  Quarkonium properties at finite temperature have been studied with quark
masses of the charm and bottom quarks. Our simulations have been performed in
quenched QCD with the $O(a)$-improved Wilson quarks on large and fine isotropic
lattices with the spatial lattice extents $N_\sigma =$ 96, 192 and the
corresponding lattice spacings $a =$ 0.0190, 0.00967 fm, respectively, at
temperatures in a range between about 0.7$T_c$ and 1.4$T_c$. We show
temperature and quark mass dependence of quarkonium correlation functions and
related physical quantities: the quark number susceptibility and the heavy
quark diffusion constant.
