We present 3D MHD simulations of purely toroidal and mixed poloidal-toroidal magnetic field configurations to study the behavior of the Tayler instability. For the first time the simultaneous action of rotation and magnetic diffusion are taken into account and the effects of a poloidal field on the dynamic evolution of unstable toroidal magnetic fields is included. In the absence of diffusion, fast rotation (rotation rate compared to Alfvén frequency) is able to suppress the instability when the rotation and magnetic axes are aligned and when the radial field strength gradient p < 1.5. When diffusion is included, this system turns unstable for diffusion dominated and marginally diffusive dominated regions. If the magnetic and rotation axes are perpendicular to each other the stabilizing effect induced by the Coriolis force is scale dependent and decreases with increasing wavenumber. In toroidal fields with radial field gradients bigger than p > 1.5, rapid rotation does not suppress the instability but instead introduces a damping factor to the growth rate in agreement with the analytic predictions. For the mixed poloidal-toroidal fields we find an unstable axisymmetric mode, not predicted analytically, right at the stability threshold for the non-axisymmetric modes; it has been argued that an axisymmetric mode is necessary for the closure of the Tayler-Spruit dynamo loop.
Asteroseismic detection of a predominantly toroidal magnetic field in the deep interior of the main-sequence F star KIC 9244992
The University of Tokyo（东京大学）；University of Southern Queensland（南昆士兰大学）；North-West University（西北大学）；University of Lancashire（兰开夏大学）；Tohoku University（东北大学）
Magnetic fields have been observed in massive Ap/Bp stars and presumably are also present in the radiative zone of solar-like stars. Yet, to date there is no clear understanding of the dynamics of the magnetic field in stably stratified layers. A purely toroidal magnetic field configuration is known to be unstable, developing mainly non-axisymmetric modes. Rotation and a small poloidal field component may lead to a stable configuration. Here we perform global MHD simulations with the EULAG-MHD code to explore the evolution of a toroidal magnetic field located in a layer whose stratification re…
The single-valued parameter (SVP) method is a parametric method that offers the possibility of computing radiative accelerations in stellar interiors much faster than other methods. It has been implemented in a few stellar evolution numerical codes for about a decade. In the present paper, we describe improvements we have recently brought in the process of preparing, from atomic/opacity databases, the SVP tables that are needed to use the method, and their extension to a larger stellar mass domain (from 1 to 10 solar mass) on the main-sequence. We discuss the validity domain of the method. We …
Understanding mechanisms underlying solar cycle predictability with a general framework
School of Space and Earth Sciences, Beihang University（北京航空航天大学空间与地球科学学院）；Key Laborotary of Space Environment Monitoring and Information Processing of MIIT（工业和信息化部空间环境监测与信息处理重点实验室）
Massive stars are important metal factories in the Universe. They have short and energetic lives, and many of them inevitably explode as a supernova and become a neutron star or black hole. In turn, the formation, evolution and explosive deaths of massive stars impact the surrounding interstellar medium and shape the evolution of their host galaxies. Yet the chemical and dynamical evolution of a massive star, including the chemical yield of the ultimate supernova and the remnant mass of the compact object, strongly depend on the interior physics of the progenitor star. We currently lack empiri…
The possibility of measuring the internal rotation of the Sun and stars thanks to helio- and asteroseismology offers tremendous constraints on hydro- and magnetohydrodynamical processes acting in stellar interiors. Understanding the processes responsible for the transport of angular momentum in stellar interiors is crucial as they will also influence the transport of chemicals and thus the evolution of stars. Here we present some of the key results obtained in both fields and how detailed seismic analyses can provide stringent constraints on the physics of angular momentum transport in the int…
Rossby waves arise due to the conservation of total vorticity in rotating fluids and may govern the large-scale dynamics of stellar interiors. Recent space missions collected huge information about the light curves and activity of many stars, which triggered observations of Rossby waves in stellar surface and interiors. We aim to study the theoretical properties of Rossby waves in stratified interiors of uniformly rotating radiative stars with sub-adiabatic vertical temperature gradient. We use the equatorial beta-plane approximation and linear vertical gradient of temperature to study the lin…
Besides their causal connection with long and short-term magnetic variability, solar bipolar magnetic regions are our chief source of insight into the location, size, and properties of large-scale toroidal magnetic structures in the solar interior. The great majority of these regions (~95%) follow a systematic east-west polarity orientation (Hale's law) that reverses in opposite hemispheres and across even and odd cycles. These regions also present a systematic north-south polarity orientation (Joy's law) that helps build the poloidal field that seeds the new cycle. Exceptions to Hale's law ar…
Numerical simulations of magneto-convection have greatly expanded our understanding of stellar interiors and stellar magnetism. Recently, fully compressible hydrodynamical simulations of full-star models have demonstrated the feasibility of studying the excitation and propagation of pressure and internal gravity waves in stellar interiors, which would allow for a direct comparison with asteroseismological measurements. However, the impact of magnetic fields on such waves has not been taken into account yet in three-dimensional simulations. We conduct a proof of concept for the realization of t…
Turbulent Mixing and Nuclear Burning in Stellar Interiors
原子核的湍流燃烧是恒星演化过程中的一种常见现象。在这里，我们研究一个具有挑战性的情况下：合并的氖和氧燃烧壳层在23 M $_{\odot}$明星。一个以前未知的准稳态是由混合，湍流传输和核燃烧之间的相互作用建立的。由此产生的恒星结构有两个燃烧的外壳在一个对流区。我们发现，新的氖燃烧层覆盖了对流区的扩展区域，燃烧峰值发生在Damköhler数首次等于1的位置以下。这些特征不同于类似的摄入事件的一维恒星演化模型所预测的特征。我们开发的平均场湍流方程，治理成分的演变，并用它们来解释我们的数据集。一个重要的副产品是一种手段来量化亚网格尺度的数值水动力方案固有的影响。对于隐式大涡模拟，分析方法特别强大，因为它可以揭示模拟流在何处以及如何通过分辨率进行修改，并提供耗散或诱导输运效应的直接物理解释。专注于我们的分析的平均场组成方差方程，我们恢复了Kolmogorov率的湍流耗散没有它被强加，与以前的结果，使用湍流动能方程。
Excitation of gravity waves by fingering convection, and the formation of compositional staircases in stellar interiors
指状对流（英语：Fingering convection）是一种微弱但重要的混合现象，发生在稳定分层的恒星辐射带中，且存在反平均分子量梯度。Brown等人（2013）最近提出了一种新的指状对流混合模型，该模型不包含自由参数，并且发现几乎在所有情况下都符合直接数值模拟的结果。然而，值得注意的是，他们发现，在少数情况下，大规模的重力波，其次是热成分分层，从指状对流自发增长的混合大大增强了他们的预测值以上。这种效应在海洋学方面是众所周知的，并归因于所谓的“集体不稳定性”的激发。在这项工作中，我们建立在Brown et al.（2013）和Traxler et al.（2011 b）的结果基础上，以确定集体不稳定性可能发生的条件。我们发现，它只在恒星区域有一个相对较大的普朗特数（运动粘度的热扩散率的比率），$O(10^{-3})$或更大。这意味着集体不稳定性不会发生在主序星中，那里的普朗特数总是比这小得多（除了表面对流区的外层，那里的指进是无关紧要的）。原则上，它可以在高电子简并的区域，在He核心闪光期间，或在白矮星的内部被激发。我们讨论了我们的研究结果对这些对象的影响，无论是从理论上还是从观测的角度来看。
The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M$_\odot$ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against the poloidal field energy. These two branches divide stars above and below $\sim$ 0.5 M$_\odot$. We present here a novel method of…
The Beauty of k2: Probing Stellar Interiors Using Apsidal Motion. I. The Benchmark Massive Binary HD 152248
University of Geneva（日内瓦大学）；Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut（海德堡大学天文学中心，天文计算研究所）；Keele University（基尔大学）；Kavli IPMU (WPI), The University of Tokyo（东京大学 Kavli 宇宙粒子与宇宙学前沿研究中心（WPI））
Simulations of the onset and dynamical evolution of inertial waves in solar/stellar interior
Universidade Federal de Minas Gerais（米纳斯吉拉斯联邦大学）；Observatório Nacional（国家天文台）；Royal Observatory of Belgium（比利时皇家天文台）；High Altitude Observatory, NSF National Center for Atmospheric Research（美国国家大气研究中心高空观测站）；National Center for Atmospheric Research（美国国家大气研究中心）
One of the largest uncertainties in stellar structure and evolution theory is the transport of angular momentum in the stellar interiors. Asteroseismology offers a powerful tool for measuring the internal rotation frequencies of pulsating stars, but the number of such measurements has remained few for $\gtrsim 3\,{\rm M}_\odot$ main-sequence stars. In this work, we compile a list of 52 slowly pulsating B stars for which the interior rotation has been measured asteroseismically. The measurements of the spin parameters, which describe the relative importance of rotation, for the gravito-inertial…
The representation of magnetic field as a sum of a toroidal field and a poloidal field has not rarely been used in astrophysics, particularly in relation to stellar and planetary magnetism. In this representation, each toroidal field line lies entirely in a surface, which is named a toroidal field surface. The poloidal field is represented by the curl of another toroidal field and it threads a stack of toroidal field surfaces. If the toroidal field surfaces are either spheres or planes, the poloidal-toroidal (PT) representation is known to have a special property that the curl of a poloidal fi…
