  We study a heavy-heavy-light three-body system confined to one space
dimension provided the binding energy of an excited state in the heavy-light
subsystems approaches zero. The associated two-body system is characterized by
(i) the structure of the weakly-bound excited heavy-light state and (ii) the
presence of deeply-bound heavy-light states. The consequences of these aspects
for the behavior of the three-body system are analyzed. We find strong
indication for universal behavior of both three-body binding energies and wave
functions for different weakly-bound excited states in the heavy-light
subsystems.
