NIRPS joining HARPS at ESO 3.6 m. On-sky performance and science objectives

TL;DR

NIRPS is a high-resolution near-infrared spectrograph with AO on the ESO 3.6-m telescope, enabling precise exoplanet RV measurements and atmospheric characterization, demonstrating stable performance and high throughput since April 2023.

Contribution

This paper presents the comprehensive design, on-sky performance, and initial scientific capabilities of NIRPS, a new high-resolution NIR spectrograph integrated with AO for exoplanet research.

Findings

Achieved RV precision of 77 cm/s on Proxima Centauri.

Demonstrated stable RV measurements at 1 m/s over weeks.

High throughput of up to 13% enhances exoplanet detection capabilities.

Abstract

The Near-InfraRed Planet Searcher (NIRPS) is a high-resolution, high-stability near-infrared (NIR) spectrograph equipped with an AO system. Installed on the ESO 3.6-m telescope, it was developed to enable radial velocity (RV) measurements of low-mass exoplanets around M dwarfs and to characterise exoplanet atmospheres in the NIR. This paper provides a comprehensive design overview and characterisation of the NIRPS instrument, reporting on its on-sky performance, and presenting its GTO programme. The instrument started its operations on 1 Apr 2023 after intensive on-sky testing phases. 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. The NIRPS AO-assisted fibre link improves coupling efficiency and offers a unique high-angular resolution capability with a fibre acceptance of only 0.4 arcsec. A high spectral resolving power of 90 000 and 75 000 is provided in HA and HE modes, respectively. The overall throughput from the top of the atmosphere to the detector peaks at 13 percent. The RV precision, measured on the bright star Proxima with a known exoplanetary system, is 77 cm/s. 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. 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 over several weeks. The instrument high throughput offers a notable improvement over previous spectrographs, enhancing our ability to detect small exoplanets.