Letter to the Editor

The SOPHIE search for northern extrasolar planets

XVI. HD 158259: A compact planetary system in a near-3:2 mean motion resonance chain

¹ Observatoire Astronomique de l’Université de Genéve, 51 Chemin des Maillettes, 1290 Versoix, Switzerland
e-mail: nathan.hara@unige.ch
² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
³ Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209, USA
⁴ Observatoire de Haute-Provence, CNRS, Aix Marseille Universitté, Institut Pythtéas UMS 3470, 04870 Saint-Michel-l’Observatoire, France
⁵ Departamento de Matemática y Física Aplicadas, Universidad Católica de la Santísima Concepción, Alonso de Rivera 2850, Concepción, Chile
⁶ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁷ Institut d’Astrophysique de Paris, UMR7095 CNRS, Universitté Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁸ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁹ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
¹⁰ CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina
¹¹ Instituto de Astrofésica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, Santiago, Chile
¹² Millennium Institute for Astrophysics, Macul, Chile
¹³ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA
¹⁴ Departamento de Fésica e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
¹⁶ Centre for Exoplanets and Habitability, University of Warwick, Coventry CV4 7AL, UK

Received: 4 December 2019
Accepted: 10 March 2020

Abstract

Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline.

Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ₁ periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique.

Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M_⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R_⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M_⊕ mass estimate.

Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances.