K2-399 b is not a planet
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
- José Ángel Cabrera (ORCID: https://orcid.org/0000-0001-6380-1030)
- J. Aceituno
- J. Lillo-Box (ORCID: https://orcid.org/0000-0003-3742-1987)
- O. Balsalobre-Ruza (ORCID: https://orcid.org/0000-0002-6712-3035)
- David W. Latham (ORCID: https://orcid.org/0000-0001-9911-7388)
- N. Narita
- O. Barragán
- A.P. Hatzes
- D. Gandolfi
- D. J. Armstrong (ORCID: https://orcid.org/0000-0002-5080-4117)
- T. Hirano
- R.P. Schwarz
- A. Castro-González (ORCID: https://orcid.org/0000-0001-7439-3618)
- K. A. Collins
- N.M. Batalha
- Masayuki Kuzuhara (ORCID: https://orcid.org/0000-0002-4677-9182)
- B. Montesinos (ORCID: https://orcid.org/0000-0002-7982-2095)
- Andreas Hadjigeorghiou (ORCID: https://orcid.org/0000-0003-2222-8746)
- M. Fridlund (ORCID: https://orcid.org/0000-0002-0855-8426)
- A. Fukui
- E.L.N. Jensen
- S. G. Sousa (ORCID: https://orcid.org/0000-0001-9047-2965)
Institutions
- Swarthmore College (US)
- Leiden University (NL)
- University of Warwick (GB)
- Calar Alto Observatory (ES)
- Institute of Astrophysics and Space Sciences (PT)
- Astrobiology Center (JP)
- Center for Astrophysics Harvard & Smithsonian (US)
- Centro de Astrobiología (ES)
- Instituto de Astrofísica de Canarias (ES)
- National Astronomical Observatory of Japan (JP)
- Leiden Observatory
- University of Turin (IT)
- Chalmers University of Technology (SE)
- The University of Tokyo (JP)
Publication Details
- Journal
- Astronomy and Astrophysics
- Published
- 2024-08-26
- DOI
- https://doi.org/10.1051/0004-6361/202451398
- Citations
- 2
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 0.66
Funders
- National Aeronautics and Space Administration
- California Institute of Technology
- UK Research and Innovation
- Ministerio de Ciencia, Innovación y Universidades
- European Commission
- Ministerio de Ciencia e Innovación
- Università degli Studi di Torino
- Science Mission Directorate
- Science and Technology Facilities Council
- Japan Society for the Promotion of Science
- National Institutes of Natural Sciences
- Agencia Estatal de Investigación
- Precursory Research for Embryonic Science and Technology