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Characterization of the K2-38 planetary system

2020; EDP Sciences; Volume: 641; Linguagem: Inglês

10.1051/0004-6361/202038187

1432-0746

B. Toledo-Padrón, C. Lovis, A. Suárez Mascareño, S. C. C. Barros, J. I. Gónzalez Hernández, A. Sozzetti, F. Bouchy, M. R. Zapatero Osorio, R. Rébolo, S. Cristiani, F. Pepe, N. C. Santos, S. G. Sousa, H. M. Tabernero, J. Lillo-Box, D. Bossini, V. Adibekyan, R. Allart, M. Damasso, V. D’Odorico, P. Figueira, B. Lavie, G. Lo Curto, A. Mehner, G. Micela, A. Modigliani, N. J. Nunes, Ε. Πάλλη, Manuel Abreu, Michael Affolter, Y. Alibert, Matteo Aliverti, C. Allende Prieto, D. R. Alves, M. Amate, G. Ávila, Veronica Baldini, Timothy Bandy, S. Benatti, W. Benz, Andrea Bianco, C. Broeg, Alexandre Cabral, Giorgio Calderone, R. Cirami, João M. P. Coelho, P. Conconi, Igor Coretti, Claudio Cumani, G. Cupani, S. Deiries, H. Dekker, Bernard Délabre, O. D. S. Demangeon, P. Di Marcantonio, D. Ehrenreich, A. Fragoso, Ludovic Genolet, Matteo Genoni, R. Génova-Santos, Ifan G. Hughes, O. Iwert, J. Knudstrup, Marco Landoni, J. L. Lizon, C. Maire, A. Manescau, C. J. A. P. Martins, D. Mégevand, P. Molaro, M. J. P. F. G. Monteiro, M. A. Monteiro, M. Moschetti, E. Mueller, Luca Oggioni, A. Oliveira, M. Oshagh, Giorgio Pariani, L. Pasquini, E. Poretti, J. L. Rasilla, Edoardo Maria Alberto Redaelli, Marco Riva, S. Santana Tschudi, P. Santin, Pedro Santos, A. Segovia, D. Sosnowska, P. Spanò, F. Tenegi, S. Udry, Alessio Zanutta, F. M. Zerbi,

Astronomy and Astrophysical Research

We characterized the transiting planetary system orbiting the G2V star K2-38 using the new-generation echelle spectrograph ESPRESSO. We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets. Using 43 ESPRESSO high-precision radial velocity measurements taken over the course of 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a MCMC analysis, significantly improving their mass measurements. Using ESPRESSO spectra, we derived the stellar parameters, $T_{\rm eff}$=5731$\pm$66, $\log g$=4.38$\pm$0.11~dex, and $[Fe/H]$=0.26$\pm$0.05~dex, and thus the mass and radius of K2-38, $M_{\star}$=1.03 $^{+0.04}_{-0.02}$~M$_{\oplus}$ and $R_{\star}$=1.06 $^{+0.09}_{-0.06}$~R$_{\oplus}$. We determine new values for the planetary properties of both planets. We characterize K2-38b as a super-Earth with $R_{\rm P}$=1.54$\pm$0.14~R$_{\rm \oplus}$ and $M_{\rm p}$=7.3$^{+1.1}_{-1.0}$~M$_{\oplus}$, and K2-38c as a sub-Neptune with $R_{\rm P}$=2.29$\pm$0.26~R$_{\rm \oplus}$ and $M_{\rm p}$=8.3$^{+1.3}_{-1.3}$~M$_{\oplus}$. We derived a mean density of $\rho_{\rm p}$=11.0$^{+4.1}_{-2.8}$~g cm$^{-3}$ for K2-38b and $\rho_{\rm p}$=3.8$^{+1.8}_{-1.1}$~g~cm$^{-3}$ for K2-38c, confirming K2-38b as one of the densest planets known to date. The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by a rocky model with a H2 envelope. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the radial velocity time-series whose origin could be linked to a 0.25-3~M$_{\rm J}$ planet or stellar activity.