The HARPS search for southern extra-solar planets

ASTUDILLO-DEFRU, N.; DÍAZ, R. F.; BONFILS, X.; ALMENARA, J. M.; DELISLE, J.-B.; BOUCHY, F.; DELFOSSE, X.; FORVEILLE, T.; LOVIS, C.; MAYOR, M.; MURGAS, F.; PEPE, F.; SANTOS, N. C.; SÉGRANSAN, D.; UDRY, S.; WÜNSCHE, A.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2017 vol. 605

0004-6361

Exoplanet surveys have shown that systems with multiple low-mass planetson compact orbits are common. Except for a few cases, however, themasses of these planets are generally unknown. At the very end of themain sequence, host stars have the lowest mass and hence offer thelargest reflect motion for a given planet. In this context, we monitoredthe low-mass (0.13 M⊙) M dwarf YZ Cet (GJ 54.1, HIP 5643)intensively and obtained radial velocities and stellar-activityindicators derived from spectroscopy and photometry, respectively. Wefind strong evidence that it is orbited by at least three planets incompact orbits (POrb = 1.97, 3.06, 4.66 days), with the innertwo near a 2:3 mean-motion resonance. The minimum masses are comparableto the mass of Earth (M sin I = 0.75 ± 0.13, 0.98 ± 0.14,and 1.14 ± 0.17 M⊕), and they are also thelowest masses measured by radial velocity so far. We note thepossibility for a fourth planet with an even lower mass of M sin I =0.472 ± 0.096 M⊕ at POrb = 1.04 days.An n-body dynamical model is used to place further constraints on thesystem parameters. At 3.6 parsecs, YZ Cet is the nearest multi-planetsystem detected to date.