Two transiting low density sub-Saturns from K2

Petigura, Erik A. and Howard, Andrew W. and Lopez, Eric D. and Deck, Katherine M. and Fulton, Benjamin J. and Crossfield, Ian J. M. and Ciardi, David R. and Chiang, Eugene and Lee, Eve J. and Isaacson, Howard and Beichman, Charles A. and Hansen, Brad M. S. and Schlieder, Joshua E. and Sinukoff, Evan (2016) Two transiting low density sub-Saturns from K2. The Astrophysical Journal, 818 (1). pp. 36-46. ISSN 0004-637X

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Abstract

We report the discovery and confirmation of K2-24 b and c, two sub-Saturn planets orbiting a bright (V = 11.3), metal-rich ([Fe/H] = 0.42 ± 0.04 dex) G3 dwarf in the K2 Campaign 2 field. The planets are 5.68 ± 0.56 R⊕ and 7.82 ± 0.72 R⊕ and have orbital periods of 20.8851 ± 0.0003 days and 42.3633 ± 0.0006 days, near the 2:1 mean-motion resonance. We obtained 32 radial velocities with Keck/HIRES and detected the reflex motion due to K2-24 b and c. These planets have masses of 21.0 ± 5.4 M⊕ and 27.0 ± 6.9 M⊕, respectively. With low densities of 0.63 ± 0.25 g cm-3 and 0.31 ± 0.12 g cm-3, respectively, the planets require thick envelopes of H/He to explain their large sizes and low masses. Interior structure models predict that the planets have fairly massive cores of 17.6 ± 4.3 M⊕ and 16.1, ± 4.2 M⊕, respectively. They may have formed exterior to their present locations, accreted their H/He envelopes at large orbital distances, and migrated in as a resonant pair. The proximity to resonance, large transit depths, and host star brightness offers rich opportunities for TTV follow-up. Finally, the low surface gravities of the K2-24 planets make them favorable targets for transmission spectroscopy by Hubble Space Telescope, Spitzer, and James Webb Space Telescope.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: No Faculty
Date Deposited: 12 Jun 2017 22:45
Last Modified: 27 Jun 2017 00:22
Uncontrolled Keywords: planets and satellites; stars; EPIC-203771098; photometric; spectroscopic
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.3847/0004-637X/818/1/36
URI: http://eprints.usq.edu.au/id/eprint/32193

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