利用RoboPol观测北极星耀斑的光学偏振图
Optical polarization map of the Polaris Flare with RoboPol
摘要：
在分子云中恒星形成之前的阶段还知之甚少。通过研究静止云的性质，如其磁场结构，可以获得一些见解。光场的天平面取向可以通过偏振光来追踪。我们提出了第一个扩展的，宽视场（$\sim$ 10 $\rm deg^2$）地图的北极星耀斑云的尘埃吸收诱导的光学偏振的背景恒星，使用RoboPol偏振仪在Skinakas天文台。这是RoboPol宽视场成像能力的首次应用。在R波段采集数据，并使用仪器的自动还原管道进行分析。我们详细介绍了针对宽场观测的减少管道中的优化。我们的分析导致了641颗恒星的可靠测量，中值分数线性偏振为1.3%。投影磁场显示出大尺度的有序图案。在高纬度，它似乎与赫歇尔-SPIRE尘埃排放图（250 $μm$）中看到的微弱条纹对齐，而在中心4-5度的$^2$中，它显示出漩涡状特征。我们得到的整体偏振模式是在很好的协议与大规模测量普朗克尘埃发射偏振在同一地区的天空。
英文摘要：
The stages before the formation of stars in molecular clouds are poorly understood. Insights can be gained by studying the properties of quiescent clouds, such as their magnetic field structure. The plane-of-the-sky orientation of the field can be traced by polarized starlight. We present the first extended, wide-field ($\sim$10 $\rm deg^2$) map of the Polaris Flare cloud in dust-absorption induced optical polarization of background stars, using the RoboPol polarimeter at the Skinakas Observatory. This is the first application of the wide-field imaging capabilities of RoboPol. The data were taken in the R-band and analysed with the automated reduction pipeline of the instrument. We present in detail optimizations in the reduction pipeline specific to wide-field observations. Our analysis resulted in reliable measurements of 641 stars with median fractional linear polarization 1.3%. The projected magnetic field shows a large scale ordered pattern. At high longitudes it appears to align with faint striations seen in the Herschel-SPIRE map of dust emission (250 $μm$), while in the central 4-5 deg$^2$ it shows an eddy-like feature. The overall polarization pattern we obtain is in good agreement with large scale measurements by Planck of the dust emission polarization in the same area of the sky.
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