Spectral Tomography of Ultra-Cool Dwarf Radio Magnetospheres

该项目的主要科学目标是确定极低质量恒星的磁场结构。这项研究将扩大我们对恒星中磁场是如何产生的理解，这一点目前还不是很清楚。这也有助于我们理解太阳磁场，它在太阳活动高峰期到达地球的潜在破坏性太阳磁暴中扮演着关键角色。该项目将为天文学专业代表性不足的学生提供研究生培训机会。这个项目的结果将被整合到PI.正在开发的一门新的本科课程中。这项提议解决了恒星天体物理学中的一个基本问题：在极小质量的恒星中，令人惊讶的强大日冕磁场的性质是什么？研究计划包括两个部分。第一个是一个观测计划，以确定选定的超冷矮星样本的动态光谱，这些样本显示出脉冲射电发射。观测将利用超大型阵列获得几个时期的宽带光谱，以确定脉冲周期、偏振和形态的稳定性。第二部分是开发一个真实的磁层模型，它将被用来创建合成的宽带频谱。该模型将包括几个以前没有考虑过的等离子体物理效应，如冷等离子体射线跟踪和密度耗尽空穴引起的角度光束。这项名为光谱层析成像的计划将把合成的动态光谱与观测结果进行比较，以限制恒星磁层的几何形状和等离子体性质。

The primary scientific goal of the project is to determine the structure of magnetic fields in very low-mass stars. This study will broaden our understanding of how magnetic fields are generated in stars, which is currently not well understood. This could also contribute to our understanding of the Sun's magnetic field, which plays a key role in the potentially damaging solar magnetic storms that reach Earth during periods of high solar activity. The program will provide a graduate training opportunity for a student from a group that is underrepresented in astronomy. Results from this program will be integrated into a new undergraduate course being developed by the PI.This proposal addresses a fundamental question in stellar astrophysics: What is the nature of the surprisingly strong coronal magnetic fields in very low-mass stars? The research program comprises two parts. The first is an observational program to determine the dynamical spectra of a selected sample of ultra-cool dwarf stars that exhibit pulsed radio emission. The observations will utilize the Very Large Array to obtain wideband spectra over several epochs to establish the stability of the pulse periods, polarization, and morphology. The second part is the development of a realistic magnetospheric model that will be used to create synthesized wideband spectra. The model will include several plasma physics effects that have not been previously considered, such as cold-plasma ray tracing and angular beaming caused by density-depleted cavities. This scheme, denoted spectral tomography, will compare synthetic dynamic spectra with observations to constrain the geometry and plasma properties of the stellar magnetospheres.