  Two noncentrosymmetric ternary pnictides, CaAgP and CaAgAs, are reported as
topological line-node semimetals protected solely by mirror-reflection
symmetry. The band gap vanishes on a circle in momentum space, and surface
states emerge within the circle. Extending this study to spin-orbit coupled
systems reveals that, compared with CaAgP, a substantial band gap is induced in
CaAgAs by large spin-orbit interaction. The resulting states are a topological
insulator, in which the Z2 topological invariant is given by 1; 000. To clarify
the Z2 topological invariants for time-reversal-invariant systems without
spatial-inversion symmetry, we introduce an alternative way to calculate the
invariants characterizing a line node and topological insulator for
mirror-reflection-invariant systems.
