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

DELISLE, J.-B.; SÉGRANSAN, D.; DUMUSQUE, X.; DÍAZ, R.F.; BOUCHY, F.; LOVIS, C.; PEPE, F.; UDRY, S.; ALONSO, R.; BENZ, W.; COFFINET, A.; COLLIER CAMERON, A.; DELEUIL, M.; FIGUEIRA, P.; GILLON, M.; LO CURTO, G.; MAYOR, M.; MORDASINI, C.; MOTALEBI, F.; MOUTOU, C.; POLLACCO, D.; POMPEI, E.; QUELOZ, D.; SANTOS, N.C.; WYTTENBACH, A.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2018 vol. 614

0004-6361

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 yr. 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.