GJ 357: A low-mass planetary system uncovered by precision radial-velocities and dynamical simulations

DOI: 
10.1093/mnras/stz2937
Publication date: 
01/10/2019
Main author: 
Jenkins, J. S.
IAA authors: 
Suárez, Juan C.
Authors: 
Jenkins, J. S.;Pozuelos, F. J.;Tuomi, M.;Berdiñas, Z. M.;Díaz, M. R.;Vines, J. I.;Suárez, Juan C.;Peña Rojas, P. A.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
5585-5595
Abstract: 
We report the detection of a new planetary system orbiting the nearby M2.5V star GJ 357, using precision radial-velocities from three separate echelle spectrographs, HARPS, HiRES, and UVES. Three small planets have been confirmed in the system, with periods of 9.125±0.001, 3.9306±0.0003, and 55.70±0.05 days, and minimum masses of 3.33±0.48, 2.09±0.32, and 6.72±0.94 M<SUB>⊕</SUB>, respectively. The second planet in our system, GJ 357c, was recently shown to transit by the Transiting Exoplanet Survey Satellite (TESS; Luque et al. 2019), but we could find no transit signatures for the other two planets. Dynamical analysis reveals the system is likely to be close to coplanar, is stable on Myrs timescales, and places strong upper limits on the masses of the two non-transiting planets b and d of 4.25 and 11.20 M<SUB>⊕</SUB>, respectively. Therefore, we confirm the system contains at least two super-Earths, and either a third super-Earth or mini-Neptune planet. GJ 357b &amp; c are found to be close to a 7:3 mean motion resonance, however no libration of the orbital parameters was found in our simulations. Analysis of the photometric lightcurve of the star from the TESS, when combined with our radial-velocities, reveal GJ 357c has an absolute mass, radius, and density of 2.248^{+0.117}_{-0.120} M<SUB>⊕</SUB>, 1.167^{+0.037}_{-0.036} R<SUB>⊕</SUB>, and 7.757^{+0.889}_{-0.789} gcm<SUP>-3</SUP>, respectively. Comparison to super-Earth structure models reveals the planet is likely an iron dominated world. The GJ 357 system adds to the small sample of low-mass planetary systems with well constrained masses, and further observational and dynamical follow-up is warranted to better understand the overall population of small multi-planet systems in the solar neighbourhood.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85079600948&doi=10.1093%2fmnras%2fstz2937&partnerID=40&md5=df97dfb1adfe79e1edb9c38240feb1fe
ADS Bibcode: 
2019MNRAS.490.5585J
Keywords: 
stars: planetary systems;stars: activity;stars: low-mass;planets and satellites: detection;planets and satellites: dynamical evolution and stability;Astrophysics - Earth and Planetary Astrophysics;Astrophysics - Solar and Stellar Astrophysics