  We study several fundamental operators in harmonic analysis related to Bessel
operators, including maximal operators related to heat and Poisson semigroups,
Littlewood-Paley-Stein square functions, multipliers of Laplace transform type
and Riesz transforms. We show that these are (vector-valued) Calder\'on-Zygmund
operators in the sense of the associated space of homogeneous type, and hence
their mapping properties follow from the general theory.
