渐近巨星分支恒星米拉A的一次巨型磁爆发
A giant magnetic eruption from the asymptotic giant branch star Mira A
浏览论文内容
中文总结 AI 辅助
本研究通过ALMA偏振观测证实，米拉A的巨型质量抛射由磁驱动而非尘埃辐射压，表明磁爆发可主导演化恒星的质量损失，需纳入AGB星风模型。
中文摘要 AI 辅助
低质量和中等质量恒星演化晚期的质量损失传统上归因于尘埃驱动的星风，而磁场的影响仍未得到充分约束。但近期观测显示，邻近的渐近巨星分支（AGB）恒星米拉A（Mira A）存在大量定向质量抛射，这些抛射似乎并非由尘埃上的辐射压驱动。我们通过观测研究磁场是否是米拉A质量抛射的成因：利用阿塔卡马大型毫米波/亚毫米波阵列（ALMA）获取了215 GHz下SiO v=1、J=5→4脉泽跃迁的全偏振观测数据，角分辨率为1.5-2.6天文单位。观测结果显示，存在一个由强偏振SiO脉泽追踪的高度磁化环状质量抛射，延伸至约8倍恒星半径处。其形态、偏振模式、能量学和运动学特征表明，这是一次类似恒星日冕物质抛射的磁驱动爆发。该观测证实，磁爆发可主导演化恒星的质量损失，意味着磁场必须成为未来AGB及其他冷巨星星风模型的核心组成部分。
英文摘要
Mass loss during the advanced evolutionary stages of low- and intermediate-mass stars is traditionally attributed to dust-driven winds, whereas the influence of magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB) star Mira~A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO $v=1$, $J=5\rightarrow4$ maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that magnetic eruptions can dominate mass loss from evolved stars and imply that magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.
