  We consider the 1-parameter family of planar quintic systems, $\dot x=
y^3-x^3$, $\dot y= -x+my^5$, introduced by A. Bacciotti in 1985. It is known
that it has at most one limit cycle and that it can exist only when the
parameter $m$ is in $(0.36,0.6)$. In this paper, using the Bendixon-Dulac
theorem, we give a new unified proof of all the previous results, we shrink
this to $(0.547,0.6)$, and we prove the hyperbolicity of the limit cycle. We
also consider the question of the existence of polycycles. The main interest
and difficulty for studying this family is that it is not a semi-complete
family of rotated vector fields. When the system has a limit cycle, we also
determine explicit lower bounds of the basin of attraction of the origin.
Finally we answer an open question about the change of stability of the origin
for an extension of the above systems.
