  Relying only on first principles, we derive a master equation of Lindblad
form generally applicable for adiabatically time dependent systems. Our
analysis shows that the much debated secular approximation can be valid for
slowly time dependent Hamiltonians when performed in an appropriate basis. We
apply our approach to the well known Landau-Zener problem where we find that
adiabaticity is improved by coupling to a low temperature environment.
