STEREO观测到的C/2011 L4彗星发射的高速瞬逝团动力学
Dynamics of High-Velocity Evanescent Clumps [HVECs] Emitted from Comet C/2011 L4 as Observed by STEREO
摘要：
来自STEREO-B上SECCHI/HI-1望远镜的高质量白光图像显示了从C/2011 L4 [Pan-STARRS]彗星的彗发中排出的高速瞬逝团块[HVECs]。动画图像提供了高度动态的喷出物在反太阳方向近径向移动的证据。在HI 1-B图像中最初检测到的团块的整体速度范围从$200-400$ km s $^{-1}$，随后是明显的加速，最高速度为$450-600$ km s $^{-1}$，这是典型的缓慢到中等太阳风速度。团块速度不超过这些极限值，似乎达到一个平台。图像还显示，这些团块在传播时不会膨胀。数量级计算表明，电离的单个原子或分子与观测相比加速得太快，而微米或更大的尘埃颗粒加速得太慢。我们发现中性Na、Li、K或Ca原子与$β>50$的配合物可能符合观测结果。同样可能的是，我们发现太阳风和日光层磁场（HMF）的相互作用可以导致观察到的团块动力学演化，使它们迅速加速到太阳风的速度。因此，我们推测HVECs是由带电粒子（尘埃粒子）或中性原子加速辐射压力在$β>50$值。此外，数据表明，团块喷出物最初沿着近径向的明亮结构移动，然后分离成HVEC和较大的尘埃颗粒，由于太阳辐射和重力的影响，这些尘埃颗粒相对于彗星的轨道运动稳定地向后弯曲。这些结构逐渐在尘埃尾部形成新的条纹。条纹的近周期性间隔可能表明由于彗星核的旋转而引起的释气活动调制。然而，目前还不清楚是否所有的条纹都是由于这个过程而形成的。
英文摘要：
High-quality white-light images from the SECCHI/HI-1 telescope onboard STEREO-B reveal high-velocity evanescent clumps [HVECs] expelled from the coma of the C/2011 L4 [Pan-STARRS] comet. Animated images provide evidence of highly dynamic ejecta moving near-radially in the anti-sunward direction. The bulk speed of the clumps at their initial detection in the HI1-B images range from $200-400$ km s$^{-1}$ followed by an appreciable acceleration up to speeds of $450-600$ km s$^{-1}$, which are typical of slow to intermediate solar wind speeds. The clump velocities do not exceed these limiting values and seem to reach a plateau. The images also show that the clumps do not expand as they propagate. Order of magnitude calculations show that ionized single atoms or molecules accelerate too quickly compared to observations, while dust grains micron sized or larger accelerate too slowly. We find that neutral Na, Li, K, or Ca atoms with $β>50$ could possibly fit the observations. Just as likely, we find that an interaction with the solar wind and the heliospheric magnetic field (HMF) can cause the observed clump dynamical evolution, accelerating them quickly up to solar wind velocities. We thus speculate that the HVECs are composed of charged particles (dust particles) or neutral atoms accelerated by radiation pressure at $β>50$ values. In addition, the data suggest that clump ejecta initially move along near-radial, bright structures, which then separate into HVECs and larger dust grains that steadily bend backwards relative to the comet's orbital motion due to the effects of solar radiation and gravity. These structures gradually form new striae in the dust tail. The near-periodic spacing of the striae may be indicative of outgassing activity modulation due to the comet nucleus' rotation. It is, however, unclear whether all striae are formed as a result of this process.
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