  Superbubbles surrounding OB associations provide ideal laboratories to study
the stellar energy feedback problem because the stellar energy input can be
estimated from the observed stellar content of the OB associations and the
interstellar thermal and kinetic energies of superbubbles are well-defined and
easy to observe. We have used DEM L 192, also known as N 51D, to carry out a
detailed case study of the energy budget in a superbubble, and we find that the
expected amount of stellar mechanical energy injected into the ISM,
(18+-5)x10^51 ergs, exceeds the amount of thermal and kinetic energies stored
in the superbubble, (6+-2)x10^51 ergs. Clearly, a significant fraction of the
stellar mechanical energy must have been converted to other forms of energy.
The X-ray spectrum of the diffuse emission from DEM L 192 requires a power-law
component to explain the featureless emission at 1.0-3.0 keV. The origin of
this power-law component is unclear, but it may be responsible for the
discrepancy between the stellar energy input and the observed interstellar
energy in DEM L 192.
