Dynamics and Formation of the Near-resonant K2-24 System: Insights from Transit-timing Variations and 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 and 7.5 , respectively. The two planets have orbital periods of 20.9 days and 42.4 days, residing only 1% outside the nominal 2:1 mean-...
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Published in | The Astronomical journal Vol. 156; no. 3; pp. 89 - 100 |
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Main Authors | , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Madison
The American Astronomical Society
01.09.2018
IOP Publishing |
Subjects | |
Online Access | Get full text |
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Summary: | 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 and 7.5 , 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 . 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 and , 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 % and %. 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 50%. |
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Bibliography: | AAS09843 The Solar System, Exoplanets, and Astrobiology |
ISSN: | 0004-6256 1538-3881 |
DOI: | 10.3847/1538-3881/aaceac |