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arXiv 2009.08991astro-ph.SRastro-ph.EP
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帕克太阳探测器观测到的太阳风Angular Momentum通量

The Solar Wind Angular Momentum Flux as Observed by Parker Solar Probe

Adam J. Finley, Sean P. Matt, Victor Réville, Rui F. Pinto, Mathew Owens, Justin C. Kasper, Kelly E. Korreck, A. W. Case, Michael L. Stevens, Phyllis Whittlesey… 展开作者

Adam J. Finley, Sean P. Matt, Victor Réville, Rui F. Pinto, Mathew Owens, Justin C. Kasper, Kelly E. Korreck, A. W. Case, Michael L. Stevens, Phyllis Whittlesey, Davin Larson, Roberto Livi

摘要:

太阳自转周期的长期演化无法直接观测到,只能从其他类太阳恒星的自转周期来推断。假设太阳随着年龄的增长而向下旋转,按照旋转速率$\propto$年龄$^{-1/2}$,需要当前太阳角动量损失率大约为$6\times 10^{30}$ erg。磁流体动力学模型和以前对太阳风的观测(来自Helios和Wind航天器)通常分别预测接近$1\times 10^{30}$ erg或$3\times 10^{30}$ erg的a值。最近,帕克太阳探测器(PSP)观测到切向太阳风的速度高达$\sim50$公里/秒的局部地区的内日光层。如果这样的旋转流在整个日冕中普遍存在,这将意味着太阳风角动量损失率比之前所有的估计都要大一个数量级。在这封信中,我们评估的角动量通量的太阳风,使用的数据从前两个轨道的PSP。观测到的太阳风包含大的正角动量通量(如近日点期间所见)和负角动量通量。我们分析了两个太阳风流,PSP反复穿越,第一个是一个缓慢的风流,其平均角动量通量波动之间的积极到消极的,第二个是一个中速流包含一个积极的角动量通量(更符合恒定流的角动量)。当对PSP的数据进行整体评估时,平均赤道角动量通量意味着全球角动量损失率约为$2.6-4.2\times 10^{30}$ erg(这与以前航天器的观测结果更为一致)。

英文摘要:

The long-term evolution of the Sun's rotation period cannot be directly observed, and is instead inferred from trends in the measured rotation periods of other Sun-like stars. Assuming the Sun spins-down as it ages, following rotation rate $\propto$ age$^{-1/2}$, requires the current solar angular momentum-loss rate to be around $6\times 10^{30}$erg. Magnetohydrodynamic models, and previous observations of the solar wind (from the Helios and Wind spacecraft), generally predict a values closer to $1\times 10^{30}$erg or $3\times 10^{30}$erg, respectively. Recently, the Parker Solar Probe (PSP) observed tangential solar wind speeds as high as $\sim50$km/s in a localized region of the inner heliosphere. If such rotational flows were prevalent throughout the corona, it would imply that the solar wind angular momentum-loss rate is an order of magnitude larger than all of those previous estimations. In this letter, we evaluate the angular momentum flux in the solar wind, using data from the first two orbits of PSP. The solar wind is observed to contain both large positive (as seen during perihelion), and negative angular momentum fluxes. We analyse two solar wind streams that were repeatedly traversed by PSP; the first is a slow wind stream whose average angular momentum flux fluctuates between positive to negative, and the second is an intermediate speed stream containing a positive angular momentum flux (more consistent with a constant flow of angular momentum). When the data from PSP is evaluated holistically, the average equatorial angular momentum flux implies a global angular momentum-loss rate of around $2.6-4.2\times 10^{30}$ erg (which is more consistent with observations from previous spacecraft).

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