The HARPS search for southern extra-solar planets XLIII. A compact system of four super-Earth planets orbiting HD 215152

J.-B Delisle (1, 2) , D. Segransan (2) , X. Dumusque (2) , R F Diaz (2, 3) , F. Bouchy (4) , C. Lovis (2) , F Pepe (2) , S. Udry (2) , R. Alonso (5) , W. Benz (6) , A Coffinet (2) , A Collier Cameron (7) , M. Deleuil (4) , P. Figueira (8) , Michael Gillon , G Lo Curto (9) , M. Mayor (2) , C. Mordasini (6) , F Motalebi (2) , C. Moutou (4) , D Pollacco (10) , E Pompei (9) , D Queloz (2, 11) , N C Santos (12) , A Wyttenbach (2)

1 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
2 ObsGE - Observatoire Astronomique de l'Université de Genève
3 UBA - Universidad de Buenos Aires [Buenos Aires]
4 LAM - Laboratoire d'Astrophysique de Marseille
5 CBMSO - Centro de Biología Molecular Severo Ochoa [Madrid]
6 Physikalisches Institut [Bern]
7 University of St Andrews [Scotland]
8 CAUP - Centro de Astrofísica da Universidade do Porto
9 ESO - European Southern Observatory
10 University of Warwick [Coventry]
11 Cavendish Laboratory
12 Universidade do Porto = University of Porto

We report the discovery of four super-Earth planets around HD 215152, with orbital periods of 5.76, 7.28, 10.86, and 25.2 d, and minimum masses of 1.8, 1.7, 2.8, and 2.9 M ⊕ respectively. This discovery is based on 373 high-quality radial velocity measurements taken by HARPS over 13 years. Given the low masses of the planets, the signal-to-noise ratio is not sufficient to constrain the planet eccentricities. However, a preliminary dynamical analysis suggests that eccentricities should be typically lower than about 0.03 for the system to remain stable. With two pairs of planets with a period ratio lower than 1.5, with short orbital periods, low masses, and low eccentricities, HD 215152 is similar to the very compact multi-planet systems found by Kepler, which is very rare in radial-velocity surveys. This discovery proves that these systems can be reached with the radial-velocity technique, but characterizing them requires a huge amount of observations.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]

J.-B Delisle, D. Segransan, X. Dumusque, R F Diaz, F. Bouchy, et al.. The HARPS search for southern extra-solar planets XLIII. A compact system of four super-Earth planets orbiting HD 215152. Astronomy and Astrophysics - A&A, 2018, 614, pp.A133. ⟨10.1051/0004-6361/201732529⟩. ⟨hal-02109207⟩