Removing systematic effects from astronomical images taken with CCDs requires a detailed understanding of the physics of the imaging process. To aid in this understanding, we have built detailed electrostatic simulations of the LSST CCDs. In order to build an electrostatic model of the LSST CCDs, physical information about the CCDs is required. These details include things such as the physical dimensions of the components of the CCD, dopant profiles, and in some cases, electrical measurements of the CCD. This work documents the results of these physical and electrical measurements on LSST CCDs.
The Brighter-Fatter (hereafter BF) effect in CCD sensors causes increases in the image size of bright objects due to electrostatic repulsion of collected charges. Correcting this effect in the LSST camera is required in order to meet the science goals of the project, especially galaxy shape measurements for weak lensing. The current plan for BF image correction in the LSST is to use the deconvolution method described in Coulton, et.al. [1]. In this work, we study the linearity of the BF effect and effectiveness of the Coulton correction, using both simulation tools and measurements made on pro…
We describe the commissioning of a system which has been built to investigate optimal operation of CCDs for the LSST telescope. The test system is designed for low vibration, high stability operation and is capable of illuminating a detector in flat-field, projected spot, projected pattern and Fe-55 configurations. We compare and describe some considerations when choosing a gain calibration method for CCDs which exhibit the brighter-fatter effect. An optimisation study on a prototype device of gain and full well with varying back substrate bias and gate clock levels is presented.
Intrinsic Pixel Size Variation in an LSST Prototype Sensor
大型综合巡天望远镜（LSST）雄心勃勃的科学目标激发了对LSST相机中新的和意想不到的系统误差源的研究。平场图像是传感器异常的丰富数据来源，尽管这种影响通常在单个平场中被散粒噪声所掩盖。在将许多（$\sim 500$）这样的图像组合成“超平坦”以减少散粒噪声的影响后，我们在逐像素的基础上进行光子传输分析，并在100 ke $^-$及以下的光水平下观察到像素线性或增益中没有空间结构。在125 ke $^-$，柱状结构中观察到的增益图-我们归因于一个通量依赖的电荷转移效率低下。我们还通过分析超平图像中的像素-邻居相关性来探测有效像素大小的小尺度变化，在那里我们观察到$\sim .3\%$水平附近的LSST原型传感器中有效像素大小的内在变化的明确证据。
Spurious shear induced by the tree rings of the LSST CCDs
我们提出了一个分析的影响，在候选传感器的大型综合巡天望远镜（LSST）的星系形状测量的树木年轮。树环是由传感器的硅中的圆形对称杂质梯度引起的横向电场的结果。它们有效地改变了像素区域，并使光生电荷四处移动，从而取代了观察到的光子位置。位移分布产生的扭曲，导致虚假剪切与树轮图案，潜在的偏差宇宙剪切测量。在本文中，我们量化的假剪切的幅度所造成的树木年轮LSST候选传感器，并计算其2点关联函数。我们发现，2点关联函数的虚假剪切相当于一个区域的LSST视场的顺序约为$10^{-13}$，提供了一个可以忽略不计的贡献的2点相关的宇宙剪切信号。其他工作正在进行中，最终结果和分析将在其他地方发表（Okura et al.（2015），in prep.）
The traditional characterization of charge transfer inefficiency (CTI) in charge-coupled devices (CCDs) can suffer from a number of deficiencies: CTI is often only calculated for a limited number of signal levels, CTI is calculated from a limited number of pixels, and the sources of CTI are usually assumed to occur at every pixel-to-pixel transfer. A number of serial CTI effects have been identified during preliminary testing of CCDs developed by Imaging Technology Laboratory (ITL) for use in the Large Synoptic Survey Telescope (LSST) camera focal plane that motivate additional study beyond th…
The LSST focal plane consists of 21 autonomous modules ("Raft Tower Modules", RTM), each of which contains nine thick, fully-depleted 4K x 4K CCDs with associated control and readout electronics. To enable LSST's repetitive short-exposure cadence while maintaining high duty factor and low read noise, the readout is highly parallelized into 3024 independent video channels (16 per CCD, 144 per RTM). Two vendors supplied the LSST sensors; the devices have compatible mechanical and electrical interfaces and meet the same electro-optic specifications, but each RTM is constructed with sensors from a…
The ambitious goals of precision cosmology with wide-field optical surveys such as the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST) demand, as their foundation, precision CCD astronomy. This in turn requires an understanding of previously uncharacterized sources of systematic error in CCD sensors, many of which manifest themselves as static effective variations in pixel area. Such variation renders a critical assumption behind the traditional procedure of flat fielding--that a sensor's pixels comprise a uniform grid--invalid. In this work, we present a method to infe…
The Large Synoptic Survey Telescope (LSST) is a wide-field imaging system of unprecedented etendue. The initial goal of the project is to carry out a ten year imaging survey in six broad passbands (ugrizy) that cover $350 nm < λ< 1.1 μm$. This document reports on the discussions that occurred at workshop (held April 11-12, 2019 at Argonne National Laboratory) that was convened to explore concepts for using the LSST system once the initial survey is complete. Participants discussed the tradeoffs in science performance, cost, and uniqueness for i) imaging surveys using the initial wide-field CCD…
The "dark dips" phenomenon in the LSST Camera on-sky images
Sorbonne Université, Université Paris Cité, CNRS/IN2P3（索邦大学，巴黎西岱大学，法国国家科学研究中心/欧洲核子研究组织）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Physics Department, Brookhaven National Laboratory（布鲁克海文国家实验室物理系）；Physik-Institut, University of Zurich（苏黎世大学物理研究所）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）；National Astronomical Observatory of Japan（日本国立天文台）
Reduction of images and science analysis from ground-based telescopes such as the LSST requires detailed knowledge of the PSF of the image, which includes components attributable to the instrument as well as components attributable to the atmosphere. Because the atmospheric component is constantly changing, the PSF is typically extracted from each image by measuring the size and shape of star images across the CCD, then building a fitting function over the focal plane which is used to model the PSF for analysis of extended sources such as galaxies. Since the stars in each CCD field have a rang…
We describe a system to measure the Quantum Efficiency in the wavelength range of 300 nm to 1100 nm of 40x40 mm n-channel CCD sensors for the construction of the 3.2 gigapixel LSST focal plane. The technique uses a series of instrument to create a very uniform flux of photons of controllable intensity in the wavelength range of interest across the face the sensor. This allows the absolute Quantum Efficiency to be measured with an accuracy in the 7% range. This system will be part of a production facility at Brookhaven National Lab for the basic component of the LSST camera.
The presence of fringing in astronomical CCD images will impact photometric quality and measurements. Yet its impact on the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) has not been fully studied. We present a detailed study on fringing for Charge-Coupled Devices (CCDs) already implemented on the Rubin Observatory LSST Camera's focal plane. After making physical measurements and knowing the compositions, we have developed a model for the e2v CCDs. We present a method to fit for the internal height variation of the epoxy layer within the sensors based on fringing measureme…
We employ electrostatic conversion drift calculations to match CCD pixel signal covariances observed in flat field exposures acquired using candidate sensor devices for the LSST Camera. We thus constrain pixel geometry distortions present at the end of integration, based on signal images recorded. We use available data from several operational voltage parameter settings to validate our understanding. Our primary goal is to optimize flux point-spread function (FPSF) estimation quantitatively, and thereby minimize sensor-induced errors which may limit performance in precision astronomy applicati…
The On-Sky Performance of the LSST Camera CCD Array
University of Zurich（苏黎世大学）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）；National Astronomical Observatory of Japan, Chile Observatory（日本国家天文台智利观测站）；Brookhaven National Laboratory（布鲁克海文国家实验室）；Sorbonne Université, Université Paris Cité（索邦大学，巴黎西岱大学）；Université Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；Harvard University（哈佛大学）；Université Savoie Mont-Blanc（萨瓦蒙布朗大学）；University of California–Santa Cruz（加州大学圣克鲁兹分校）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Aix Marseille Université（艾克斯马赛大学）；Duke University（杜克大学）；Princeton University（普林斯顿大学）；D4D CONSULTING（D4D咨询公司）
