Performance of the hybrid externally occulted Lyot solar coronagraph - Application to ASPIICS
Performance of the hybrid externally occulted Lyot solar coronagraph - Application to ASPIICS
复制标题
混合型外隐 Lyot 太阳日冕仪的性能 - 在 ASPIICS 中的应用
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
C. Aime
中科院分区：
文献类型：
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作者：
R. Rougeot;Rémi Flamary;D. Galano;C. Aime
上下文高对比度的混合日冕仪，结合了联合收割机的外部掩蔽和Lyot式日冕仪成为现实，在最近几年，尽管缺乏分析和数值端到端的性能研究。将在欧空局未来的Proba-3编队飞行使命中飞行的太阳日冕仪ASPIICS就是这种混合日冕仪的一个很好的例子。
目标。我们的目标是提供一个数值模型来计算理论性能的混合外掩Lyot式日冕，然后我们的目标是比较的经典Lyot日冕和外掩太阳日冕的性能。我们将提供的水平和强度分布的杂散光，当太阳被认为是一个扩展的来源。我们还研究了不同尺寸的内部遮光器和Lyot停止的效果。
方法.首先，我们已经建立在最近发表的方法，表示从菲涅耳衍射产生的外部遮光器在日冕的入口孔径的衍射波前。其次，我们计算了来自太阳给定点的波前通过仪器的相干传播。这分三个步骤进行：从光圈到外部遮光器的图像，其中设置内部遮光器，从这个平面到入口光圈的图像，其中设置Lyot光阑，并从那里到最终的图像平面。利用轴对称性，我们考虑了来自太阳一个半径的波前，并对强度进行了循环平均。我们的数值计算使用ASPIICS的参数。
结果在ASPIICS的特殊配置中，混合外部遮蔽的Lyot日冕反射10 E-8 Mean Solar Brightness以下的太阳光。Lyot日冕仪有效地补充了外部掩星。我们表明，减少Lyot停止允许一个明确的收益拒绝，甚至比过大的内部掩星，这往往会排除观测非常接近太阳的肢体。作为一个例子，我们提供了一个图表，使我们能够估计性能的内部遮光器和Lyot停止大小的函数。
结论.我们的工作包括一种方法来计算太阳日冕的端到端的性能。
Context. High-contrast hybrid coronagraphs, which combine an external occulter and a Lyot-style coronagraph became a reality in recent years, despite the lack of analytic and numerical end-to-end performance studies. The solar coronagraph ASPIICS which will fly on the future ESA Formation Flying mission Proba-3 is a good example of such a hybrid coronograph.
Aims. We aim to provide a numerical model to compute theoretical performance of the hybrid externally occulted Lyot-style coronagraph, which we then aim to compare to the performance of the classical Lyot coronagraph and the externally occulted solar coronagraph. We will provide the level and intensity distribution of the stray light, when the Sun is considered as an extended source. We also investigate the effect of different sizes for the internal occulter and Lyot stop.
Methods. First, we have built on a recently published approach, to express the diffracted wave front from Fresnel diffraction produced by an external occulter at the entrance aperture of the coronagraph. Second, we computed the coherent propagation of the wave front coming from a given point of the Sun through the instrument. This is performed in three steps: from the aperture to the image of the external occulter, where the internal occulter is set, from this plane to the image of the entrance aperture, where the Lyot stop is set, and from there to the final image plane. Making use of the axis-symmetry, we considered wave fronts originating from one radius of the Sun and we circularly average the intensities. Our numerical computation used the parameters of ASPIICS.
Results. The hybrid externally occulted Lyot coronagraph rejects sunlight below 10E-8Mean Solar Brightness from 1,3 solar radius - in the particular configuration of ASPIICS. The Lyot coronagraph effectively complements the external occultation. We show that reducing the Lyot stop allows a clear gain in rejection, being even better than oversizing the internal occulter, that tends to exclude observations very close to the solar limb. As an illustration, we provide a graph that allows us to estimate performance as a function of the internal occulter and Lyot stop sizes.
Conclusions. Our work consists of a methodological approach to compute the end-to-end performance for solar coronagraph.