Two Jovian Planets around the Giant Star HD 202696: A Growing Population of Packed Massive Planetary Pairs around Massive Stars?
Abstract
We present evidence for a new two-planet system around the giant star HD 202696 (=HIP 105056, BD +26 4118). The discovery is based on public HIRES radial velocity (RV) measurements taken at Keck Observatory between 2007 July and 2014 September. We estimate a stellar mass of {1.91}-0.14+0.09{M}⊙ for HD 202696, which is located close to the base of the red giant branch. A two-planet self-consistent dynamical modeling MCMC scheme of the RV data followed by a long-term stability test suggests planetary orbital periods of P b = {517.8}-3.9+8.9 and P c = {946.6}-20.9+20.7 days, eccentricities of e b = {0.011}-0.011+0.078 and e c = {0.028}-0.012+0.065, and minimum dynamical masses of m b = {2.00}-0.10+0.22 and m c = {1.86}-0.23+0.18 M Jup, respectively. Our stable MCMC samples are consistent with orbital configurations predominantly in a mean period ratio of 11:6 and its close-by high-order mean-motion commensurabilities with low eccentricities. For the majority of the stable configurations, we find an aligned or anti-aligned apsidal libration (i.e., Δω librating around 0° or 180°), suggesting that the HD 202696 system is likely dominated by secular perturbations near the high-order 11:6 mean-motion resonance. The HD 202696 system is yet another Jovian-mass pair around an intermediate-mass star with a period ratio below the 2:1 mean-motion resonance. Therefore, the HD 202696 system is an important discovery that may shed light on the primordial disk-planet properties needed for giant planets to break the strong 2:1 mean-motion resonance and settle in more compact orbits.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 2019
- DOI:
- 10.3847/1538-3881/aafa11
- arXiv:
- arXiv:1901.01935
- Bibcode:
- 2019AJ....157...93T
- Keywords:
-
- planetary systems;
- planets and satellites: detection;
- planets and satellites: dynamical evolution and stability;
- techniques: radial velocities;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Accepted for publication in AJ on 18th December 2018. 15 pages, 11 Figures, 4 Tables (this .v2 is copy corrected and identical with the published paper)