Clues to cometary circular polarization from studying the magnetic field in the vicinity of the nucleus of comet 67P/Churyumov-Gerasimenko
Clues to cometary circular polarization from studying the magnetic field in the vicinity of the nucleus of comet 67P/Churyumov-Gerasimenko
复制标题
通过研究 67P/Churyumov-Gerasimenko 彗核附近的磁场来了解彗星圆偏振的线索
DOI：
10.1093/mnras/stw2843
复制
发表时间：
2016
影响因子：
4.8
通讯作者：
A. Lazarian
中科院分区：
文献类型：
--
作者：
L. Kolokolova;C. Koenders;C. Goetz;V. Rosenbush;N. Kiselev;Thiem C. Hoang;A. Lazarian
彗星连续谱带中的圆偏振现象已被观测了 30 多年。最近，使用6米大望远镜Alt-azimuthal（BTA）望远镜（俄罗斯）获得了10多颗彗星的圆偏振成像数据。然而，尽管积累了大量数据，彗星环境中形成圆偏振的机制仍然是个谜。常规机制，例如光学厚介质中的多重散射或特定镜面不对称性（包括同手性）的粒子或材料的支配，无法解释这些观察结果。粒子排列被认为是最可行的机制；然而，颗粒排列的原因尚不清楚。最合理的机制，即磁场中的排列，被认为是值得怀疑的，因为彗星没有自己的磁场，而且根据哈雷彗星的现场结果，太阳磁场无法深入穿透彗发。然而，彗星彗发与太阳磁场相互作用的新理论研究，特别是罗塞塔对67P/Churyumov-Gerasimenko彗星反磁性空腔的观测表明，太阳风磁场可以穿透到距核数十公里的地方。这使我们能够建议太阳磁场的排列是观察到圆偏振的原因。根据67P彗星获得的数据，我们估计了彗星粒子在太阳磁场中排列所需的时间。获得的估计与彗星圆偏振的观测结果一致。
Circular polarization in cometary continuum bands has been observed for more than 30 years. Recently, imaging data on circular polarization have been obtained for more than 10 comets using the 6-m Big Telescope Alt-azimuthal (BTA) telescope (Russia). However, despite the accumulation of significant amounts of data, the mechanisms that form circular polarization in the cometary environment are still a mystery. Regular mechanisms, such as multiple scattering in an optically thick medium or the domination of particles or materials of a specific mirror asymmetry (including homochirality), could not explain the observations. Particle alignment was considered the most feasible mechanism; however, the cause of the particle alignment was not clear. The most reasonable mechanism, alignment in a magnetic field, was considered doubtful, as comets do not have their own magnetic field and, according to the in situ results for comet Halley, the solar magnetic field could not penetrate deeply into the coma. However, new theoretical studies of cometary coma interaction with the solar magnetic field and, especially,Rosettaobservations of the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko showed that the solar wind magnetic field can penetrate as close to the nucleus as several dozen kilometres. This allows us to suggest alignment in the solar magnetic field as a reason for the observed circular polarization. Based on the data obtained for comet 67P, we estimate the time necessary for the alignment of cometary particles in the solar magnetic field. The estimates obtained are consistent with the observations of cometary circular polarization.