Polarization Observations: A Pioneering Probe of Grain Growth and Magnetic Fields in Circumstellar Disks

在非常年轻的恒星内核开始核聚变之前，行星形成于围绕恒星旋转的气体和尘埃盘中。其中一个最大的谜团是尘埃是如何从小的星际尘埃颗粒变成越来越大的物体的：从尘埃到原行星。目前，由于很难将尘埃颗粒的生长与其他影响分开，因此没有明确的证据表明尘埃在磁盘中生长。然而，最近的发现表明，尘埃颗粒发出偏振光。光的偏振光对尘埃颗粒的大小很敏感，这为研究尘埃的性质提供了一个新的窗口。研究小组在偏振光下观察圆盘，以比较尘埃颗粒的特性与圆盘的演变。通过这项研究，他们希望找到迈向行星的第一步的证据。此外，他们的推广计划将把这些极化观测带到更大的社区，主要是通过STEM研讨会、当地女孩的天文学夏令营和公开讲座。研究人员将回答四个关键问题：1)尘埃连续盘在（亚）毫米波段上的极化是由磁排列颗粒、辐射排列颗粒、机械排列颗粒还是尘埃散射主导的？ 2)如果磁排列尘埃颗粒在任何波长上都不占主导地位，我们是否可以使用分子线极化来测量磁盘磁场？3)极化发射揭示了圆盘的本征性质，特别是尘埃粒度；4)尘埃偏振观测所测得的星盘性质如何随时间变化？他们将创建一个模型工具包，其中包括一般条件下多种机制的磁盘极化。这项研究的结果对于理解美国国家科学基金会的阿塔卡马大型毫米波阵列所做的观察将是重要的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Planets form in the rotating disk of gas and dust that surround very young stars before nuclear fusion begins in their cores. One of the big mysteries is how that dust grows from small interstellar dust grains to larger and larger objects: from dust to protoplanets. At the moment, there is no clear evidence of dust growth in the disk due to the difficulties in separating dust grain growth from other effects. However, recent discoveries have shown that the dust grains emit polarized light. The polarization of light is sensitive to the dust grain size, so there is a new window into dust properties. The team is observing disks in polarized light to make a comparison of dust grains properties with disk evolution. With this study, they expect to find evidence of the first steps towards planets. In addition, their outreach plans will bring these polarization observations to a larger community, mainly through a STEM workshop, a local girls' astronomy summer camp, and public lectures.The investigators will answer four critical questions: 1) Is dust continuum disk polarization across the (sub)millimeter bands dominated by magnetically aligned grains, radiationally aligned grains, mechanically aligned grains or dust scattering, 2) If magnetically aligned dust grains are not dominant at any wavelength, can we use molecular line polarization to measure the disk magnetic field?; 3) What are the intrinsic disk properties, especially the dust grain size, revealed by the polarization emission?; and 4) How do the disk properties measured by dust polarization observations vary with time? They will create a model toolkit which includes disk polarization from multiple mechanisms under general conditions. The results of this research will be important for understanding observations made with the NSF's Atacama Large Millimeter Array.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.