The CARMENES search for exoplanets around M dwarfs. The enigmatic planetary system GJ 4276: one eccentric planet or two planets in a 2:1 resonance?
Abstract
We report the detection of a Neptunemass exoplanet around the M4.0 dwarf GJ 4276 (G 232070) based on radial velocity (RV) observations obtained with the CARMENES spectrograph. The RV variations of GJ 4276 are best explained by the presence of a planetary companion that has a minimum mass of m_{b} sin i ≈ 16 M_{⊕} on a P_{b} = 13.35 day orbit. The analysis of the activity indicators and spectral diagnostics exclude stellar induced RV perturbations and prove the planetary interpretation of the RV signal. We show that a circular singleplanet solution can be excluded by means of a likelihood ratio test. Instead, we find that the RV variations can be explained either by an eccentric orbit or interpreted as a pair of planets on circular orbits near a period ratio of 2:1. Although the eccentric singleplanet solution is slightly preferred, our statistical analysis indicates that none of these two scenarios can be rejected with high confidence using the RV time series obtained so far. Based on the eccentric interpretation, we find that GJ 4276 b is the most eccentric (e_{b} = 0.37) exoplanet around an M dwarf with such a short orbital period known today.
Photometric measurements and Table C.1 are available at the CDS via anonymous ftp to http://cdsarc.ustrasbg.fr (ftp://130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/622/A153
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 2019
 DOI:
 10.1051/00046361/201834569
 arXiv:
 arXiv:1901.02367
 Bibcode:
 2019A&A...622A.153N
 Keywords:

 planetary systems;
 stars: individual: GJ 4276;
 stars: lowmass;
 methods: data analysis;
 methods: observational;
 techniques: radial velocities;
 Astrophysics  Earth and Planetary Astrophysics;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 15 pages, 12 figures, 3 tables, accepted for publication by A&