论文标题

来自低质量星星I的Alfvén-Wave驱动的磁旋转器风:磁制动和质量损坏速率的旋转依赖性

Alfvén-wave driven magnetic rotator winds from low-mass stars I: rotation dependences of magnetic braking and mass-loss rate

论文作者

Shoda, Munehito, Suzuki, Takeru K., Matt, Sean P., Cranmer, Steven R., Vidotto, Aline A., Strugarek, Antoine, See, Victor, Réville, Victor, Finley, Adam J., Brun, Allan Sacha

论文摘要

恒星旋转的观察结果表明,低质量恒星在主序列中失去角动量。我们以一系列旋转速率模拟了类似太阳恒星的风,涵盖了快速和慢速磁电机旋转器机制,包括两者之间的过渡。我们概括了一个Alfvén-Wave驱动的太阳风模型,该模型通过明确包括磁铁中心力来建立在以前的作品上。在此模型中,假定表面平均的开放磁通量缩放为$ b_ \ ast f^{\ rm open} _ \ ast \ ast \ propto {\ rm ro}^{ - 1.2} $,其中$ f^{\ f^{\ rm Open} _ \ ast $和$ ro rm ro {我们发现,1。风的角动量损耗率(扭矩)被描述为$τ_W\约2.59 \ times 10^{30} {\ rm \ erg \ erg} \ \ lesge(ω__\ ast /ω__\ ast /ω_\ odot \ odot \ odot \ odot \ right) t^{ - 0.55} $。 2。质量损失率在$ \ dot {m} _W \ sim 3.4 \ times 10^{ - 14} m_ \ odot {\ rm \ yr \ yr^{ - 1}} $,由于alfvén波的强烈反射和散发,因此在成色素圈中。这表明染色体在连接恒星表面和恒星风中具有很大的影响。同时,风电压压力缩放为$ p_w \ proptoω__\ ast^{0.57} $,它能够解释Wood等人观察到的恒星风的下层。 3。显示Alfvén半径的位置以与一维分析理论一致的方式扩展。此外,Alfvén半径的精确缩放与使用热驱动风的先前作品相匹配。我们的结果表明,在主序列期间,Alfvén-Wave驱动的磁性旋转器风在恒星旋转中起主要作用。

Observations of stellar rotation show that low-mass stars lose angular momentum during the main sequence. We simulate the winds of Sun-like stars with a range of rotation rates, covering the fast and slow magneto-rotator regimes, including the transition between the two. We generalize an Alfvén-wave driven solar wind model that builds on previous works by including the magneto-centrifugal force explicitly. In this model, the surface-averaged open magnetic flux is assumed to scale as $B_\ast f^{\rm open}_\ast \propto {\rm Ro}^{-1.2}$, where $f^{\rm open}_\ast$ and ${\rm Ro}$ are the surface open-flux filling factor and Rossby number, respectively. We find that, 1. the angular momentum loss rate (torque) of the wind is described as $τ_w \approx 2.59 \times 10^{30} {\rm \ erg} \ \left( Ω_\ast / Ω_\odot \right)^{2.82}$, yielding a spin-down law $Ω_\ast \propto t^{-0.55}$. 2. the mass-loss rate saturates at $\dot{M}_w \sim 3.4 \times 10^{-14} M_\odot {\rm \ yr^{-1}}$, due to the strong reflection and dissipation of Alfvén waves in the chromosphere. This indicates that the chromosphere has a strong impact in connecting the stellar surface and stellar wind. Meanwhile, the wind ram pressure scales as $P_w \propto Ω_\ast^{0.57}$, which is able to explain the lower-envelope of the observed stellar winds by Wood et al. 3. the location of the Alfvén radius is shown to scale in a way that is consistent with 1D analytic theory. Additionally, the precise scaling of the Alfvén radius matches previous works which used thermally-driven winds. Our results suggest that the Alfvén-wave driven magnetic rotator wind plays a dominant role in the stellar spin-down during the main-sequence.

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