Night-sky emission correction techniques for high-resolution spectroscopy: Demonstration with NIRPS

Year: 2026

Type: article

Abstract: Context. Ground-based spectrographs operating in the near-infrared (NIR) regime are hampered by various absorption and emission features of Earth’s atmosphere. While considerable attention has been paid to mitigating telluric absorption, correcting telluric emission features remains non-trivial and can significantly affect the observation of faint targets. Aims. We aim to develop and implement automated algorithms for sky background emission correction in the context of high-resolution spectroscopy. These empirical-based algorithms have been officially integrated into both NIRPS data reduction pipelines: NIRPS DRS and APERO DRS. The NIRPS DRS algorithm is additionally functional at the telescope site, enabling quick, real-time telluric-corrected data processing. Designed for flexibility, these techniques can be incorporated into the reduction workflow of any high-resolution spectrograph to improve the radial velocity (RV) performance. Methods. In our approach, a reference sky spectrum is first created by deep-stacking NIRPS sky calibration frames on a common wavelength grid and calculating the weighted median flux per pixel, separately for both the high-accuracy and high-efficiency instrument modes. This process is repeated for all spectral orders and for both the object and sky-calibration fibres: fibre A and fibre B, respectively. In this reference sky spectrum, the sky emission lines can be identified and used to construct a static library. During the data reduction process, the emission features in the library are individually scaled in terms of flux using two distinct techniques, each specific to the two DRS pipelines. Finally, they are locally subtracted from the science observations to minimise their noise contribution to the final spectrum Results. We find that the correction algorithms significantly improve the RV measurements obtained using both the cross-correlation function and line-by-line techniques, enabling NIRPS to achieve submetre-per-second precision in the NIR. The techniques have been successfully validated and demonstrated on both bright (Proxima Centauri) and faint (TOI-406, TOI-3494, TOI-4552) targets, as well as in both high-efficiency and high-accuracy instrument modes. Conclusions. We present the first attempts at empirically subtracting emission line features from high-resolution spectra. These algorithms can be applied independently of the instrumentation and implemented into the data reduction workflow of any high-resolution instrument with minimal modifications required.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202556093

Authors: Avidaan Srivastava, François Bouchy, Xavier Dumusque, Étienne Artigau, René Doyon, Neil J. Cook, Danuta Sosnowska, Flavie Bélanger, David Lafrenière, Frédérique Baron, Lison Malo, Susana C. C. Barros, Björn Benneke, Xavier Bonfils, Marta Bryan, Ryan Cloutier, Nicolas B. Cowan, Elisa Delgado-Mena, Xavier Delfosse, David Ehrenreich, Pedro Figueira, Jonay I. González Hernández, Izan de Castro Leão, Christophe Lovis, Bruno L. Canto Martins, Lucile Mignon, Christoph Mordasini, Francesco Pepe, Rafael Rebolo, Jason Rowe, Nuno C. Santos, Damien Ségransan, Alejandro Suárez Mascareño, Jose Renan De Medeiros, Stéphane Udry, Diana Valencia, Gregg Wade, Romain Allart, Vincent Bourrier, Pedro Branco, Charles Cadieux, Gaspare Lo Curto, Yolanda G. C. Frensch, Jonathan Gagné, Roseane de Lima Gomes, Nicole Gromek, Vigneshwaran Krishnamurthy, Pierrot Lamontagne, Yuri S. Messias, Khaled Al Moulla, Dany Mounzer, Nicola Nari, Léna Parc, Atanas K. Stefanov, Thomas Vandal, Drew Weisserman, Joost P. Wardenier

Language: English

Topic: Astronomy and Astrophysical Research

Subfield: Instrumentation

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,865

Funders: National Science Foundation, Université Laval, “la Caixa” Foundation, Ministère de l'Économie, de l’Innovation et des Exportations du Québec, Ministerio de Ciencia, Innovación y Universidades, European Commission, Agence Nationale de la Recherche, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Université de Montréal, Universidade Federal do Rio Grande do Norte, Instituto de Astrofísica de Canarias, Natural Sciences and Engineering Research Council of Canada, European Research Council, Fundação para a Ciência e a Tecnologia, Fonds de recherche du Québec – Nature et technologies, Agencia Estatal de Investigación, European Social Fund

Awards: G1105844351, G1175115578, G1207375514, G1255325603, G1272900390, G1440137623, G1611901469, G2121614283, G2262748287, G2542020899, G2601397997, G2879720576, G292453335, G300979063, G3161872288, Instituto de Astrofísica e Ciências do Espaço, Instituto de Astrofísica e Ciências do Espaço, G3480869486, G3660205263, G3681454997, G3803561910, G4042783231, G425668148, G4276578120, G464105488, G4728539003, G4761176380, G4821157849, G491712853, G4993383890, G5080475149, G5099673792, G5108148668, G5178665745, G5195188938, G5328565977, G5385376234, G5635532810, G598773271, G6050111196, G6218905885, G654413331, G6731524417, New frontiers in exoplanet characterisation, G6745257626, G6775420319, G6997658380, G7084143925, G7088800351, G7248186603, G7714335329, G7731791180, G7805626310, G7849210366, G7863371703, G7995591378, G8318038168, G8497050386, G8522895693, G863151887, G8888022036, G8964069747, G994248709

OpenAlex ID: W7202172969