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 $\theta = 67 \pm 3^{\circ}$. The multi-wavelength polarisation can be adequately replicated by compact, spherical dust grains (i.e. from Mie theory) that are around 1.2 $\mu$m in size, assuming astronomical silicate composition, or 3.9 $\mu$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.

中文翻译：

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HD 172555 的极化和辐射传输建模

最近，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对 HD 172555 周围的碎片盘进行了成像。在这里，我们展示了高精度偏振仪 (HIPPI) 及其后续 HIPPI-2 在英澳望远镜上对 HD 172555 的光学孔径偏振测量。我们试图通过将我们的偏振测量与可用的红外和毫米光度测量相结合来对圆盘的散射光和连续发射进行建模，从而细化对圆盘组成尘埃颗粒的约束。我们使用 3D 辐射传输代码 Hyperion 对圆盘进行建模，假设圆盘的方向和范围是从 SPHERE 观测中获得的。修正星际介质贡献后，我们的多波长 HIPPI/-2 观测（幅度和方向）与最近的 SPHERE 偏振测量一致，其中部分偏振 $p = 62.4 \pm 5.2$~ppm 在 722.3 nm，位置角 $\theta = 67 \pm 3^{\circ}$。多波长极化可以通过紧凑的球形尘埃颗粒（即来自 Mie 理论）充分复制，假设为天文硅酸盐成分，其尺寸约为 1.2 $\mu$m，或者假设成分来自于 3.9 $\mu$m盘的辐射传递建模。因此，我们能够使用单个晶粒组成模型和尺寸分布来重现空间分辨的圆盘发射和极化。2$~ppm 在 722.3 nm，位置角 $\theta = 67 \pm 3^{\circ}$。多波长极化可以通过紧凑的球形尘埃颗粒（即来自 Mie 理论）充分复制，假设为天文硅酸盐成分，其尺寸约为 1.2 $\mu$m，或者假设成分来自于 3.9 $\mu$m盘的辐射传递建模。因此，我们能够使用单个晶粒组成模型和尺寸分布来重现空间分辨的圆盘发射和极化。2$~ppm 在 722.3 nm，位置角 $\theta = 67 \pm 3^{\circ}$。多波长极化可以通过紧凑的球形尘埃颗粒（即来自 Mie 理论）充分复制，假设为天文硅酸盐成分，其尺寸约为 1.2 $\mu$m，或者假设成分来自于 3.9 $\mu$m盘的辐射传递建模。因此，我们能够使用单个晶粒组成模型和尺寸分布来重现空间分辨的圆盘发射和极化。9 $\mu$m 假设从光盘的辐射传输模型得出的成分。因此，我们能够使用单个晶粒组成模型和尺寸分布来重现空间分辨的圆盘发射和极化。9 $\mu$m 假设从光盘的辐射传输模型得出的成分。因此，我们能够使用单个晶粒组成模型和尺寸分布来重现空间分辨的圆盘发射和极化。