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

行星形成于围绕着非常年轻的恒星的气体和尘埃的旋转盘中，在它们的核心开始核聚变之前。 最大的谜团之一是尘埃如何从小的星际尘埃颗粒成长为越来越大的物体：从尘埃到原行星。 目前，由于难以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。 光的偏振对尘埃颗粒的大小很敏感，因此有一个了解尘埃性质的新窗口。 该团队正在偏振光下观察圆盘，以比较尘埃颗粒的性质与圆盘的演化。 通过这项研究，他们希望找到通往行星的第一步的证据。 此外，他们的外展计划将把这些偏振观测带到更大的社区，主要是通过STEM研讨会，当地女孩天文学夏令营和公开讲座。调查人员将回答四个关键问题：1）尘埃连续介质盘的偏振是否在（亚）毫米波段由磁性排列的颗粒、辐射排列的颗粒、机械排列的颗粒或尘埃散射主导，2）如果磁性排列的尘埃颗粒在任何波长下都不占优势，我们是否可以使用分子线偏振来测量磁盘磁场？3)偏振发射揭示的尘埃盘的固有性质，特别是尘埃颗粒的大小是什么？（4）尘埃偏振观测所测得的尘埃盘性质随时间的变化规律如何？ 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的观测结果非常重要。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.