Unitary forms for holomorphic vertex operator algebras of central charge 24

We prove that all holomorphic vertex operator algebras of central charge $24$ with non-trivial weight one subspaces are unitary. The main method is to use the orbifold construction a VOA $V$ directly from Niemeier lattice $V_N$. show it possible extend unitary form for $V_N$ by using and some information automorphism group $\mathrm{Aut}(V)$.