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arXiv 2107.04604astro-ph.IMastro-ph.EP
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斑点的神秘生活I.地基日冕仪中剩余大气斑点寿命

The Mysterious Lives Of Speckles. I. Residual atmospheric speckle lifetimes in ground-based coronagraphs

Jared R. Males, Michael P. Fitzgerald, Ruslan Belikov, Olivier Guyon

摘要:

高对比度成像观测从根本上受到称为散斑的空间和时间相关噪声源的限制。斑点噪声的抑制是波前控制和自适应光学(AO)、日冕照相术以及许多后处理技术的关键目标。散斑的平均速率由统计散斑寿命决定,长时间曝光中的散斑限制积分时间与此寿命成正比。随着日冕物质抛射后波前控制技术的不断进步,大气散斑将成为高对比度成像中的限制性噪声源,因此全面了解其统计行为对于优化高对比度成像仪器至关重要。在这里,我们提出了一种新的功率谱密度(PSD)的方法来计算寿命,并开发了一个半解析的方法来预测强度PSD背后的日冕。考虑冻结流湍流模型,分析了类MagAO-X自适应光学系统和25 - 39 m巨型分块镜望远镜(GSMT)尺度系统中的大气剩余散斑寿命。我们发现,标准AO控制将大气散斑寿命从~130 ms缩短到~50 ms,预测控制将进一步缩短寿命到~20 ms。我们发现,散斑寿命随直径,风速,看到,和AO控制区域内的位置。在明亮的恒星的寿命保持在一个粗略的范围内~20毫秒至~100毫秒。由于控制系统的动力学有没有简单的标度律,适用于广泛的系统特性。最后,我们用这些结果来论证,基于遥测的后处理应该使地面望远镜在高对比度成像中达到光子噪声极限。

英文摘要:

High-contrast imaging observations are fundamentally limited by the spatially and temporally correlated noise source called speckles. Suppression of speckle noise is the key goal of wavefront control and adaptive optics (AO), coronagraphy, and a host of post-processing techniques. Speckles average at a rate set by the statistical speckle lifetime, and speckle-limited integration time in long exposures is directly proportional to this lifetime. As progress continues in post-coronagraph wavefront control, residual atmospheric speckles will become the limiting noise source in high-contrast imaging, so a complete understanding of their statistical behavior is crucial to optimizing high-contrast imaging instruments. Here we present a novel power spectral density (PSD) method for calculating the lifetime, and develop a semi-analytic method for predicting intensity PSDs behind a coronagraph. Considering a frozen-flow turbulence model, we analyze the residual atmosphere speckle lifetimes in a MagAO-X-like AO system as well as 25--39 m giant segmented mirror telescope (GSMT) scale systems. We find that standard AO control shortens atmospheric speckle lifetime from ~130 ms to ~50 ms, and predictive control will further shorten the lifetime to ~20 ms on 6.5 m MagAO-X. We find that speckle lifetimes vary with diameter, wind speed, seeing, and location within the AO control region. On bright stars lifetimes remain within a rough range of ~20 ms to ~100 ms. Due to control system dynamics there are no simple scaling laws which apply across a wide range of system characteristics. Finally, we use these results to argue that telemetry-based post-processing should enable ground-based telescopes to achieve the photon-noise limit in high-contrast imaging.

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