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arXiv 0905.3719astro-ph.SR
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太阳能颗粒化中超音速水平流的探测

Detection of supersonic horizontal flows in the solar granulation

L. R. Bellot Rubio

摘要:

颗粒对流的流体动力学模拟预测在任何时候都存在覆盖太阳表面约3-4%的超音速流,但这些流尚未被明确地检测到。使用的分光偏振仪搭载的日之出卫星的数据,我提出了直接的证据,快速水平等离子体运动在安静的太阳颗粒。由于更有利的观察条件,它们的可见度向肢体增加。在日出分辨率下,水平气流产生了不对称的强度分布,具有非常倾斜的蓝色机翼,甚至是位于主要吸收特征蓝色方向的线卫星。在明亮颗粒的边缘观察到高达9 km/s的多普勒频移,表明流动达到超音速。最强的速度出现在0.5弧秒或更小的斑块中,它们往往与增强的连续强度、线宽和等效宽度有关,但是这些参数的大值并不一定意味着超音速流的存在。时间序列的光谱偏振测量区域远离磁盘中心显示的瞬态性质的强水平运动,持续时间只有一小部分的颗粒寿命。超音速流预计会在颗粒和颗粒间通道的边界处产生激波,也可能在安静的太阳互联网区域出现小规模磁场方面发挥作用。

英文摘要:

Hydrodynamic simulations of granular convection predict the existence of supersonic flows covering ~3-4% of the solar surface at any time, but these flows have not been detected unambigously as yet. Using data from the spectropolarimeter aboard the Hinode satellite, I present direct evidence of fast horizontal plasma motions in quiet Sun granules. Their visibility increases toward the limb due to more favorable viewing conditions. At the resolution of Hinode, the horizontal flows give rise to asymmetric intensity profiles with very inclined blue wings and even line satellites located blueward of the main absorption feature. Doppler shifts of up to 9 km/s are observed at the edges of bright granules, demonstrating that the flows reach supersonic speeds. The strongest velocities occur in patches of 0.5 arcsec or less. They tend to be associated with enhanced continuum intensities, line widths, and equivalent widths, but large values of these parameters do not necessarily imply the existence of supersonic flows. Time series of spectropolarimetric measurements in regions away from disk center show the transient nature of the strong horizontal motions, which last only for a fraction of the granule lifetime. Supersonic flows are expected to produce shocks at the boundaries between granules and intergranular lanes, and may also play a role in the emergence of small-scale magnetic fields in quiet Sun internetwork regions.

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