Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. III. A High Mass and Low Envelope Fraction for the Warm Neptune K2-55bстатья из журнала
Аннотация: K2-55b is a Neptune-sized planet orbiting a K7 dwarf with a radius of $0.715^{+0.043}_{-0.040}R_\odot$, a mass of $0.688\pm0.069 M_\odot$, and an effective temperature of $4300^{+107}_{-100}$K. Having characterized the host star using near-infrared spectra obtained at IRTF/SpeX, we observed a transit of K2-55b with Spitzer/IRAC and confirmed the accuracy of the original K2 ephemeris for future follow-up transit observations. Performing a joint fit to the Spitzer/IRAC and K2 photometry, we found a planet radius of $4.41^{+0.32}_{-0.28} R_\oplus$, an orbital period of $2.84927265_{-6.42\times10^{-6}}^{+6.87\times10^{-6}}$ days, and an equilibrium temperature of roughly 900K. We then measured the planet mass by acquiring twelve radial velocity (RV) measurements of the system using HIRES on the 10m Keck I Telescope. Our RV data set precisely constrains the mass of K2-55b to $43.13^{+5.98}_{-5.80} M_\oplus$, indicating that K2-55b has a bulk density of $2.8_{-0.6}^{+0.8}$ g cm$^{-3}$ and can be modeled as a rocky planet capped by a modest H/He envelope ($M_{\rm envelope} = 12\pm3\% M_p$). K2-55b is denser than most similarly sized planets, raising the question of whether the high planetary bulk density of K2-55b could be attributed to the high metallicity of K2-55. The absence of a substantial volatile envelope despite the large mass of K2-55b poses a challenge to current theories of gas giant formation. We posit that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion or that K2-55b was stripped of its envelope by a late giant impact.
Год издания: 2018
Авторы: Courtney D. Dressing, Evan Sinukoff, Benjamin J. Fulton, Eric Lopez, Charles Beichman, Andrew W. Howard, Heather A. Knutson, M. W. Werner, Björn Benneke, Ian J. M. Crossfield, Howard Isaacson, Jessica Krick, Varoujan Gorjian, John H. Livingston, Erik A. Petigura, Joshua E. Schlieder, Rachel Akeson, Konstantin Batygin, Jessie L. Christiansen, David R. Ciardi, Justin R. Crepp, Erica J. Gonzales, Kevin K. Hardegree-Ullman, Lea A. Hirsch, Molly Kosiarek, Lauren M. Weiss
Издательство: Institute of Physics
Источник: The Astronomical Journal
Ключевые слова: Stellar, planetary, and galactic studies, Astro and Planetary Science, Astronomical and nuclear sciences
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Том: 156
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Страницы: 70–70