Disproving the validated planets K2-78b, K2-82b, and K2-92b

The importance of independently confirming planetary candidates

¹ Deutsches Zentrum für Luft- und Raumfahrt, Rutherfordstr. 2, 12489 Berlin, Germany
e-mail: juan.cabrera@dlr.de
² Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
³ University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, UK
⁴ Instituto de Astrofísica de Canarias, vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁶ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁷ Observatoire de Genève, Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland
⁸ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁹ Aix Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, UMR 7326 Marseille, France
¹⁰ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, 2160 Buenos Aires, Argentina
¹¹ CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), 430 Buenos Aires, Argentina
¹² Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
¹³ Department of Astronomy and Astrophysics, Berlin University of Technology, 10623 Berlin, Germany
¹⁴ Department of Geosciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, 6997801 Tel Aviv, Israel

Received: 24 May 2017
Accepted: 26 July 2017

Abstract

Context. Transiting super-Earths orbiting bright stars in short orbital periods are interesting targets for the study of planetary atmospheres.

Aims. While selecting super-Earths suitable for further characterisation from the ground from a list of confirmed and validated exoplanets detected by K2, we found some suspicious cases that led to us reassess the nature of the detected transiting signal.

Methods. We performed a photometric analysis of the K2 light curves and centroid motions of the photometric barycenters.

Results. Our study shows that the validated planets K2-78b, K2-82b, and K2-92b are not planets, but background eclipsing binaries. The eclipsing binaries are inside the Kepler photometric aperture, but outside the ground-based high-resolution images that were used for validation.

Conclusions. We advise extreme care in the validation of candidate planets that are discovered by space missions. It is important that all the assumptions in the validation process are carefully checked. An independent confirmation is mandatory in order to avoid wasting valuable resources on further characterisation of non-existent targets.