# Pick marginal circles in phase plot of a non-linear dynamic system

Context: I'm studying non-linear dynamics with Mathematica.

Part of the problem: Given the following system: $\ddot{x} = x - x^3 - 0.2 \dot{x} + g(\sin(t) + \cos(2t))$, find two values of $g$ that correspond to two marginal circles. I'm not sure whether I translate it correctly. A marginal circle is a closed phase curve that the system tends to when $t\to\infty$.

Here is the code I'm using:

deq = x''[t] == x[t] - x[t]^3 - 0.2 x'[t] + g (Sin[t] + Cos[2 t]);

drawOrbit[deq_, label_] :=
Module[{tmin = 100, tmax = 1000},
sol =
NDSolve[
{deq}, {x, x'}, {t, 0, tmax},
AccuracyGoal -> 10, PrecisionGoal -> 10,
MaxSteps -> \[Infinity]];
ParametricPlot[
{x[t], x'[t]} /. sol, {t, tmin, tmax},
AxesLabel -> {"x[t]", "x'[t]"},
PlotLabel -> label, PlotRange -> All, PlotPoints -> 1000]]

Grid@Partition[#, 3] &@
ParallelTable[
drawOrbit[{deq /. g -> k, x[0] == 0, x'[0] == 0},
"g=" <> ToString@k],
{k, 0.1, 1, 0.1}]


And this is the produced image:

My question is: Do I just pick two closed phase curves and calculate their orbits or is there more here I am missing ? Also, I suppose that I skip the strange attractors and the marginal circles that have >1 period like the one for $g=0.7$.

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