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
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.