Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
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DOI：
10.1086/507630
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发表时间：
2006-08
期刊：
影响因子：
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通讯作者：
O. Guyon;E. Pluzhnik;M. Kuchner;Benoît Collins;S. Ridgway
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文献类型：
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作者：
O. Guyon;E. Pluzhnik;M. Kuchner;Benoît Collins;S. Ridgway
最近已经提出了许多高对比度的冠状图设计。本文综述了它们在太阳系外行星直接成像中的适用性。我们还开发了一个基于线性代数的日冕摄影模型，该模型既可以解释现有日冕摄影的行为，又可以量化基础物理施加的日冕摄影性能限制。我们发现，日冕仪的最大理论吞吐量等于1减去望远镜的无像差非日冕成像PSF。我们描述了如何设计达到这一基本极限的日冕仪，以及在现有最佳日冕仪设计的基础上仍有多少改进的可能。分析模型和现有设计的数值模拟也表明，随着源尺寸的增加，这一理论极限迅速退化：具有最高吞吐量和最小内工作角(IWA)的“最高性能”日冕仪对恒星角直径最敏感。不幸的是，这排除了使用小型IWA(<；λ/d)日冕仪执行地面行星成像任务的可能性。最后，通过一个详细的数值模拟，准确地解释了恒星角大小、黄道光和外黄道光，以量化在可能的真实观测计划中直接成像太阳系外类地行星的日冕仪设计的效率。我们发现，在光子噪声有限的情况下，具有理论上最优日冕仪的4米望远镜能够以每个目标1小时的曝光时间探测到50颗恒星周围的类地行星(假设吞吐量和exozodi水平与我们的太阳系相似)。我们还表明，在这项研究中考虑的理想单色情况下，至少有两种现有的冠状图设计可以接近这一水平的性能。
Many high-contrast coronagraph designs have recently been proposed. In this paper, their suitability for direct imaging of extrasolar terrestrial planets is reviewed. We also develop a linear algebra based model of coronagraphy that can both explain the behavior of existing coronagraphs and quantify the coronagraphic performance limit imposed by fundamental physics. We find that the maximum theoretical throughput of a coronagraph is equal to 1 minus the nonaberrated noncoronagraphic PSF of the telescope. We describe how a coronagraph reaching this fundamental limit may be designed, and how much improvement over the best existing coronagraph design is still possible. Both the analytical model and numerical simulations of existing designs also show that this theoretical limit rapidly degrades as the source size is increased: the "highest performance" coronagraphs, those with the highest throughput and smallest inner working angle (IWA), are the most sensitive to stellar angular diameter. This unfortunately rules out the possibility of using a small IWA (<λ/d) coronagraph for a terrestrial planet imaging mission. Finally, a detailed numerical simulation that accurately accounts for stellar angular size, zodiacal and exozodiacal light is used to quantify the efficiency of coronagraph designs for direct imaging of extrasolar terrestrial planets in a possible real observing program. We find that in the photon noise-limited regime, a 4 m telescope with a theoretically optimal coronagraph is able to detect Earth-like planets around 50 stars with 1 hr exposure time per target (assuming 25% throughput and exozodi levels similar to our solar system). We also show that at least two existing coronagraph design can approach this level of performance in the ideal monochromatic case considered in this study.