  The temperature dependence of the mass, leptonic decay constant, and width of
heavy-light quark peseudoscalar and vector mesons is obtained in the framework
of thermal Hilbert moment QCD sum rules. The leptonic decay constants of both
pseudoscalar and vector mesons decrease with increasing $T$, and vanish at a
critical temperature $T_c$, while the mesons develop a width which increases
dramatically and diverges at $T_c$, where $T_c$ is the temperature for
chiral-symmetry restoration. These results indicate the disappearance of
hadrons from the spectral function, which then becomes a smooth function of the
energy. This is interpreted as a signal for deconfinement at $T=T_c$. In
contrast, the masses show little dependence on the temperature, except very
close to $T_c$, where the pseudoscalar meson mass increases slightly by 10-20
%, and the vector meson mass decreases by some 20-30 %
