Пространства орбит торических действий на многообразиях Хессенберга
We consider effective actions of a compact torus Tn−1 on an even-dimensional smooth manifold M2n with isolated fixed points. We prove that under certain conditions on weights of tangent representations, the orbit space is a manifold with corners. Given that the action is Hamiltonian, the orbit space is homeomorphic to Sn+1∖(U1⊔…⊔Ul) where Sn+1 is the (n+1)--sphere and U1,…,Ul are open domains. We apply the results to regular Hessenberg varieties and manifolds of isospectral Hermitian matrices of staircase form.