Parametric Curve(s)

$$$ \forall\alpha\in\{0,2\pi\}\quad\; k_{a}\in \mathbb{R}\quad0.05\leqslant\;k_{a}\;\leqslant0.16$$$
$$$ \left \{ \begin{array}{r c l} \theta(\alpha)& = &\alpha \\ r(\alpha)& = &k_{a}\times\left(\cos^2{(2.5\cdot\alpha)}-1.5\right) \end{array}\right .$$$