Limit points for descent spectrum of operator matrices

In this paper, we investigate the limit points set of descent spectrum of upper triangular operator matrices MC=(AC0B) {M_C} = \left( {\matrix{A \hfill & C \hfill \cr 0 \hfill & B \hfill \cr } } \right) . We prove that acc(σ_des(M_C)) ∪ W_accσdes = acc(σ_des(A)) ∪ acc(σ_des(B)) where W_accσdes is the union of certain holes in acc(σ_des(M_C)), which happen to be subsets of acc(σ_asc(B)) ∩ acc(σ_des(A)). Furthermore, several sufficient conditions for acc(σ_des(M_C)) = acc(σ_des(A)) ∪ acc(σ_des(B)) holds for every C ∈ ℬ(Y, X) are given.