ESPRESSO at VLT

On-sky performance and first results^⋆

¹ Département d’Astronomie, Université de Genève, Ch. des Maillettes 51, 1290 Versoix, Switzerland
e-mail: [email protected]
² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
³ Instituto de Astrofisica de Canarias, Via Lactea, 38200 La Laguna, Tenerife, Spain
⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁵ ESO, European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁶ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
⁷ INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
⁸ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁹ Physics Institute of University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
¹⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹¹ Departamento de Física da Faculdade de Ciências da Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
¹² Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹³ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁴ NRCC-HIA, 5071 West Saanich Road Building VIC-10, Victoria, British Columbia V9E 2E, Canada
¹⁵ ESO, European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
¹⁶ Institute for Fundamental Physics of the Universe, IFPU, Via Beirut 2, 34151 Grignano, Trieste, Italy
¹⁷ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁸ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁹ Consejo Superior de Investigaciones Científicas, 28006 Madrid, Spain
²⁰ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia

Received: 30 April 2020
Accepted: 29 September 2020

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.