DUSTY WIND-BLOWN BUBBLES

Spurred by recent observations of 24 mu m emission within wind-blown bubbles (WBBs), we study the role that dust can play in such environments and build an approximate model of a particular WBB, N49. First, we model the observations with a dusty WBB, and then ask whether dust could survive within N49 to its present age (estimated to be 5 x 10(5) to 10(6) yr). We find that dust sputtering and especially dust-gas friction would imply relatively short timescales (t similar to 10(4) yr) for dust survival in the wind-shocked region of the bubble. To explain the 24 mu m emission, we postulate that the grains are replenished within the WBB by destruction of embedded, dense cloudlets of interstellar medium gas that have been overrun by the expanding WBB. 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 WBB model for N49, we find that the luminosity is higher by approximately a factor of 6 at a bubble age of about 10(4) yr. At ages of 10(7) yr, the energy contained in the bubble is lower by about a factor of 8 if dust is included; if dust must be replenished within the bubble, the associated accompanying gas mass will also be very important to WBB cooling and evolution. While more detailed models are certainly called for, this work illustrates the possible strong importance of dust in WBBs, and is a first step toward models of dusty WBBs.