Stellar feedback efficiencies: supernovae versus stellar winds
  Stellar winds and supernova (SN) explosions of massive stars ("stellar
feedback") create bubbles in the interstellar medium (ISM) and insert newly
produced heavy elements and kinetic energy into their surroundings, possibly
driving turbulence. Most of this energy is thermalized and immediately removed
from the ISM by radiative cooling. The rest is available for driving ISM
dynamics. In this work we estimate the amount of feedback energy retained as
kinetic energy when the bubble walls have decelerated to the sound speed of the
ambient medium. We show that the feedback of the most massive star outweighs
the feedback from less massive stars. For a giant molecular cloud (GMC) mass of
1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation
efficiency of 8% the initial mass function predicts a most massive star of
approximately 60 solar masses. For this stellar evolution model we test the
dependence of the retained kinetic energy of the cold GMC gas on the inclusion
of stellar winds. In our model winds insert 2.34 times the energy of a SN and
create stellar wind bubbles serving as pressure reservoirs. We find that during
the pressure driven phases of the bubble evolution radiative losses peak near
the contact discontinuity (CD), and thus, the retained energy depends
critically on the scales of the mixing processes across the CD. Taking into
account the winds of massive stars increases the amount of kinetic energy
deposited in the cold ISM from 0.1% to a few percent of the feedback energy.
