第一千一百零六章风尘吹泡泡
Dusty Wind-Blown Bubbles
摘要：
受最近对风吹气泡内24微米排放的观察的启发，我们研究了灰尘在这种环境中可以发挥的作用，并建立了一个特定的风吹气泡N49的近似模型。“首先，我们用一个充满灰尘的风吹气泡来模拟观测结果，然后询问尘埃是否可以在N49内存活到现在的年龄（估计为5x10^5到10^6年）。我们发现，尘埃溅射，特别是尘埃-气体摩擦，意味着尘埃在气泡的风冲击区域的生存时间相对较短（t ~ 10^4年）。为了解释24微米的排放，我们假设颗粒在风吹的气泡中通过破坏嵌入的、密集的ISM气体云而得到补充，ISM气体云已经被不断膨胀的风吹的气泡所淹没。我们计算了N49内的小云团的消融时间尺度，并找到了可以补充尘埃的嵌入式小云团的近似参数;小云团的参数与在其他星云中观察到的参数大致相似。这样的尘埃将对气泡产生重要的影响：在N49的风吹气泡模型中，包括简单的尘埃冷却，我们发现在大约10^4年的气泡年龄时，亮度大约高出6倍。在年龄为10^7年时，如果将尘埃包括在内，气泡中所含的能量将降低约8倍;如果必须在气泡内补充尘埃，则相关的伴随气体质量对于风吹气泡的冷却和演化也非常重要。虽然当然需要更详细的模型，但这项工作说明了灰尘在风吹气泡中可能具有的重要性，并且是迈向灰尘，风吹气泡模型的第一步。
英文摘要：
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.
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