Masses for the seven planets in K2-32 and K2-233. Four diverse planets in resonant chain and the first young rocky worlds

J. Lillo-Box; T. A. Lopez; A. Santerne; L. D. Nielsen; S. C. C. Barros; M. Deleuil; L. Acuña; O. Mousis; S. G. Sousa; V. Adibekyan; D. J. Armstrong; D. Barrado; D. Bayliss; D. J. A. Brown; O. D. S. Demangeon; X. Dumusque; P. Figueira; S. Hojjatpanah; H. P. Osborn; N. C. Santos; S. Udry

doi:10.1051/0004-6361/202037896

paper

Masses for the seven planets in K2-32 and K2-233. Four diverse planets in resonant chain and the first young rocky worlds

arXiv:2006.01102 · doi:10.1051/0004-6361/202037896

Abstract

High-precision planetary densities are key to derive robust atmospheric properties for extrasolar planets. Measuring precise masses is the most challenging part, especially in multi-planetary systems. We measure the masses and densities of a four-planet near resonant chain system (K2-32), and a young ( $\sim 400$ Myr old) planetary system consisting of three close-in small planets (K2-233). We obtained 199 new HARPS observations for K2-32 and 124 for K2-233 covering a more than three year baseline. We find that K2-32 is a compact scaled-down version of the Solar System's architecture, with a small rocky inner planet (M $_{e} = 2. 1_{- 1.1}^{+ 1.3}$ ~M $_{\oplus}$ , P $_{e} \sim 4.35$ ~days) followed by an inflated Neptune-mass planet (M $_{b} = 15. 0_{- 1.7}^{+ 1.8}$ ~M $_{\oplus}$ , P $_{b} \sim 8.99$ ~days) and two external sub-Neptunes (M $_{c} = 8.1 \pm 2.4$ ~M $_{\oplus}$ , P $_{c} \sim 20.66$ ~days; M $_{d} = 6.7 \pm 2.5$ ~M $_{\oplus}$ , P $_{d} \sim 31.72$ ~days). K2-32 becomes one of the few multi-planetary systems with four or more planets known with measured masses and radii. Additionally, we constrain the masses of the three planets in K2-233. For the two inner Earth-size planets we constrain their masses to be smaller than M $_{b} < 11.3$ M $_{\oplus}$ (P $_{b} \sim 2.47$ ~days), M $_{c} < 12.8$ M $_{\oplus}$ (P $_{c} \sim 7.06$ ~days). The outer planet is a sub-Neptune size planet with an inferred mass of M $_{d} = 8. 3_{- 4.7}^{+ 5.2}$ M $_{\oplus}$ (M $_{d} < 21.1$ M $_{\oplus}$ , P $_{d} \sim 24.36$ ~days). Our observations of these two planetary systems confirm for the first time the rocky nature of two planets orbiting a young star, with relatively short orbital periods ( $< 7$ days). They provide key information for planet formation and evolution models of telluric planets. Additionally, the Neptune-like derived masses of the three planets K2-32 b, c, d puts them in a relatively unexplored regime of incident flux and planet mass, key for transmission spectroscopy studies.

Accepted for publication in A&A. 21 pages, 12 figures, 11 Tables

Masses for the seven planets in K2-32 and K2-233. Four diverse planets in resonant chain and the first young rocky worlds

Abstract

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