An ultra-short period rocky super-Earth orbiting the G2-star HD 80653^★,★★

¹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
e-mail: giuseppe.frustagli@inaf.it
² Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
³ Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
⁴ Department of Physics, Harvard University, 17 Oxford Street, Cambridge MA 02138, USA
⁵ Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 01238, USA
⁶ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁷ Astrophysics Group, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
⁸ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
⁹ DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 328, 2800 Kgs. Lyngby, Denmark
¹⁰ Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
¹¹ Observatoire de Genève, Département d’Astronomie de l’Université de Genève, 51 ch. des Maillettes, 1290 Versoix, Switzerland
¹² INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italy
¹³ Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, KY169SS, UK
¹⁴ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Spain
¹⁵ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90124 Palermo, Italy
¹⁶ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, Italy
¹⁷ SUPA, Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH93HJ, UK
¹⁸ Centre for Exoplanetary Science, University of Edinburgh, Edinburgh, UK

Received: 13 September 2019
Accepted: 18 December 2019

Abstract

Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (R_b = 1.613 ± 0.071 R_⊕) transiting the star on a short-period orbit (P_b = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to M_b = 5.60 ± 0.43 M_⊕. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R_⋆ = 1.22 ± 0.01 R_⊙ and mass of M_⋆ = 1.18 ± 0.04 M_⊙, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρ_b = 7.4 ± 1.1 g cm⁻³) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ~ 3480 K.