arXiv 1503.003142015-03-01astro-ph.SR

日冕物质抛射的偏振三维重建中的非线性

Uncertainties in polarimetric 3D reconstructions of coronal mass ejections

Alessandro Bemporad, Paolo Pagano

发表信息：: A&A 576, A93 (2015)
DOI：: 10.1051/0004-6361/201424390

摘要：

这项工作的目的是量化的三维重建的日冕物质抛射（CME）的位置与偏振比技术获得的不确定性。该方法利用总亮度（tB）和偏振亮度（pB）沿视线（LOS）的不同分布来估计发射等离子体的平均位置。为此，我们假设两个简单的电子密度分布沿LOS（一个恒定的密度和高斯密度分布）的等离子体斑点和合成的预期的tB和pB为不同的距离$z$的斑点从天空的平面（POS）和不同的投影高度$ρ$。因此，沿LOS的斑点的重建位置与真实的比较，允许在该方法中的不确定性的精确确定。独立于分析密度分布，当团块以离POS（即，对于肢体CME）小的距离为中心时，离POS的距离开始被显著高估。偏振比技术提供了我们称之为折叠密度分布的质量质心的LOS位置，通过在POS前面反射和求和位于该平面后面的密度分布的分数来给出。另一方面，当斑点远离POS，但投影高度非常小时（即对于晕CME，$ρ< 1.4$ R $_\odot$），推断的与该平面的距离被显著低估。对于中间位置给出了沿着LOS的真实斑点位置的更好确定，并且特别是当斑点以与POS成$20^\circ$的角度为中心时。这些结果不仅对未来利用偏振比技术进行CME的三维重建具有重要意义，而且对未来旨在为空间天气预报目的提供Halo-CME连续监测的日冕仪的设计也具有重要意义。

英文摘要：

This work is aimed at quantifying the uncertainties in the 3D reconstruction of the location of coronal mass ejections (CMEs) obtained with the polarization ratio technique. The method takes advantage of the different distributions along the line of sight (LOS) of total (tB) and polarized (pB) brightnesses to estimate the average location of the emitting plasma. To this end, we assumed two simple electron density distributions along the LOS (a constant density and Gaussian density profiles) for a plasma blob and synthesized the expected tB and pB for different distances $z$ of the blob from the plane of the sky (POS) and different projected altitudes $ρ$. Reconstructed locations of the blob along the LOS were thus compared with the real ones, allowing a precise determination of uncertainties in the method. Independently of the analytical density profile, when the blob is centered at a small distance from the POS (i.e. for limb CMEs) the distance from the POS starts to be significantly overestimated. Polarization ratio technique provides the LOS position of the center of mass of what we call folded density distribution, given by reflecting and summing in front of the POS the fraction of density profile located behind that plane. On the other hand, when the blob is far from the POS, but with very small projected altitudes (i.e. for halo CMEs, $ρ< 1.4$ R$_\odot$), the inferred distance from that plane is significantly underestimated. Better determination of the real blob position along the LOS is given for intermediate locations, and in particular when the blob is centered at an angle of $20^\circ$ from the POS. These result have important consequences not only for future 3D reconstruction of CMEs with polarization ratio technique, but also for the design of future coronagraphs aimed at providing a continuous monitoring of halo-CMEs for space weather prediction purposes.

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