NIRPS joining HARPS at ESO 3.6 m

On-sky performance and science objectives

¹ Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
² Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal, Montréal, Québec, Canada
³ Observatoire du Mont-Mégantic, Québec, Canada
⁴ European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁵ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁶ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, RN 59072-970, Brazil
⁷ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁹ Consejo Superior de Investigaciones Científicas (CSIC), 28006 Madrid, Spain
¹⁰ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹¹ Departamento de Física e Astronomia, Faculdade de Ciências, Uni-versidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹² Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON, Canada
¹³ European Southern Observatory (ESO), Av. Alonso de Cordova 3107, Casilla 19001, Santiago de Chile, Chile
¹⁴ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
¹⁵ Centre of Optics, Photonics and Lasers, Université Laval, Québec, Canada
¹⁶ Herzberg Astronomy and Astrophysics Research Centre, National Research Council of Canada, Canada
¹⁷ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciên-cias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
¹⁸ Departamento de Física da Faculdade de Ciências da Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
¹⁹ Space Research and Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²⁰ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
²¹ Department of Physics, University of Toronto, Toronto, ON M5S 3H4, Canada
²² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
²³ Department of Physics & Astronomy, McMaster University, 1280 Main St W, Hamilton, ON, L8S 4L8, Canada
²⁴ Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada
²⁵ Department of Earth & Planetary Sciences, McGill University, 3450 rue University, Montréal, QC H3A 0E8, Canada
²⁶ Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, Fortaleza, Brazil
²⁷ Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada (Madrid), Spain
²⁸ Centre Vie dans l’Univers, Faculté des sciences de l’Université de Genève, Quai Ernest-Ansermet 30, 1205 Geneva, Switzerland
²⁹ Planétarium de Montréal, Espace pour la Vie, 4801 av. Pierre-de Coubertin, Montréal, Québec, Canada
³⁰ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
³¹ York University, 4700 Keele St, North York, ON M3J 1P3, UK
³² University of British Columbia, 2329 West Mall, Vancouver, BC V6T 1Z4, Canada
³³ Western University, Department of Physics & Astronomy and Institute for Earth and Space Exploration, 1151 Richmond Street, London ON N6A 3K7, Canada
³⁴ Light Bridges S.L., Observatorio del Teide, Carretera del Observatorio, s/n Guimar, 38500, Tenerife, Canarias, Spain
³⁵ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
³⁶ Subaru Telescope, National Astronomical Observatory of Japan (NAOJ), 650 N Aohoku Place, Hilo, HI 96720, USA
³⁷ Department of Astronomy & Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
³⁸ Bishop’s Univeristy, Dept of Physics and Astronomy, Johnson-104E, 2600 College Street, Sherbrooke, QC J1M 1Z7, Canada
³⁹ Laboratoire Lagrange, Observatoire de la Côte d’Azur, CNRS, Université Côte d’Azur, Nice, France

^★ Corresponding author: Francois.Bouchy@unige.ch

Received: 7 December 2024
Accepted: 4 June 2025

Abstract

Context. The Near-InfraRed Planet Searcher (NIRPS) is a high-resolution, high-stability near-infrared (NIR) spectrograph equipped with an adaptive optics (AO) system. Installed on the ESO 3.6-m telescope at La Silla Observatory, Chile, it was developed to enable radial velocity (RV) measurements of low-mass exoplanets around M dwarfs and to characterise exoplanet atmospheres in the NIR.

Aims. This paper provides a comprehensive design overview and characterisation of the NIRPS instrument, reporting on its on-sky performance, advising on how to carry out observations, and presenting its guaranteed time observation (GTO) programme.

Methods. Intensive on-sky testing phases were conducted between November 2019 and March 2023. The instrument started its operations on 1 April 2023.

Results. The spectral range continuously covers the Y, J, and H bands from 972.4 to 1919.6 nm. The thermal control system maintains 1 mK stability over several months, thereby minimising drift. The NIRPS’s AO-assisted fibre link improves coupling efficiency and offers a unique high-angular resolution capability with a fibre acceptance of only 0.4″. A high spectral resolving power of R ~ 90 000 and R ~ 75 000 is provided in high-accuracy (HA) and high-efficiency (HE) modes, respectively. The overall throughput from the top of the atmosphere to the detector peaks at 13%. The RV precision, measured on the bright star Proxima with a known exoplanetary system, is 77 cms⁻¹. NIRPS and HARPS can be used simultaneously, offering unprecedented spectral coverage for spectroscopic characterisation and stellar activity mitigation. Modal noise can be aptly mitigated by the implementation of fibre stretchers and AO scanning mode.

Conclusions. Initial results confirm that NIRPS opens new possibilities for RV measurements, stellar characterisation, and exoplanet atmosphere studies with high precision and high spectral fidelity. NIRPS demonstrated stable RV precision at the level of 1 m s⁻¹ over several weeks. The instrument’s high throughput, particularly in the H band, offers a notable improvement over previous spectrographs, enhancing our ability to detect small exoplanets.