  A closed expression for the density operator of the damped harmonic
oscillator is extracted from the master equation based on the Lindblad theory
for open quantum systems. The entropy and effective temperature of the system
are subsequently calculated and their temporal behaviour is surveyed by showing
how these quantities relax to their equilibrium values. The entropy for a state
characterized by a Wigner distribution function which is Gaussian in form is
found to depend only on the variance of the distribution function.
