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The HARPS search for southern extra-solar planets XLII.
A system of Earth-mass planets around the nearby M dwarf YZ Ceti

N. Astudillo-Defru, R. F. Dı́az, X. Bonfils, J.-M. Almenara, F. Bouchy, X. Delfosse, T. Forveille, C. Lovis, M. Mayor, F. Murgas Alcaino, F. Pepe, N. C. Santos, D. Sťgransan, S. Udry, A. WŁnsche

Exoplanet surveys have shown that systems with multiple low-mass planets on compact orbits are common. Except for a few cases, however, the masses of these planets are generally unknown. At the very end of the main sequence, host stars have the lowest mass and hence offer the largest reflect motion for a given planet. In this context, we monitored the low-mass (0.13 M⊙) M dwarf YZ Cet (GJ 54.1, HIP 5643) intensively and obtained radial velocities and stellar-activity indicators derived from spectroscopy and photometry, respectively. We find strong evidence that it is orbited by at least three planets in compact orbits (POrb = 1.97, 3.06, 4.66 days), with the inner two near a 2:3 mean-motion resonance. The minimum masses are comparable to 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 the lowest masses measured by radial velocity so far. We note the possibility 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 the system parameters. At 3.6 parsecs, YZ Cet is the nearest multi-planet system detected to date.

stars: individual: YZ Cet; planetary systems; stars: late-type; techniques: radial velocities; Astrophysics - Earth and Planetary Astrophysics

Astronomy and Astrophysics
Volume 605, Article Number L11
2017 September

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda√ß√£o para a Ci√™ncia e a Tecnologia
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