Four sub-Saturns with dissimilar densities: windows into planetary cores and envelopes

Petigura, Erik A. and Sinukoff, Evan and Lopez, Eric D. and Crossfield, Ian J. M. and Howard, Andrew W. and Brewer, John M. and Fulton, Benjamin J. and Isaacson, Howard T. and Ciardi, David R. and Howell, Steve B. and Everett, Mark E. and Horch, Elliott P. and Hirsch, Lea A. and Weiss, Lauren M. and Schlieder, Joshua E. (2017) Four sub-Saturns with dissimilar densities: windows into planetary cores and envelopes. The Astronomical Journal, 153 (4). ISSN 0004-6256

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Abstract

We present results from a Keck/HIRES radial velocity campaign to study four sub-Saturn-sized planets, K2-27b, K2-32b, K2-39b, and K2-108b, with the goal of understanding their masses, orbits, and heavy-element enrichment. The planets have similar sizes (RP=4.5-5.5 ), but have dissimilar masses (MP=16-60 ), implying a diversity in their core and envelope masses. K2-32b is the least massive (MP = 16.5 ± 2.7 M) and orbits in close proximity to two sub-Neptunes near a 3:2:1 period commensurability. K2-27b and K2-39b are significantly more massive at MP = 30.9 ± 4.6 M and MP = 39.8 ± 4.4 M, respectively, and show no signs of additional planets. K2-108b is the most massive at MP = 59.4 ± 4.4 M, implying a large reservoir of heavy elements of about ≈50 . Sub-Saturns as a population have a large diversity in planet mass at a given size. They exhibit remarkably little correlation between mass and size; sub-Saturns range from ≈6-60 M, regardless of size. We find a strong correlation between planet mass and host star metallicity, suggesting that metal-rich disks form more massive planet cores. The most massive sub-Saturns tend to lack detected companions and have moderately eccentric orbits, perhaps as a result of a previous epoch of dynamical instability. Finally, we observe only a weak correlation between the planet envelope fraction and present-day equilibrium temperature, suggesting that photo-evaporation does not play a dominant role in determining the amount of gas sub-Saturns accrete from their protoplanetary disks.


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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: 27 Oct 2017 04:11
Last Modified: 30 Oct 2017 01:19
Uncontrolled Keywords: planets and satellites; composition; planets and satellites; detection; dynamical evolution and stability
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Identification Number or DOI: 10.3847/1538-3881/aa5ea5
URI: http://eprints.usq.edu.au/id/eprint/32183

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