[论文解读] ESPRESSO at VLT. On-sky performance and first results

F. Pepe, S. Cristiani+98 more|DIGITAL.CSIC (Spanish National Research Council (CSIC))|Oct 1, 2020

Stellar, planetary, and galactic studies参考文献 97被引用 51

一句话总结

ESPRESSO 描述了 VLT 超高分辨光谱仪及其在现场的调试性能和首批保底观测结果，达到高径向速度精度。

ABSTRACT

Context. ESPRESSO is the new high-resolution spectrograph of ESO’s Very Large Telescope (VLT). It was designed for ultra-high radial-velocity (RV) precision and extreme spectral fidelity with the aim of performing exoplanet research and fundamental astrophysical experiments with unprecedented precision and accuracy. It is able to observe with any of the four Unit Telescopes (UTs) of the VLT at a spectral resolving power of 140 000 or 190 000 over the 378.2 to 788.7 nm wavelength range; it can also observe with all four UTs together, turning the VLT into a 16 m diameter equivalent telescope in terms of collecting area while still providing a resolving power of 70 000. Aims. We provide a general description of the ESPRESSO instrument, report on its on-sky performance, and present our Guaranteed Time Observation (GTO) program along with its first results. Methods. ESPRESSO was installed on the Paranal Observatory in fall 2017. Commissioning (on-sky testing) was conducted between December 2017 and September 2018. The instrument saw its official start of operations on October 1, 2018, but improvements to the instrument and recommissioning runs were conducted until July 2019. Results. The measured overall optical throughput of ESPRESSO at 550 nm and a seeing of 0.65″ exceeds the 10% mark under nominal astroclimatic conditions. We demonstrate an RV precision of better than 25 cm s−1 during a single night and 50 cm s−1 over several months. These values being limited by photon noise and stellar jitter shows that the performance is compatible with an instrumental precision of 10 cm s−1. No difference has been measured across the UTs, neither in throughput nor RV precision. Conclusions. The combination of the large collecting telescope area with the efficiency and the exquisite spectral fidelity of ESPRESSO opens a new parameter space in RV measurements, the study of planetary atmospheres, fundamental constants, stellar characterization, and many other fields.

研究动机与目标

• 描述 ESPRESSO 仪器及子系统及其在 VLT 的集成。
• 报道在现场性能和调试进展直至投入运行之初。
• 介绍 Guaranteed-Time Observation (GTO) 计划及初步结果。
• 评估光学透射、径向速度精度和仪器稳定性。
• 讨论对系外行星科学、基本常数与恒星表征的影响。

提出的方法

• 对 ESPRESSO 进行 2017 年至 2019 年的调试和 On-sky 测试以验证性能。
• 光纤供给、交叉分散、高分辨率 echelle 光谱仪设计，供 1-UT 和 4-UT 配置使用。
• 利用第二根光纤进行同时漂移测量以进行波长校准（同时参考模式）。
• 用 ThAr 灯和 Fabry-Pérot 进行波长校准；激光频率梳（LFC）可用但尚未集成。
• 在名义的天文-气候条件下对透射、RV 精度和稳定性进行分析；考虑光子噪声和恒星抖动作为限制因素。
• 解决 1-UT vs 4-UT 的性能差异，并实现 HR42 模式以扩展星等范围。

实验结果

研究问题

• RQ1 ESPRESSO 在名义条件下的现场性能和透射率是多少？
• RQ2 ESPRESSO 能否达到接近或达到 10 cm s−1 的仪器极限径向速度精度，仍存在哪些限制（光子噪声、恒星抖动）？
• RQ3 1-UT 与 4-UT 配置在透射率和 RV 精度方面有何差异？
• RQ4 从 ESPRESSO 的 Guarantee-Time Observations (GTO) 计划可以获得哪些初步科学结果？

主要发现

• 在 550 nm 下， seeing 为 0.65″ 的条件下，整体光学透射率超过 10%！
• 在一个夜晚内的径向速度精度优于 25 cm s−1，且在数月内达到 50 cm s−1。
• 性能受光子噪声和恒星抖动的限制，表明与 10 cm s−1 的仪器精度相容。
• 在单位望远镜之间，在透射率或 RV 精度方面未观测到差异。
• 引入 HR42 模式，将受读出噪声限制的等效星等范围推向更暗的星等。