2015年3月20日日食期间日冕的LOFAR成像
LOFAR imaging of the solar corona during the 2015 March 20 solar eclipse
摘要：
太阳日冕是一种高度结构化的等离子体，其温度可达~2 MK以上。在低频（分米波和米波），电磁波的散射和折射被认为会大大增加成像射电源的大小（高达几弧分）。然而，源的大小与湍流散射的关系仍有待研究。由于在低频率下对日冕进行高空间分辨率观测的罕见性，将源展宽与传播效应联系起来的理论预测尚未得到观测的充分证实。在这里，低频阵列（LOFAR）在2015年3月20日的日偏食期间使用高达~3.5 km（对应于~1- 2 '的分辨率）的基线以120-180 MHz观测日冕。使用了月球反掩星技术，以获得比标准干涉成像（~ 2.4“）更高的空间分辨率（~ 0.6”）。这提供了一种研究散射对表观源尺寸加宽的贡献的方法。有人发现，去掩星技术揭示了一个更结构化的安静的日冕，是没有解决从标准成像，这意味着散射可能被高估，在这个地区时，使用标准成像技术。然而，使用去掩星和标准成像两者，活动区域源被测量为~4'。这可能是由于活跃区域的湍流密度波动增加了无线电波的散射，这比安静的太阳更严重。
英文摘要：
The solar corona is a highly-structured plasma which can reach temperatures of more than ~2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120-180 MHz using baselines of up to ~3.5 km (corresponding to a resolution of ~1-2') during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (~0.6') than that attainable via standard interferometric imaging (~2.4'). This provides a means of studying the contribution of scattering to apparent source size broadening. It was found that the de-occultation technique reveals a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be ~4' using both de-occultation and standard imaging. This may be explained by the increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.
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