Parameter-ellipticity with respect to a closed subsector of the complex plane
for pseudodifferential Douglis-Nirenberg systems is discussed and shown to
imply the existence of a bounded H_\infty-calculus in suitable scales of
Sobolev, Besov, and Hoelder spaces. We also admit non pseudodifferential
perturbations. Applications concern systems with coefficients of mild Hoelder
regularity and the generalized thermoelastic plate equations.Comment: 22 page
