星光和沙尘暴：AGB上的质量损失机制
Starlight and Sandstorms: Mass Loss Mechanisms on the AGB
摘要：
有强有力的观测迹象表明，冷发光AGB星的密集慢风是由尘埃颗粒上的辐射压力驱动的，这些尘埃颗粒是由脉冲引起的冲击在扩展的大气中形成的。对于碳星，无定形碳颗粒驱动的外流的详细模型与观测结果非常一致。一些仍然存在的差异可能是由于对激波冷却的简化处理、颗粒相对于气体的漂移、或巨大对流单体或尘埃诱导的斑图形成的影响。对于C/O < 1的恒星，最近的模型表明硅酸盐尘埃的吸收可能不足以驱动它们的风。一种可能的替代方法是通过半径为零点几微米的不含Fe的硅酸盐颗粒进行散射。在这种情况下，人们应该期望较少的拱星红化的M-和S-型AGB星比C-星具有可比的恒星参数和质量损失率。
英文摘要：
There are strong observational indications that the dense slow winds of cool luminous AGB stars are driven by radiative pressure on dust grains which form in the extended atmospheres resulting from pulsation-induced shocks. For carbon stars, detailed models of outflows driven by amorphous carbon grains show good agreement with observations. Some still existing discrepancies may be due to a simplified treatment of cooling in shocks, drift of the grains relative to the gas, or effects of giant convection cells or dust-induced pattern formation. For stars with C/O < 1, recent models indicate that absorption by silicate dust is probably insuffcient to drive their winds. A possible alternative is scattering by Fe-free silicate grains with radii of a few tenths of a micron. In this scenario one should expect less circumstellar reddening for M- and S-type AGB stars than for C-stars with comparable stellar parameters and mass loss rates.
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