[论文解读] Survey Operations for the Dark Energy Spectroscopic Instrument

E. F. Schlafly, D. Kirkby+48 more|arXiv (Cornell University)|Jun 9, 2023

Astronomy and Astrophysical Research参考文献 6被引用 13

一句话总结

该论文描述 DESI 的夜间观测运行，包括计划、场区选择、实时评估、数据缩减、质量控制以及合并目标列表更新，并将前 1.1 年的观测表现与模拟进行比较。

ABSTRACT

The Dark Energy Spectroscopic Instrument (DESI) survey is a spectroscopic survey of tens of millions of galaxies at $0 < z < 3.5$ covering 14,000 square degrees of the sky. In its first 1.1 years of survey operations, it has observed more than 14 million galaxies and 4 million stars. We describe the processes that govern DESI's observations of the 15,000 fields composing the survey. This includes the planning of each night's observations in the afternoon; automatic selection of fields to observe during the night; real-time assessment of field completeness on the basis of observing conditions during each exposure; reduction, redshifting, and quality assurance of each field of targets in the morning following observation; and updates to the list of future targets to observe on the basis of these results. We also compare the performance of the survey with historical expectations and find good agreement. Simulations of the weather and of DESI observations using the real field-selection algorithm show good agreement with the actual observations. After accounting for major unplanned shutdowns, the dark time survey is progressing about 7% faster than forecast, which is good agreement given approximations made in the simulations.

研究动机与目标

• 解释在主要调查（2021–2022）期间支配 DESI 观测的运营工作流程。
• 描述夜间计划、场区选择与实时评估如何优化望远镜观测时间。
• 详细说明 DESI 使用的数据处理、质量保证以及目标目录的更新。
• 评估 DESI 的性能与历史期望和模拟的比较。
• 强调合并目标清单和调查设计如何实现可重复性和预测性。

提出的方法

• 概述与运作相关的 DESI 仪器与调查策略（tiles、dark/bright/backup 计划）。
• 解释用于安排观测的 airmass 优化和 slew 优化算法。
• 描述从计划到 MTL 更新的日常运行步骤（包括 ETC 和流水线数据缩减）。
• 定义有效时间以及在不同条件下深度目标如何转化为曝光需求。
• 提出一个框架，通过设计场区选择算法对调查进行仿真并与实际观测进行比较。

Figure 1: Survey completeness on 2022–06–14, in the dark (top) and bright (bottom) programs. Green areas are completely finished, while white areas are unfinished. Areas not included in the footprint are in gray. Regions with $E(B-V)>0.3$ are outlined by the solid contours. The dotted and dashed lin

实验结果

研究问题

• RQ1 在深度优先约束下，DESI 的夜间场区选择和 tiles 调度如何实现以最大化调查效率？
• RQ2 曝光目标和有效时间如何驱动暗/明/备份计划中的观测策略？
• RQ3 仿真在多大程度上再现了 DESI 在前 1.1 年的实际调查性能？
• RQ4 合并目标清单在维持可重复性和指导观测更新方面的作用是什么？
• RQ5 airmass、 extinction 和天空条件如何影响计划与实际观测日程？

主要发现

• 在前 1.1 年的运行中，DESI 观测了超过 1400 万个星系和 400 万个恒星。
• 使用真实场区选择算法的仿真与实际观测结果显示良好一致。
• 在考虑重大计划外停机后，暗时段调查的进展约比预测快 7%。
• 观测系统利用 seeing、透明度和天空亮度测量实现实时曝光长度调整，以获得均一的光谱质量。
• 合并目标清单与相互依赖的场观测流程确保在观测新 tiles 之前解决待观测任务。
• 大约 5.2 的暗场 tile 覆盖率和 3.2 的亮场 tile 覆盖率来自七次暗场和四次亮场观测。

Figure 2: The fraction of the sky that is covered by a given number of tiles in the seven-pass dark tiling and the four-pass bright tiling. On average, a given part of the sky is covered by 5.2 dark tiles and 3.2 bright tiles.