Dusty Wind-Blown Bubbles
  Spurred by recent observations of 24 micron emission within wind-blown
bubbles, we study the role that dust can play in such environments, and build
an approximate model of a particular wind-blown bubble, `N49.' First, we model
the observations with a dusty wind-blown bubble, and then ask whether dust
could survive within N49 to its present age (estimated to be 5x10^5 to 10^6
years). We find that dust sputtering and especially dust-gas friction would
imply relatively short timescales (t ~ 10^4 years) for dust survival in the
wind-shocked region of the bubble. To explain the 24 micron emission, we
postulate that the grains are replenished within the wind-blown bubble by
destruction of embedded, dense cloudlets of ISM gas that have been over-run by
the expanding wind-blown bubble. We calculate the ablation timescales for
cloudlets within N49 and find approximate parameters for the embedded cloudlets
that can replenish the dust; the parameters for the cloudlets are roughly
similar to those observed in other nebula. Such dust will have an important
effect on the bubble: including simple dust cooling in a wind-blown bubble
model for N49, we find that the luminosity is higher by approximately a factor
of six at a bubble age of about 10^4 years. At ages of 10^7 years, the energy
contained in the bubble is lower by about a factor of eight if dust is
included; if dust must be replenished within the bubble, the associated
accompanying gas mass will also be very important to wind-blown bubble cooling
and evolution. While more detailed models are certainly called for, this work
illustrates the possible strong importance of dust in wind-blown bubbles, and
is a first step toward models of dusty, wind-blown bubbles.
