Context. Theory surrounding the origin of the dust-laden winds from evolved stars remains mired in controversy. Characterizing the formation loci and the dust distribution within approximately the first stellar radius above the surface is crucial for understanding the physics that underlie the mass-loss phenomenon. Aims. By exploiting interferometric polarimetry, we derive the fundamental parameters that govern the dust structure at the wind base of a red supergiant. Methods. We present near-infrared aperture-masking observations of Betelgeuse in polarimetric mode obtained with the NACO/SAMPol instrument. We used both parametric models and radiative transfer simulations to predict polarimetric differential visibility data and compared them to SPHERE/ZIMPOL measurements. Results. Using a thin dust shell model, we report the discovery of a dust halo that is located at only 0.5 R _(?)above the photosphere (i.e. an inner radius of the dust halo of 1.5 R _(?)). By fitting the data under the assumption of Mie scattering, we estimate the grain size and density for various dust species. By extrapolating to the visible wavelengths using radiative transfer simulations, we compare our model with SPHERE/ZIMPOL data and find that models based on dust mixtures that are dominated by forsterite are most favored. Such a close dusty atmosphere has profound implications for the dust formation mechanisms around red supergiants.
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机译:上下文。围绕着来自演化恒星的充满尘埃的风的起源的理论仍然陷入争议。在地表以上大约第一恒星半径内,表征地层轨迹和尘埃分布对于了解构成质量损失现象基础的物理学至关重要。目的通过利用干涉偏振法,我们得出了控制红色超巨人风基处尘埃结构的基本参数。方法。我们目前用NACO / SAMPol仪器获得的偏光模式下Betelgeuse的近红外光圈掩盖观察。我们使用参数模型和辐射传输模拟来预测偏振差分可见性数据,并将其与SPHERE / ZIMPOL测量进行比较。结果。使用薄的尘埃壳模型,我们报告发现了一个位于光球上方仅0.5 R _(?)的尘埃晕(即尘埃晕的内半径为1.5 R _(?))。通过在米氏散射假设下拟合数据,我们估算了各种粉尘种类的晶粒尺寸和密度。通过使用辐射转移模拟推断可见波长,我们将我们的模型与SPHERE / ZIMPOL数据进行了比较,发现最受基于镁橄榄石为主的粉尘混合物的模型。这样的尘土飞扬的气氛对红色超巨星周围的尘埃形成机制具有深远的影响。
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