stability in the periodic orbit and in the singular point

$\dot{x}=-y+\lambda x(36-9{x}^{2}-{y}^{2})\phantom{\rule{0ex}{0ex}}\dot{y}=9x+\lambda y(36-9{x}^{2}-{y}^{2})\phantom{\rule{0ex}{0ex}}\dot{z}=-6z-{\lambda}^{2}{x}^{2}{y}^{2}{z}^{3}$

I want to analyze the stability in the periodic orbit and in the singular point, so for the singular point I take the derived matrix of the linear part, and I got the eigenvalues, wich are ${\lambda}_{1}=-6$, ${\lambda}_{2}=3i$ , $\lambda =-3i$ . I wanted to use Andronov-Vitt but I have two eigenvalues with no real part so I can´t, does anybody can help me with this?

$\dot{x}=-y+\lambda x(36-9{x}^{2}-{y}^{2})\phantom{\rule{0ex}{0ex}}\dot{y}=9x+\lambda y(36-9{x}^{2}-{y}^{2})\phantom{\rule{0ex}{0ex}}\dot{z}=-6z-{\lambda}^{2}{x}^{2}{y}^{2}{z}^{3}$

I want to analyze the stability in the periodic orbit and in the singular point, so for the singular point I take the derived matrix of the linear part, and I got the eigenvalues, wich are ${\lambda}_{1}=-6$, ${\lambda}_{2}=3i$ , $\lambda =-3i$ . I wanted to use Andronov-Vitt but I have two eigenvalues with no real part so I can´t, does anybody can help me with this?