  I discuss the temperature dependence of quarkonium correlators calculated in
lattice QCD. I show that the dominant source of the temperature dependence
comes from the zero mode contribution, while the the temperature dependence
associated with melting of bound states is quite small. I study the zero mode
contribution quantitatively for different quark masses and show that it is well
described by a quasi-particle model with temperature dependent heavy quark
mass. As a byproduct an estimate of the medium dependence of the heavy quark
mass is obtained.
