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arXiv 2011.04674astro-ph.IM
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视限成像巡天-小型与大型望远镜

Seeing-limited imaging sky surveys -- small vs. large telescopes

Eran O. Ofek, Sagi Ben-Ami

摘要:

通常,大型望远镜的建造和运营成本比其收集面积增长得更快。这减缓了科学进步,使得增加望远镜尺寸变得昂贵和复杂。代表成像巡天望远镜能力并捕捉广泛科学目标的一个度量标准是望远镜抓取-单位时间内可探测到标准烛光的空间体积。我们提供了一个解析表达式的把握,也表明,在背景占主导地位的噪声限制,最佳曝光时间是死时间的三倍。我们引入了一个相关的度量,我们称之为信息内容的把握,它总结了单位时间内望远镜观察到的所有源的方差。对于以观测为主的巡天,在抓地力、光学扩展量或收集区域优化方面,最近的技术进步使得建造多个小型望远镜比建造具有类似抓地力或光学扩展量的单个大型望远镜更具成本效益。在这些关键的进步中,有一个是具有小于4微米像素的大尺寸背照式CMOS探测器的可用性,它非常适合在小型快速望远镜的典型焦距下对标准视宁条件进行采样。我们还讨论了可能使用多个小望远镜光谱。我们认为,如果使用多个小型望远镜实现具有成本效益的宽视场成像和多目标光谱仪的所有障碍都被消除,那么建造新的单一大孔径(> 1米)可见光望远镜的动机将被削弱。这些想法导致了目前正在建造的大阵列巡天望远镜(LAST)的概念。

英文摘要:

(Abridged) Typically large telescope construction and operation costs scale up faster than their collecting area. This slows scientific progress, making it expensive and complicated to increase telescope size. A metric that represents the capability of an imaging survey telescopes, and that captures a wide range of science objectives, is the telescope grasp -- the amount of volume of space in which a standard candle is detectable per unit time. We provide an analytic expression for the grasp, and also show that in the background-dominated noise limit, the optimal exposure time is three times the dead time. We introduce a related metric we call the information-content grasp, which summarizes the variance of all sources observed by the telescope per unit time. For seeing-dominated sky surveys, in terms of grasp, etendue, or collecting-area optimization, recent technological advancements make it more cost effective to construct multiple small telescopes rather than a single large telescope with a similar grasp or etendue. Among these key advancements are the availability of large-format back-side illuminated CMOS detectors with <4 micron pixels, well suited to sample standard seeing conditions given typical focal lengths of small fast telescopes. We also discuss the possible use of multiple small telescopes for spectroscopy. We argue that if all the obstacles to implementing cost-effective wide-field imaging and multi-object spectrographs using multiple small telescopes are removed, then the motivation to build new single large-aperture (>1m) visible-light telescopes which are seeing-dominated, will be weakened. These ideas have led to the concept of the, currently under construction, Large-Array Survey Telescope (LAST).

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