Title: Extreme precision photometry from the ground with beam-shaping diffusers for K2, TESS and beyond Show Chinese title

Title: 从地面使用光束整形扩散器进行K2、TESS及更远的极端精确测光

Abstract: The Transiting Exoplanet Survey Satellite (TESS, launched early 2018) is expected to find a multitude of new transiting planet candidates around the nearest and brightest stars. Timely high-precision follow-up observations from the ground are essential in confirming and further characterizing the planet candidates that TESS will find. However, achieving extreme photometric precisions from the ground is challenging, as ground-based telescopes are subject to numerous deleterious atmospheric effects. Beam-shaping diffusers are emerging as a low-cost technology to achieve hitherto unachievable differential photometric precisions from the ground. These diffusers mold the focal plane image of a star into a broad and stable top-hat shape, minimizing photometric errors due to non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and telescope-induced variable aberrations seen in defocusing. In this paper, we expand on our previous work (Stefansson et al. 2017; Stefansson et al. 2018 [submitted]), providing a further detailed discussion of key guidelines when sizing a diffuser for use on a telescope. Furthermore, we present our open source Python package iDiffuse which can calculate the expected PSF size of a diffuser in a telescope system, along with its expected on-sky diffuser-assisted photometric precision for a host star of a given magnitude. We use iDiffuse to show that most ($\sim$80\%) of the planet hosts that TESS will find will be scintillation limited in transit observations from the ground. Although iDiffuse has primarily been developed to plan challenging transit observations using the diffuser on the ARCTIC imager on the ARC 3.5m Telescope at Apache Point observatory, iDiffuse is modular and can be easily extended to calculate the expected diffuser-assisted photometric precisions on other telescopes. Show Chinese abstract

Abstract: 凌日系外行星勘测卫星（TESS，于2018年初发射）预计将在最近和最明亮的恒星周围发现大量新的凌日行星候选者。 及时的高精度地面后续观测对于确认和进一步表征TESS发现的行星候选者至关重要。 然而，从地面上实现极端的光度精度具有挑战性，因为地面望远镜会受到许多有害的大气效应的影响。 光束整形扩散器正作为一种低成本技术，用于从地面上实现迄今为止无法达到的差分光度精度。 这些扩散器将恒星的焦平面图像塑造成一个宽广且稳定的顶帽形状，从而最小化由于像素响应不均匀、大气视宁度效应、不完善的导星以及聚焦时出现的望远镜引起的可变像差而导致的光度误差。 在本文中，我们扩展了我们之前的工作（Stefansson等，2017；Stefansson等，2018 [待发表]），提供了关于在望远镜上使用扩散器时尺寸设计的关键指南的进一步详细讨论。 此外，我们介绍了我们的开源Python包iDiffuse，它可以计算望远镜系统中扩散器的预期点扩散函数大小，以及给定亮度的主恒星的预期天空中扩散器辅助光度精度。 我们使用iDiffuse表明，TESS将发现的大多数（$\sim$80%）行星宿主在地面上的凌日观测中将受到闪烁限制。 尽管iDiffuse主要是为了在阿波罗点天文台的ARC 3.5米望远镜上的ARCTIC成像仪上使用扩散器进行具有挑战性的凌日观测而开发的，但iDiffuse是模块化的，可以轻松扩展以计算其他望远镜上的预期扩散器辅助光度精度。