Perturbations of spectra of operator matrices

In this article M-C denotes a 2 x 2 operator matrix of the form M-C = [(A)(0) (C)(B)], which is acting on the product of Banach or Hilbert spaces X + Y. We investigate sets boolean AND/Cis an element ofL(Y,X) sigma(tau) (M-C), where sigma(tau) (M-C) can be equal to the left (right), essential, left (right) Fredholm, Weyl or Browder spectrum of M-C. Thus, generalizations and extensions of various well-known and recent results of H. Du and J. Pan (Proc. Amer. Math. Soc. 121 (1994), 761-766), J.K. Han, H.Y. Lee and W.Y. Lee (Proc. Amer. Math. Soc. 128 (2000), 119-123) and W.Y. Lee (Proc. Amer. Math. Soc. 129 (2000), 131-138) are presented.