Longperiod Jovian Tilts the Orbits of Two subNeptunes Relative to Stellar Spin Axis in Kepler129
Abstract
We present the discovery of Kepler129 d ( ${P}_{d}={7.2}_{0.3}^{+0.4}$ yr, $m\sin {i}_{d}={8.3}_{0.7}^{+1.1}\,{M}_{\mathrm{Jup}}$ , ${e}_{d}={0.15}_{0.05}^{+0.07}$ ) based on six years of radialvelocity observations from Keck/HIRES. Kepler129 also hosts two transiting subNeptunes: Kepler129 b (P_{b} = 15.79 days, r_{b} = 2.40 ± 0.04 R_{⊕}) and Kepler129 c (P_{c} = 82.20 days, r_{c} = 2.52 ± 0.07 R_{⊕}) for which we measure masses of m_{b} < 20 M_{⊕} and ${m}_{c}={43}_{12}^{+13}\,{M}_{\oplus }$ . Kepler129 is a hierarchical system consisting of two tightly packed inner planets and a massive external companion. In such a system, two inner planets precess around the orbital normal of the outer companion, causing their inclinations to oscillate with time. Based on an asteroseismic analysis of Kepler data, we find tentative evidence that Kepler129 b and c are misaligned with stellar spin axis by ≳38°, which could be torqued by Kepler129 d if it is inclined by ≳19° relative to inner planets. Using Nbody simulations, we provide additional constraints on the mutual inclination between Kepler129 d and inner planets by estimating the fraction of time during which two inner planets both transit. The probability that two planets both transit decreases as their misalignment with Kepler129 d increases. We also find a more massive Kepler129 c enables the two inner planets to become strongly coupled and more resistant to perturbations from Kepler129 d. The unusually high mass of Kepler129 c provides a valuable benchmark for both planetary dynamics and interior structure, since the bestfit mass is consistent with this 2.5 R_{⊕} planet having a rocky surface.
 Publication:

The Astronomical Journal
 Pub Date:
 September 2021
 DOI:
 10.3847/15383881/ac0634
 arXiv:
 arXiv:2105.03446
 Bibcode:
 2021AJ....162...89Z
 Keywords:

 Radial velocity;
 Asteroseismology;
 Exoplanet dynamics;
 1332;
 73;
 490;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 submitted to AJ, revised based on reviewer report