标题： 低质量恒星碰撞过程中的磁场放大 显示英文标题

标题： Magnetic Field Amplification during Stellar Collisions between Low-Mass Stars

摘要： 蓝离散星是恒星团中一类较蓝且看似比其他成员更年轻的恒星子集，在其演化过程中似乎落后了一步。它们为理解宿主恒星团内的恒星动力学和恒星群体提供了一个独特的机会。在碰撞形成场景中，一个持续存在的挑战是碰撞产物中过高的角动量。随后在向稳定状态转变过程中的显著质量损失会导致一颗质量过低而无法成为蓝离散星的恒星，除非它能够有效地减速旋转。虽然许多提出的减速机制涉及通过碰撞产物内的磁制动增强角动量损失，但这些磁场的存在及其强度尚未得到证实。 在这里，我们报告了两次低质量主序星碰撞的三维磁流体力学模拟，并研究了磁场放大现象。磁场能量被放大了$10^{8}-10^{10}$倍，导致碰撞产物核心处的磁场强度达到$10^{7}-10^{8}$高斯，且与碰撞参数无关。表面磁场强度增加到$10-10^{4}$高斯。此外，在非轴向碰撞中，围绕碰撞产物出现了一个明显扁平化的旋转气体结构，这可能是盘状结构形成的线索。如此显著的磁场放大以及潜在的盘状结构形成表明，碰撞产物可能通过磁制动和磁盘锁定实现有效的减速，从而使其表现为蓝离散星。 显示英文摘要

摘要： Blue straggler stars in stellar clusters are a subset of stars that are bluer and appear younger than other cluster members, seemingly straggling behind in their evolution. They offer a unique opportunity to understand the stellar dynamics and populations within their hosts. In the collisional formation scenario, a persistent challenge is the excessive angular momentum in the collision product. The consequent significant mass loss during transition to a stable state leads to a star with too low a mass to be a blue straggler, unless it spins down efficiently. While many proposed spin-down mechanisms involve boosted angular momentum loss via magnetic braking within the collision product, the existence or strength of these magnetic fields has not been confirmed. Here, we report three-dimensional magnetohydrodynamical simulations of collisions between two low-mass main-sequence stars and investigate magnetic field amplification. Magnetic field energy is amplified by a factor of $10^{8}-10^{10}$, resulting in the magnetic field strength of $10^{7}-10^{8}$G at the core of the collision product, independent of collision parameters. The surface magnetic field strengths have increased up to $10-10^{4}$ G. In addition, a distinctly flattened, rotating gas structure appears around the collision products in off-axis collisions, which may be a hint of possible disk formation. Such significant magnetic amplification and potential disk formation suggest the possibility of efficient spin-down of collision products via magnetic braking and magnetic disk locking, which can result in their appearance as blue stragglers.