Variability of Accreting Magnetized Stars Studied with 3D MHD Simulations and 3D Radiative Transfer

通过 3D MHD 模拟和 3D 辐射传输研究吸积磁化恒星的变化

• 批准号: 0807129
• 负责人: Marina Romanova
• 金额: $ 56.6万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0807129&HistoricalAwards=false
• 关键词: Variability; Accreting; Magnetized; Stars; Studied

Accreting magnetized stars, such as Classical T Tauri stars, cataclysmic variables, and millisecond X-ray pulsars show a wide variety of variability in their light curves and spectra. In some cases, exact periodicity is observed, while in other cases the light curves show stochastic fluctuations or quasi-periodic oscillations. Understanding these magnetized stars requires global 3D magnetohydrodynamic (MHD) modeling. Recent 3D and 2.5D MHD simulations performed by Dr. Romanova and her collaborators have shown a wide variety of possible paths of matter flow around magnetized stars, including the possibility of direct accretion through the Rayleigh-Taylor instability. These investigations have shown that magnetized stars may be either in the stable or unstable regime of accretion, with strikingly different observational properties. This and other interesting phenomena found in their MHD simulations may describe different properties or stages of evolution of different accreting magnetized stars.However, to compare the results with observations, one needs to calculate continuum and line spectra from the stars and the surrounding matter. This requires high-level radiative transfer modeling, which is the primary goal of this project: to perform full 3D radiative transfer modeling, using the results of the 3D MHD simulations as a base. Results of such 3D (MHD) + 3D (radiative) models will be compared with observations of different Classical T Tauri stars for which spectral and photometric observational data are available. A number of new MHD simulations will be done aimed at understanding different phenomena around magnetized stars, including (1) accretion through instabilities; (2) modeling of outflows; (3) investigation of disk oscillations and warping generated by a misaligned dipole.It is expected that this research will be an important new step in modeling accreting magnetized stars. Two modern state-of-the-art codes (3D MHD and radiative transfer) will be combined in a major effort to understand the physics of magnetized stars. The results will be valuable for understanding the whole range of accreting magnetized stars, from magnetic brown dwarfs to neutron stars. The results on disk oscillations and warping will be valuable for understanding processes around compact stars. The methods and numerical MHD codes developed here also have general value and are applicable in other areas of science such as planetary science, geophysics, earth magnetospheric science and heliospheric science, and in engineering. The project is ideal for training young scientists - graduate and undergraduate students - who will learn magnetohydrodynamics and programming, how to parallelize the codes, and to write auxiliary programs. The project will also support a public exhibition at the Ithaca Sciencenter on the birth of stars featuring the roles of accretion and plasma physics.

吸积的磁化星，如经典金牛座T星、激变变星和毫秒X射线双星，在它们的光变曲线和光谱中表现出各种各样的变化。在某些情况下，观察到精确的周期性，而在其他情况下，光变曲线显示随机波动或准周期振荡。了解这些磁化恒星需要进行全球3D磁流体动力学（MHD）建模。Romanova博士和她的合作者最近进行的3D和2.5D MHD模拟显示了磁化恒星周围物质流动的各种可能路径，包括通过瑞利-泰勒不稳定性直接吸积的可能性。这些研究表明，磁化恒星可能处于稳定或不稳定的吸积状态，具有明显不同的观测特性。在他们的MHD模拟中发现的这一现象和其他有趣的现象可能描述了不同吸积磁化恒星的不同性质或演化阶段。然而，为了将结果与观测结果进行比较，需要计算恒星及其周围物质的连续谱和线谱。这需要高层次的辐射传输建模，这是该项目的主要目标：使用3D MHD模拟的结果作为基础，执行完整的3D辐射传输建模。这种3D（MHD）+ 3D（辐射）模型的结果将与不同的经典金牛座T星的光谱和光度观测数据的观测进行比较。我们将进行一系列新的MHD模拟，旨在理解磁化星周围的不同现象，包括（1）通过不稳定性的吸积;（2）外流的模拟;（3）研究由不对准偶极子产生的盘振荡和翘曲。预计这项研究将成为吸积磁化星模拟的重要新步骤。两个现代国家的最先进的代码（三维磁流体和辐射传输）将结合在一个重大的努力，以了解磁化恒星的物理。这些结果对于理解从磁褐矮星到中子星的整个吸积磁化星范围都很有价值。盘振荡和翘曲的结果将是有价值的理解致密星周围的过程。本文提出的方法和数值MHD程序也具有普遍的应用价值，可应用于行星科学、地球物理学、地球磁层科学、日光层科学和工程等其他科学领域。该项目是理想的培训年轻科学家-研究生和本科生-谁将学习磁流体力学和编程，如何并行化的代码，并编写辅助程序。该项目还将支持在伊萨卡科学中心举行的关于恒星诞生的公开展览，其中包括吸积和等离子体物理学的作用。