Precise radial velocities of giant stars XIII. A second Jupiter orbiting in 4:3 resonance in the 7 CMa system

• Published in: arXiv.org 2019-10
• Main Authors: Luque, R, Trifonov, T, Reffert, S, Quirrenbach, A, Lee, M H, Albrecht, S, Andersen, M Fredslund, Antoci, V, Grundahl, F, Schwab, C, Wolthoff, V
• Format: Article
• Language: English
• Subjects: Collision avoidance; Giant stars; Orbital mechanics; Orbital resonances (celestial mechanics); Planet formation; Planetary evolution; Planets; Stability analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1910.05853

We report the discovery of a second planet orbiting the K giant star 7 CMa based on 166 high-precision radial velocities obtained with Lick, HARPS, UCLES and SONG. The periodogram analysis reveals two periodic signals of approximately 745 and 980 d, associated to planetary companions. A double-Keplerian orbital fit of the data reveals two Jupiter-like planets with minimum masses \(m_b\sin i \sim 1.9 \,\mathrm{M_{J}}\) and \(m_c\sin i \sim 0.9 \,\mathrm{M_{J}}\), orbiting at semi-major axes of \(a_b \sim 1.75\,\mathrm{au}\) and \(a_c \sim 2.15\,\mathrm{au}\), respectively. Given the small orbital separation and the large minimum masses of the planets close encounters may occur within the time baseline of the observations, thus, a more accurate N-body dynamical modeling of the available data is performed. The dynamical best-fit solution leads to collision of the planets and we explore the long-term stable configuration of the system in a Bayesian framework, confirming that 13% of the posterior samples are stable for at least 10 Myr. The result from the stability analysis indicates that the two-planets are trapped in a low-eccentricity 4:3 mean-motion resonance. This is only the third discovered system to be inside a 4:3 resonance, making it very valuable for planet formation and orbital evolution models.