设双曲线\(C\):\( \dfrac {x^{2}}{2}- \dfrac {y^{2}}{3}=1\),\(F_{1}\),\(F_{2}\)为其左右两个焦点.
\((1)\)设\(O\)为坐标原点,\(M\)为双曲线\(C\)右支上任意一点,求\( \overrightarrow{OM}\cdot \overrightarrow{F_{1}M}\)的取值范围;
\((2)\)若动点\(P\)与双曲线\(C\)的两个焦点\(F_{1}\),\(F_{2}\)的距离之和为定值,且\(\cos ∠F_{1}PF_{2}\)的最小值为\(- \dfrac {1}{9}\),求动点\(P\)的轨迹方程.