Publication: The CARMENES search for exoplanets around M dwarfs Planet occurrence rates from a subsample of 71 stars
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2021-09-17
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Abstract
Context. The CARMENES exoplanet survey of M dwarfs has obtained more than 18 000 spectra of 329 nearby M dwarfs over the past five years as part of its guaranteed time observations (GTO) program. Aims. We determine planet occurrence rates with the 71 stars from the GTO program for which we have more than 50 observations.
Methods. We use injection-and-retrieval experiments on the radial-velocity (RV) time series to measure detection probabilities. We include 27 planets in 21 planetary systems in our analysis.
Results. We find 0.06^(+0.04)_(−0.03) giant planets (100 Mꙩ < M_(pl) sin i < 1000 Mꚛ) per star in periods of up to 1000 d, but due to a selection bias this number could be up to a factor of five lower in the whole 329-star sample. The upper limit for hot Jupiters (orbital period of less than 10 d) is 0.03 planets per star, while the occurrence rate of planets with intermediate masses (10 Mꚛ < M_(pl) sin i < 100 Mꚛ) is 0.18+0.07 −0.05 planets per star. Less massive planets with 1 Mꚛ < M_(pl) sin i < 10 Mꚛ are very abundant, with an estimated rate of 1.32+0.33 −0.31 planets per star for periods of up to 100 d. When considering only late M dwarfs with masses M. < 0.34 Mꚛ, planets more massive than 10 Mꚛ become rare. Instead, low-mass planets with periods shorter than 10 d are significantly overabundant.
Conclusions. For orbital periods shorter than 100 d, our results confirm the known stellar mass dependences from the Kepler survey: M dwarfs host fewer giant planets and at least two times more planets with M_(pl) sin i < 10 Mꚛ than G-type stars. In contrast to previous results, planets around our sample of very low-mass stars have a higher occurrence rate in short-period orbits of less than 10 d. Our results demonstrate the need to take into account host star masses in planet formation models.
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© ESO 2021. Artículo firmado por 28 autores. We thank the anonymous referee for many useful comments and suggestions that helped improving our paper. We thank M. Esposito for the explanation of his detection limit method and V. Wolthoff for useful insights in occurrence rate retrieval methods. This work was supported by the Thüringer Ministerium für Wirtschaft, Wissenschaft und Digitale Gesellschaft, and the Deutsche Forschungsgemeinschaft (DFG) under the DFG Research Unit FOR2544 “Blue Planets around Red Stars” (RE 2694/8-1) and the project GU 464/20-1. CARMENES is an instrument at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto (Almería, Spain), operated jointly by the Junta de Andalucía and the Instituto de Astrofísica de Andalucía (CSIC). CARMENES was funded by the MaxPlanck-Gesellschaft (MPG), the Consejo Superior de Investigaciones Científicas (CSIC), the Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. We acknowledge financial support from the Agencia Estatal de Investigación of the Ministerio de Ciencia, Innovación y Universidades and the ERDF through projects PID2019-109522GBC5[1:4]/AEI/10.13039/501100011033 and the Centre of Excellence “Severo Ochoa” and “María de Maeztu” awards to the Instituto de Astrofísica de Canarias (SEV-2015-0548), Instituto de Astrofísica de Andalucía (SEV-2017- 0709), and Centro de Astrobiología (MDM-2017-0737), the Generalitat de Catalunya/CERCA programme, the DFG program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (JE 701/5-1), and NASA (NNX17AG24G).