HD142527：采用SPHERE的定量圆盘旋光法
HD142527: Quantitative disk polarimetry with SPHERE
摘要：
我们提出了高精度的测光和旋光测量的原行星盘周围的HD 142527，重点是确定尘埃的光散射参数。我们重新整理了来自SPHERE/VLT的ZIMPOL和IRDIS子仪器的HD 142527在VBB（735 nm）和H波段（1625 nm）的偏振微分成像数据。利用基于参考星差分成像的偏振测量和光度测量方法，可以高精度地测量星周盘散射光的线偏振强度和总强度。我们使用简单的蒙特卡罗模拟多个光散射的磁盘表面推导出的尘埃的三个散射参数的限制：最大偏振的$P_{\rm max}$，不对称参数$g$，和单散射的$ω$。我们分别在VBB和H波段测量$51.4\pm1.5$ mJy和$206\pm12$ mJy的反射总强度以及$11.3\pm0.3$ mJy和$55.1\pm3.3$ mJy的偏振强度。我们还发现，在视觉范围内的偏振度之间的$28\%$远侧的磁盘和$17\%$近侧的变化。圆盘显示出散射光强度和偏振强度的红色，当与视觉相比时，近红外中的散射光强度和偏振强度大约是视觉的两倍。我们确定与模型计算的尘埃粒子的散射特性，并找到证据，为强前向散射（$g\approx 0.5-0.75$），相对较低的单散射（$ω\approx 0.2-0.5$），和高的最大偏振（$P_{\rm max} \approx 0.5-0.75$）在表面上的远侧的磁盘上的两个观察到的波长。光学参数表明存在大的聚集尘埃粒子，这是必要的解释高的最大偏振，强前向散射性质的尘埃，和观察到的红色磁盘的颜色。
英文摘要：
We present high-precision photometry and polarimetry for the protoplanetary disk around HD142527, with a focus on determining the light scattering parameters of the dust. We re-reduced polarimetric differential imaging data of HD142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS subinstruments of SPHERE/VLT. With polarimetry and photometry based on reference star differential imaging, we were able to measure the linearly polarized intensity and the total intensity of the light scattered by the circumstellar disk with high precision. We used simple Monte Carlo simulations of multiple light scattering by the disk surface to derive constraints for three scattering parameters of the dust: the maximum polarization of $P_{\rm max}$, the asymmetry parameter $g$, and the single-scattering albedo $ω$. We measure a reflected total intensity of $51.4\pm1.5$ mJy and $206\pm12$ mJy and a polarized intensity of $11.3\pm0.3$ mJy and $55.1\pm3.3$ mJy in the VBB and H-band, respectively. We also find in the visual range a degree of polarization that varies between $28\%$ on the far side of the disk and $17\%$ on the near side. The disk shows a red color for the scattered light intensity and the polarized intensity, which are about twice as high in the near-infrared when compared to the visual. We determine with model calculations the scattering properties of the dust particles and find evidence for strong forward scattering ($g\approx 0.5-0.75$), relatively low single-scattering albedo ($ω\approx 0.2-0.5$), and high maximum polarization ($P_{\rm max} \approx 0.5-0.75$) at the surface on the far side of the disk for both observed wavelengths. The optical parameters indicate the presence of large aggregate dust particles, which are necessary to explain the high maximum polarization, the strong forward-scattering nature of the dust, and the observed red disk color.
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