A High-precision Technique to Correct for Residual Atmospheric Dispersion in High-contrast Imaging Systems
A High-precision Technique to Correct for Residual Atmospheric Dispersion in High-contrast Imaging Systems
复制标题
校正高对比度成像系统中残余大气色散的高精度技术
DOI：
10.1088/1538-3873/128/970/124404
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
N.
中科院分区：
文献类型：
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作者：
Pathak;P.; Guyon;O.; Jovanovic;N.; Lozi;J.; Martinache;F.; Minowa;Y.; Kudo;T.; Takami;H.; Hayano;Y.; Narita;N.
系外行星的直接探测和光谱学需要高对比度成像。特别是对于可居住的系外行星，位于与主恒星的小角度距离，使用小内工作角（IWA）日冕仪有效地抑制星光是至关重要的。反过来，这些日冕仪需要仔细控制直接影响其性能的波前。对于地面望远镜来说，大气折射也是一个重要的因素，因为它会导致点扩散函数（PSF）的模糊，而日冕仪再也无法有效地抑制这种模糊。传统上，大气折射是由大气色散补偿器（ADC）补偿的。ADC控制依赖于大气的先验模型，该模型的参数完全基于望远镜的指向，这可能导致补偿不完全。对于像斯巴鲁日冕极端自适应光学（SCExAO）系统这样的高对比度仪器，它采用了非常小的IWA日冕仪，为了获得最佳性能，PSF在科学波段的折射引起的涂抹必须小于1 mas。在本文中，我们提出了第一次对残余大气色散的天空测量和校正。大气色散是直接从科学图像中测量的，使用人工引入的自适应斑点网格作为诊断反馈到望远镜的ADC。使用我们目前的设置，我们能够将宽带光（y-到h波段）的初始残余大气色散从18.8 mas减少到4.2 mas，仅在h波段减少到1.4 mas。这项工作与即将到来的超大型望远镜（elt）特别相关，这将需要对其ADC进行精细控制，以充分发挥其高对比度成像潜力。
Direct detection and spectroscopy of exoplanets requires high-contrast imaging. For habitable exoplanets in particular, located at a small angular separation from the host star, it is crucial to employ small inner working angle (IWA) coronagraphs that efficiently suppress starlight. These coronagraphs, in turn, require careful control of the wavefront that directly impacts their performance. For ground-based telescopes, atmospheric refraction is also an important factor, since it results in a smearing of the point-spread function (PSF), that can no longer be efficiently suppressed by the coronagraph. Traditionally, atmospheric refraction is compensated for by an atmospheric dispersion compensator (ADC). ADC control relies on an a priori model of the atmosphere whose parameters are solely based on the pointing of the telescope, which can result in imperfect compensation. For a high-contrast instrument like the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, which employs very small IWA coronagraphs, refraction-induced smearing of the PSF has to be less than 1 mas in the science band for optimum performance. In this paper, we present the first on-sky measurement and correction of residual atmospheric dispersion. Atmospheric dispersion is measured from the science image directly, using an adaptive grid of artificially introduced speckles as a diagnostic to feedback to the telescope's ADC. With our current setup, we were able to reduce the initial residual atmospheric dispersion from 18.8 mas to 4.2 in broadband light (y-to H-band) and to 1.4 mas in the H-band only. This work is particularly relevant to the upcoming extremely large telescopes (ELTs) that will require fine control of their ADC to reach their full high-contrast imaging potential.