Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC 10001893

¹ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
e-mail: silvotti@oato.inaf.it
² Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
³ CNRS, IRAP, 14 Av. E. Belin, 31400 Toulouse, France
⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁵ Département de Physique, Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, Québec H3C 3J7, Canada
⁶ Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
⁷ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁸ Institut d’Astrophysique et de Géophysique, Université de Liège, 17 allée du 6 Août, 4000 Liège, Belgium
⁹ Mt Suhora Observatory, Cracow Pedagogical University, ul. Podchorazych 2, 30-084 Krakow, Poland
¹⁰ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹¹ Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
¹² Observatorio Astronómico Nacional, Universidad Nacional Autónoma de México, BC, 22860, Ensenada, Mexico

Received: 1 July 2014
Accepted: 5 September 2014

Abstract

KIC 10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the Kepler spacecraft in its primary mission. In addition to tens of pulsation frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks at very low frequencies, which is too low to be explained in terms of g modes. The most convincing explanation is that we are seeing the orbital modulation of three Earth-size planets (or planetary remnants) in very tight orbits, which are illuminated by the strong stellar radiation. The orbital periods are P₁ = 5.273, P₂ = 7.807, and P₃ = 19.48 h, and the period ratios P₂/P₁ = 1.481 and P₃/P₂ = 2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of the main pulsation modes of the star at 210.68 μHz corresponds to the third harmonic of the orbital frequency of the inner planet, suggesting that we see, for the first time in an sdB star, g-mode pulsations tidally excited by a planetary companion. The extreme planetary system that emerges from the Kepler data is very similar to the recent discovery of two Earth-size planets orbiting the sdB pulsator KIC 05807616 (Charpinet et al. 2011a).