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arXiv 2009.04820astro-ph.SR
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LASCO-C3日冕光偏振测量24年（1996-2019）--应用于K/F分离和电子密度测定

Coronal Photopolarimetry with the LASCO-C3 Coronagraph over 24 Years [1996-2019] -- Application to the K/F Separation and to the Determination of the Electron Density

Philippe Lamy, Hugo Gilardy, Antoine Llebaria, Eric Quemerais, Fabrice Ernandes

备注：
61 pages, 45 figures. arXiv admin note: text overlap with arXiv:2001.05925
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摘要：

我们提出了一个深入的表征的偏振信道的大角度光谱COronagnetic/LASCO-C3机载SOHO。白光图像的偏振分析利用偏振序列，该偏振序列由通过取向为+60 $^\circ$、0 $^\circ$和-60 $^\circ$的三个偏振器获得的三个图像组成，并由相邻的非偏振图像补充。然而，在1999年发现的0 $^\circ$偏振片的退化迫使我们从之后的其他偏振片重建相应的图像。该分析紧密遵循LASCO-C2开发的方法（Lamy等人，Solar Physics 295，89，2020和arXiv：2001.05925），并实现了Mueller的形式主义，尽管存在额外的困难，特别是杂散光的非轴对称分量的存在。关键修正来自SOHO滚动序列和一致性标准（例如，偏振的切线方向）。在两个完整的太阳活动周23日和24日的外日冕的准不间断的色度学分析成功地实现，我们的最终结果包括其偏振的特性，其偏振辐射，二维电子密度，和K-日冕。C3和C2结果之间的比较，其视野重叠显示出总体一致性。C3的结果进一步与日食和射电测距测量的结果一致，延伸约10个太阳半径，但倾向于进一步发散。虽然日冕的极化到20个太阳半径仍然是高度相关的总磁场的时间变化，这种分歧可能是由于增加极化的F-日冕。

英文摘要：

We present an in-depth characterization of the polarimetric channel of the Large-Angle Spectrometric COronagraph/LASCO-C3 onboard SOHO. The polarimetric analysis of the white-light images makes use of polarized sequences composed of three images obtained through three polarizers oriented at +60$^\circ$, 0$^\circ$, and -60$^\circ$, complemented by a neighboring unpolarized image. However, the degradation of the 0$^\circ$ polarizer noticed in 1999 compelled us to reconstruct the corresponding images from the other ones thereafter. The analysis closely follows the method developed for LASCO-C2 (Lamy, et al. Solar Physics 295, 89, 2020 and arXiv:2001.05925) and implements the formalism of Mueller, albeit with additional difficulties notably the presence of a non-axially symmetric component of stray light. Critical corrections were derived from a SOHO roll sequence and from consistency criteria (e.g., the tangential direction of polarization). The quasi-uninterrupted photopolarimetric analysis of the outer corona over two complete Solar Cycles 23 and 24 was successfully achieved and our final results encompass the characterization of its polarization, of its polarized radiance, of the two-dimensional electron density, and of the K-corona. Comparison between the C3 and C2 results where their field of view overlaps shows an overall agreement. The C3 results are further in agreement with those of eclipses and radio ranging measurements to an elongation of about 10 solar radii but tend to diverge further out. Whereas the coronal polarization out to 20 solar radii is still highly correlated with the temporal variation of the total magnetic field, this divergence probably results from the increasing polarization of the F-corona.

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