Dynamics and Formation of the Near-resonant K2-24 System: Insights from Transit-timing Variations and Radial Velocities

作者：Petigura Erik A^*; Benneke Bjorn; Batygin Konstantin; Fulton Benjamin J; Werner Michael; Krick Jessica E; Gorjian Varoujan; Sinukoff Evan; Deck Katherine M; Mills Sean M; Deming Drake

来源：Astronomical Journal, 2018, 156(3): 89.

DOI：10.3847/1538-3881/aaceac

• planets and satellites: dynamical evolution and stability
• planets and satellites: formation
• planets and satellites: individual (K2-24b,K2-24c)
• techniques: radial velocities

While planets between the size of Uranus and Saturn are absent within the solar system, the star K2-24 hosts two such planets, K2-24b and c, with radii equal to 5.4 R-circle plus and 7.5 R-circle plus, respectively. The two planets have orbital periods of 20.9 days and 42.4 days, residing only 1% outside the nominal 2:1 mean-motion resonance. In this work, we present results from a coordinated observing campaign to measure planet masses and eccentricities that combines radial velocity measurements from Keck/HIRES and transit-timing measurements from K2 and Spitzer. K2-24b and c have low, but nonzero, eccentricities of e(1)similar to e(2) similar to 0.08. The low observed eccentricities provide clues to the formation and dynamical evolution of K2-24b and K2-24c, suggesting that they could be the result of stochastic gravitational interactions with a turbulent protoplanetary disk, among other mechanisms. K2-24b and c are 19.0(-2.)(1)(+2.2 )M(circle plus) and 15.4(-1.8)(+1.9) M-circle plus, respectively; K2-24c is 20% less massive than K2-24b, despite being 40% larger. Their large sizes and low masses imply large envelope fractions, which we estimate at 26(-3)(+3)% and 52(-3)(+5%). In particular, K2-24c' s large envelope presents an intriguing challenge to the standard model of core-nucleated accretion that predicts the onset of runaway accretion when f(env) approximate to 50%.

• 出版日期2018-9