10. Given that the hyperbola $\frac { x ^ { 2 } } { a ^ { 2 } } - y ^ { 2 } = 1 ( a > 0 )$ has an asymptote $\sqrt { 3 } x + y = 0$, then $a =$ $\_\_\_\_$.
10. Given that the hyperbola $\frac { x ^ { 2 } } { a ^ { 2 } } - y ^ { 2 } = 1 ( a > 0 )$ has an asymptote $\sqrt { 3 } x + y = 0$, then $a =$ $\_\_\_\_$.\\