K2-399 b is not a planet
Astronomy and Astrophysics, vol. 689, pp. L8
Abstract
Context. The transit technique has been very efficient over the past decades in detecting planet-candidate signals. The so-called statistical validation approach has become a popular way of verifying a candidate’s planetary nature. However, the incomplete consideration of false-positive scenarios and data quality can lead to misinterpretation of the results. Aims. In this work, we revise the planetary status of K2-399 b, a validated planet with an estimated false-positive probability of 0.078% located in the middle of the so-called Neptunian desert, and hence a potential key target for atmospheric prospects. Methods. We used radial velocity data from the CARMENES, HARPS, and TRES spectrographs, as well as ground-based multiband transit photometry provided by LCOGT MuSCAT3 and broad band photometry to test the planetary scenario. Results. Our analysis of the available data does not support the existence of this (otherwise key) planet, and instead points to a scenario composed of an early G-dwarf orbited –with a period of a 846.62−0.28+0.22 days– by a pair of eclipsing M-dwarfs (hence a hierarchical eclipsing binary) likely in the mid-type domain. We thus demote K2-399 b as a planet. Conclusions. We conclude that the validation process, while very useful to prioritize follow-up efforts, must always be conducted with careful attention to data quality while ensuring that all possible scenarios have been properly tested to get reliable results. We also encourage developers of validation algorithms to ensure the accuracy of a priori probabilities for different stellar scenarios that can lead to this kind of false validation. We further encourage the use of follow-up observations when possible (such as radial velocity and/or multiband light curves) to confirm the planetary nature of detected transiting signals rather than only relying on validation tools.
Authors 21
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, 541 Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada 542 (Madrid), Spain
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, 544 Cambridge, MA 02138, USA
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, 544 Cambridge, MA 02138, USA
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Affiliation as printed
Center for Exoplanets and Habitability, University of Warwick, Gib-548 bet Hill Road, Coventry, UK
Department of Physics, University of Warwick, Gibbet Hill Road, 546 Coventry, UK
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Affiliation as printed
Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro 550 Giuria, 1, 10125, Torino, Italy
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Affiliation as printed
Dept. of Physics & Astronomy, Swarthmore College, Swarthmore, 552 PA 19081, USA
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, 541 Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada 542 (Madrid), Spain
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, 541 Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada 542 (Madrid), Spain
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Consejo Superior de Investigaciones Científicas · Centro de Astrobiología
Affiliation as printed
Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, 541 Camino Bajo del Castillo s/n, 28692, Villanueva de la Cañada 542 (Madrid), Spain
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Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto
Affiliation as printed
Instituto de Astrofísica e Ciências do Espaço, Universidade do 554 Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
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Affiliation as printed
Centro Astronómico Hispano en Andalucía, Sierra de los Filabres 556 sn, 04550, Gérgal Almería, Spain 557
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, 544 Cambridge, MA 02138, USA
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Astrobiology Center · Instituto de Astrofísica de Canarias · The University of Tokyo
Affiliation as printed
Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tener-562 ife, Spain
Komaba Institute for Science, The University of Tokyo, 3-8-1 558 Komaba, Meguro, Tokyo 153-8902, Japan 559 10 Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 560 561
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Astrobiology Center · Instituto de Astrofísica de Canarias · The University of Tokyo
Affiliation as printed
Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tener-562 ife, Spain
Komaba Institute for Science, The University of Tokyo, 3-8-1 558 Komaba, Meguro, Tokyo 153-8902, Japan 559 10 Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 560 561
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Affiliation as printed
Department of Physics, University of Warwick, Gibbet Hill Road, 546 Coventry, UK
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National Astronomical Observatory of Japan
Affiliation as printed
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mi-566 taka, Tokyo 181-8588, Japan 567
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National Astronomical Observatory of Japan
Affiliation as printed
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mi-566 taka, Tokyo 181-8588, Japan 567
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Leiden University · Leiden Observatory · Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University 568 of Technology, Onsala Space Observatory, 43992, Sweden 569
Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA, 570 Leiden, The Netherlands
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