已知椭圆\(C_{1}\):\( \dfrac {x^{2}}{a^{2}}+y^{2}=1(a > 1)\)的离心率\(e= \dfrac { \sqrt {2}}{2}\),左、右焦点分别为\(F_{1}\)、\(F_{2}\),直线\(l_{1}\)过点\(F_{1}\)且垂直于椭圆的长轴,动直线\(l_{2}\)垂直\(l_{1}\)于点\(P\),线段\(PF_{2}\)的垂直平分线交\(l_{2}\)于点\(M\).
\((1)\)求点\(M\)的轨迹\(C_{2}\)的方程;
\((2)\)当直线\(AB\)与椭圆\(C_{1}\)相切,交\(C_{2}\)于点\(A\),\(B\),当\(∠AOB=90^{\circ}\)时,求\(AB\)的直线方程.