Radial velocity homogeneous analysis of M dwarfs observed with HARPS

II. Detection limits and planetary occurrence statistics

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² Observatoire astronomique de l’Université de Genève, 51 chemin Pegasi, 1290 Versoix, Switzerland
³ Departamento de Matemática y Fisica Aplicadas, Universidad Católica de la Santisima Concepción, Alonso de Rivera 2850, Concepción, Chile
⁴ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁵ Instituto de Astrofisica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Departamento de Fisica e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
⁷ CVU – Life in the Universe Center, Geneva, Switzerland
⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

^★ Corresponding author: Lucile.Mignon@univ-grenoble-alpes.fr

Received: 17 June 2024
Accepted: 29 January 2025

Abstract

Aims. We aim to re-determine planetary occurrences around M dwarfs using 20 years of observations from HARPS on 197 targets. The first aim of this study is to propose more precise occurrence rates using the large volume of the sample but also variations to previous calculations, particularly by considering multiplicity, which is now an integral part of planetary occurrence calculations. The second aim is to exploit the extreme longevity of HARPS to determine occurrence rates in the unexplored domain of very long periods.

Methods. This work relied entirely on the 197 radial-velocity time series obtained and analysed in our previous study. By considering they are cleaned of any detectable signal, we convert them into detection limits. We used these 197 limits to produce a detectability map and combined it with confirmed planet detections to establish our occurrence rates. Finally, we converted the detection limits from orbital period to insolation in order to construct an occurrence statistics for the temperate zone.

Results. We find a strong prevalence of low-mass planets around M dwarfs, with an occurrence rate of 120% for planets with a mass between 0.75 and 3 M_⊙. In addition, we compute an occurrence rate of 45.3%${}_{-16}^{+20}$ for temperate-zone planets around M dwarfs. We obtain an occurrence rate of a few percent for giant planets with wide separations. In our sample, these giant planets with wide separations are only detected around the most massive M dwarfs.