HD 172555的偏振和辐射转移模型
Polarimetric and radiative transfer modelling of HD 172555
摘要：
HD 172555周围的碎片盘最近由甚大望远镜的光谱偏振高对比度系外行星研究仪器在近红外偏振散射光中成像。在这里，我们提出了光学孔径偏振测量HD 172555的高精度偏振仪器（HIPPI），其继任者HIPPI-2的英澳望远镜。我们寻求完善光盘的组成尘埃颗粒的约束条件相结合，我们的偏振测量与可用的红外和毫米测光模型的散射光和连续发射光盘。我们使用3D辐射转移代码的光盘建模，假设从SPHERE观测获得的光盘的方向和范围。在对星际介质的贡献进行校正后，我们的多波长HIPPI/-2观测（幅度和方向）与最近的SPHERE偏振测量结果一致，其分数偏振$p = 62.4 \pm 5.2$ ~ppm在722.3 nm处，位置角为$θ= 67 \pm 3^{\circ}$。多波长的偏振可以被致密的球形尘埃颗粒（即米氏理论）充分复制，这些尘埃颗粒的大小约为1.2 $μ$ m，假设天文硅酸盐成分，或3.9 $μ$ m，假设来自圆盘的辐射转移模型的成分。因此，我们能够再现空间分辨光盘发射和偏振与一个单一的晶粒组成模型和尺寸分布。
英文摘要：
The debris disc around HD 172555 was recently imaged in near-infrared polarised scattered light by the Very Large Telescope's Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. Here we present optical aperture polarisation measurements of HD 172555 by the HIgh Precision Polarimetric Instrument (HIPPI), and its successor HIPPI-2 on the Anglo-Australian Telescope. We seek to refine constraints on the disc's constituent dust grains by combining our polarimetric measurements with available infrared and millimetre photometry to model the scattered light and continuum emission from the disc. We model the disc using the 3D radiative transfer code Hyperion, assuming the orientation and extent of the disc as obtained from the SPHERE observation. After correction for the interstellar medium contribution, our multi-wavelength HIPPI/-2 observations (both magnitude and orientation) are consistent with the recent SPHERE polarisation measurement with a fractional polarisation $p = 62.4 \pm 5.2$~ppm at 722.3 nm, and a position angle $θ= 67 \pm 3^{\circ}$. The multi-wavelength polarisation can be adequately replicated by compact, spherical dust grains (i.e. from Mie theory) that are around 1.2 $μ$m in size, assuming astronomical silicate composition, or 3.9 $μ$m assuming a composition derived from radiative transfer modelling of the disc. We were thus able to reproduce both the spatially resolved disc emission and polarisation with a single grain composition model and size distribution.
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