标题： 塑造A型恒星的核心发电机：偶极化石磁场的作用 显示英文标题

标题： Shaping core dynamos in A-type stars: The role of dipolar fossil fields

摘要： 天琴座Ap/Bp型星的大规模磁场在长时间尺度上是稳定的，并且通常具有简单的偶极子几何结构，这导致了化石起源的想法。 这些恒星还预计拥有能够产生强烈发电机作用的对流核。 我们旨在研究由恒星对流核发电机产生的磁场与类似已观测到的天琴座Ap/Bp型星磁拓扑结构的偶极子化石场之间的相互作用。 我们使用了一个$2.2M_\odot$型恒星的数值三维“盒中恒星”模拟，其中恒星核心包含了$20\%$倍的恒星半径。 作为初始条件，我们施加了两种纯粹的矢量配置，两者表面偶极强度均为6kG，并探索了不同的倾斜角度$\beta$（磁轴与自转轴之间的夹角），范围从$0^\circ$到$90^\circ$。 在恒星内部没有闭合磁力线的纯矢量场的加入，不会对核心发电机产生显著影响。 所有磁力线在恒星内部闭合的偶极子配置可以增强发电机，产生一种超能量平衡的准稳态解，其中磁场能量比动能强5倍。 增强的核心发电机具有典型磁场强度在105至172kG之间，磁场强度与$\beta$呈反比关系。 强烈的磁场在辐射包层中产生几乎刚性的旋转，并将核心的差速自转从太阳型改变为反太阳型。 唯一不稳定并衰减的情况是那些具有$\beta = 90^\circ$的偶极子。 在其余情况下，核心发电机被增强，表面磁场保持简单拓扑结构，与观测一致。 显示英文摘要

摘要： Large-scale magnetic fields of Ap/Bp stars are stable over long timescales and have typically simple dipolar geometries, leading to the idea of a fossil origin. These stars are also expected to have convective cores that can host strong dynamo action. We aim to study the interaction between the magnetic fields generated by the convective core dynamo of the star, and a dipolar fossil field reminiscent of observed magnetic topologies of Ap/Bp stars. We use numerical 3D star-in-a-box simulations of a $2.2M_\odot$ A-type star, where the core encompasses $20\%$ of the stellar radius. As an initial condition, we impose two purely poloidal configurations, both with a surface dipolar strength of 6 kG, and we explore different obliquity angles $\beta$ (the angle between the magnetic and rotational axes), ranging from $0^\circ$ to $90^\circ$. The inclusion of a poloidal field where none of the magnetic field lines are closed inside the star, does not affect the core dynamo in a significant way. Dipolar configurations where all the field lines are closed inside the star can enhance the dynamo, producing a superequipartition quasi-stationary solution, where the magnetic energy is 5 times stronger than the kinetic energy. The enhanced core dynamos have typical magnetic field strengths between 105 and 172 kG, where the strength has an inverse relation with $\beta$. The strong magnetic fields produce an almost rigid rotation in the radiative envelope, and change the differential rotation of the core from solar-like to anti-solar. The only cases where the imposed dipoles are unstable and decay are those with $\beta = 90^\circ$. In the rest of cases, the core dynamos are enhanced and the surface magnetic field survives keeping simple topologies like in the observations.