Cunnyngham Ian, Emilio Marcelo, Kuhn Jeff, Scholl Isabelle, Bush Rock
Institute for Astronomy, University of Hawaii, 34 Ohia Ku Street, Pukalani, Maui, Hawaii 96790, USA.
Ponta Grossa State University, Ponta Grossa, Parana 84030-900, Brazil.
Phys Rev Lett. 2017 Feb 3;118(5):051102. doi: 10.1103/PhysRevLett.118.051102.
The Sun's internal rotation Ω(r,Θ) has previously been measured using helioseismology techniques and found to be a complex function of colatitude θ and radius r. From helioseismology and observations of apparently "rooted" solar magnetic tracers, we know that the surface rotates more slowly than much of the interior. The cause of this slow-down is not understood, but it is important for understanding stellar rotation generally and any plausible theory of the solar interior. A new analysis using 5-min solar p-mode limb oscillations as a rotation "tracer" finds an even larger velocity gradient in a thin region at the top of the photosphere. This shear occurs where the solar atmosphere radiates energy and angular momentum. We suggest that the net effect of the photospheric angular momentum loss is similar to Poynting-Robertson "photon braking" on, for example, Sun-orbiting dust. The resultant photospheric torque is readily computed and, over the Sun's lifetime, is found to be comparable to the apparent angular momentum deficit in the near-surface shear layer.
太阳的内部自转Ω(r,Θ)此前已通过日震学技术进行测量，发现它是余纬θ和半径r的复杂函数。从日震学以及对明显“扎根”的太阳磁示踪物的观测中，我们知道太阳表面的旋转速度比其大部分内部区域要慢。这种减速的原因尚不清楚，但对于全面理解恒星自转以及任何合理的太阳内部理论而言都很重要。一项新的分析将5分钟的太阳p模边缘振荡用作自转“示踪物”，发现在光球层顶部的一个薄区域内存在更大的速度梯度。这种切变发生在太阳大气辐射能量和角动量的地方。我们认为，光球层角动量损失的净效应类似于例如对绕日尘埃的坡印廷－罗伯逊“光子制动”。由此产生的光球层扭矩很容易计算出来，并且在太阳的整个寿命期间，发现它与近表面剪切层中明显的角动量亏损相当。
