The SPIRou Legacy Survey

Detection of a nearby world orbiting in the habitable zone of Gl 725B achieved by correcting strong telluric contamination in near-infrared radial velocities with wapiti

¹ Université de Toulouse, UPS-OMP, IRAP, CNRS, 14 avenue E. Belin, Toulouse 31400, France
² SUPA School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ Trottier Institute for Research on Exoplanets, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada
⁵ Observatoire du Mont-Mégantic, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada
⁶ Aix Marseille Univ, CNRS, CNES, Institut Origines, LAM, Marseille, France
⁷ Université Marie et Louis Pasteur, CNRS, Observatoire des Sciences de l’Univers THETA Franche-Comté Bourgogne, Institut UTINAM (UMR 6213), 25000 Besançon, France
⁸ Department of Earth Sciences, University of Hawaii at Manoa, Honolulu, HI 96822, USA
⁹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁰ Department of Physics & Astronomy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada
¹¹ Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹² Canada France Hawaii Telescope (CFHT) Corporation, UAR2208 CNRS-INSU, 65-1238 Mamalahoa Hwy, Kamuela 96743 HI, USA
¹³ Universidade Federal do Rio Grande do Norte (UFRN), Departamento de Física, 59078-970, Natal, RN, Brazil

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 9 May 2025
Accepted: 17 November 2025

Abstract

Context. M dwarfs are prime targets in the search for exoplanets because of their prevalence and because low-mass planets can be better detected with radial velocity (RV) methods. In particular, the near-infrared (NIR) spectral domain offers an increased RV sensitivity and potentially reduced stellar activity signals. Precise NIR RV measurements are strongly affected by telluric absorption lines from the Earth’s atmosphere, however.

Aims. We searched for planets orbiting Gl 725 B, a nearby late-M dwarf located at 3.5 pc, using high-precision SPIRou RV observations. We also assessed the effect of telluric contamination on these measurements and evaluated the performance of the weighted principal component analysis reconstruction (wapiti) method, which is a weighted principal component analysis (wPCA) approach designed to mitigate these systematics and to improve the sensitivity of planet detections.

Methods. Using synthetic and observational SPIRou data, we simulated the effect of telluric lines on RV data under varying barycentric Earth radial velocity (BERV) conditions. We then applied the wapiti method for identifying and correcting telluric-induced systematics in line-by-line RVs. The method was tested through an injection-recovery test on simulated data and was subsequently applied to real SPIRou observations of Gl 725 B.

Results. wapiti successfully corrects telluric contamination in simulated and real datasets. This enhances the detectability and accuracy of planetary signals. In the corrected Gl 725 B dataset, we identified a two-planet system composed of a candidate inner planet (Gl 725 Bb), with periods of 4.765 ± 0.004 days and a semi-amplitude of 1.4 ± 0.3 m s⁻¹, and a confirmed planet Gl 725 Bc, with a period of 37.90 ± 0.17 days and a semi-amplitude of 1.7 ± 0.3 m s⁻¹. Their minimum mass is 1.5 ± 0.4 M_⊕ and of 3.5 ± 0.7 M_⊕, respectively, and the outer planet is located in the habitable zone of its host star. Using a multi-dimensional Gaussian process framework to model and correct for stellar activity, we also recovered a stellar rotation period of 105.1 ± 3.3 days.