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

Petigura, Erik A. and Benneke, Björn and Batygin, Konstantin and Fulton, Benjamin J. and Werner, Michael and Krick, Jessica E. and Gorjian, Varoujan and Sinukoff, Evan and Deck, Katherine M. and Mills, Sean M. and Deming, Drake (2018) Dynamics and Formation of the Near-resonant K2-24 System: Insights from Transit-timing Variations and Radial Velocities. Astronomical Journal, 156 (3). Art. No. 89. ISSN 1538-3881. http://resolver.caltech.edu/CaltechAUTHORS:20180809-101844353

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Abstract

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⊕ and 7.5 R⊕, 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 ~ e_2 ~ 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^(+2.2)_(-2.1) M⊕ and 15.4^(+1.9)_(-1.8) M⊕, 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^(+5)_(-3)%. 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 ∫_(env) ≈ 50%.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-3881/aaceacDOIArticle
https://arxiv.org/abs/1806.08959arXivDiscussion Paper
ORCID:
AuthorORCID
Petigura, Erik A.0000-0003-0967-2893
Benneke, Björn0000-0001-5578-1498
Fulton, Benjamin J.0000-0003-3504-5316
Sinukoff, Evan0000-0002-5658-0601
Deming, Drake0000-0001-5727-4094
Additional Information:© 2018 The American Astronomical Society. Received 2018 February 20; revised 2018 May 30; accepted 2018 June 13; published 2018 August 9. We thank the anonymous reviewer for helpful suggestions that improved this manuscript. E.A.P. acknowledges support from Hubble Fellowship grant HST-HF2-51365.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555. This work made use of NASA's Astrophysics Data System Bibliographic Services. We thank Spitzer Science Center Director Tom Soifer for awarding discretionary time. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. We thank Andrew Howard, Lea Hirsch, Lauren Weiss, Howard Isaacson, and Molly Kosiarek for their assistance with the Keck/HIRES observations. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Software: Astropy (Astropy Collaboration et al. 2013), batman (Kreidberg 2015), ChainConsumer (Hinton 2016), emcee (Foreman-Mackey et al. 2013), isoclassify (Huber et al. 2017), lmfit (Newville et al. 2014), matplotlib (Hunter 2007), Mercury (Chambers 1999), numpy/scipy (van der Walt et al. 2011), pandas (McKinney 2010), and RadVel (Fulton et al. 2018). Facilities: Keck:I (HIRES) - , Spitzer - , Kepler - .
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51365.001-A
NASANAS 5-26555
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:planets and satellites: dynamical evolution and stability – planets and satellites: formation – planets and satellites: individual (K2-24b,K2-24c) – techniques: radial velocities
Record Number:CaltechAUTHORS:20180809-101844353
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180809-101844353
Official Citation:Erik A. Petigura et al 2018 AJ 156 89
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88688
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Aug 2018 17:56
Last Modified:09 Aug 2018 17:56

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