f(<TEX>$\chi\alpha\pm\chiy$</TEX>+yg(<TEX>$\chi$</TEX>), where f(<TEX>$\chi$</TEX>,<TEX>$\alpha$</TEX>) is a second order polynomial in <TEX>$\chi$</TEX> and g(<TEX>$\chi$</TEX>) is strictly nonlinear in <TEX>$\chi$</TEX>. We show that the higher order term yg(<TEX>$\chi$</TEX>) in the system does not change qulitative structure of the Hopf bifurcations near the fixed points for small <TEX>$\alpha$</TEX> and <TEX>$\beta$</TEX> if the nontrivial fixed point approaches to the origin as <TEX>$\alpha$</TEX> approaches zero.