寻找II型针状体的盘对应物中的高速度
Search for high velocities in the disk counterpart of type II spicules
摘要：
最近，De Pontieu等人（2007 b）发现了一类针状体，其演化速度比以前已知的针状体更快，快速视运动速度为50- 150 km/s ${}^{-1}$，厚度为几百km，寿命为10- 60秒。由于有限的时空和热分辨率，这些所谓的II型针状体一直难以研究。在这里，我们使用IBIS仪器寻找高速度的磁盘对应的II型针状体。我们已经检测到快速演变的事件，其寿命不到一分钟，通常等于乐器的节奏（19秒）。这些事件的特点是多普勒频移，只出现在蓝色翼的钙II红外线。此外，空间范围，寿命和网络附近的位置，都表明与II型骨针的联系。然而，测得的多普勒速度的幅度明显低于在肢体处看到的明显运动。我们使用蒙特卡罗模拟表明，这种差异可以解释的前向模型中，在这些事件中的高速流的磁盘上的可见性是有限的组合的视线投影和减少不透明度向上推进的等离子体，特别是在重连驱动的射流，由一个大致恒定的能量供应。
英文摘要：
Recently, De Pontieu et al. (2007b) discovered a class of spicules that evolves more rapidly than previously known spicules, with rapid apparent motions of 50--150 km s${}^{-1}$, thickness of a few 100 km, and lifetimes of order 10--60 seconds. These so-called type II spicules have been difficult to study because of limited spatio-temporal and thermal resolution. Here we use the IBIS instrument to search for the high velocities in the disk counterpart of type II spicules. We have detected rapidly evolving events, with lifetimes that are less than a minute and often equal to the cadence of the instrument (19 secs). These events are characterized by a Doppler shift that only appears in the blue wing of the Ca II IR line. Furthermore the spatial extent, lifetime, and location near network, all suggest a link to type II spicules. However, the magnitude of the measured Doppler velocity is significantly lower than the apparent motions seen at the limb. We use Monte Carlo simulations to show that this discrepancy can be explained by a forward model in which the visibility on the disk of the high-velocity flows in these events is limited by a combination of line-of-sight projection and reduced opacity in upward propelled plasma, especially in reconnection driven jets that are powered by a roughly constant energy supply.
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