Radii, masses, and transit-timing variations of the three-planet system orbiting the naked-eye star TOI-396

• DOI: 10.48550/arxiv.2411.14911
• Publication Date: 2024-11-22
• Authors: A. Bonfanti; I. Amateis; D. Gandolfi; L. Borsato; J. A. Egger; Patricio E. Cubillos; D. J. Armstrong; I. C. Leão; M. Fridlund; B. L. Canto Martins; S. G. Sousa; J. R. De Medeiros; L. Fossati; V. Adibekyan; A. Collier Cameron; S. Grziwa; K. W. F. Lam; E. Goffo; L. D. Nielsen; F. Rodler; Javier Alarcón; J. Lillo-Box; W. D. Cochran; R. Luque; S. Redfield; N. C. Santos; S. C. C. Barros; D. Bayliss; X. Dumusque; Marcelo Aron Fetz...; J. Livingston; F. Murgas; G. Nowak; Ares Osborn; H. P. Osborn; E. Pallé; Carina M. Persson; L. M. Serrano; P. A. Strøm; S. Udry; P. J. Wheatley
• Keywords: Star (game theory)

TOI-396 is an F6V star ($V\approx6.4$) orbited by three transiting planets. The orbital periods of the two innermost planets are close to 5:3 commensurability ($P_b \sim3.6$ d and $P_c \sim6.0$ d). To measure masses planets, refine their radii, investigate whether b c in MMR, we carried out HARPS RV observations retrieved photometric data from TESS. We extracted RVs via a skew-normal fit onto CCFs performed MCMC joint analysis Doppler measurements transit photometry, while employing breakpoint method remove stellar activity time series. also thorough TTV dynamical system. Our confirms that have similar sizes: $R_b=2.004_{-0.047}^{+0.045}R_{\oplus}$; $R_c=1.979_{-0.051}^{+0.054}R_{\oplus}$; $R_d=2.001_{-0.064}^{+0.063}R_{\oplus}$. For first time, determine for TOI-396b d: $M_b=3.55_{-0.96}^{+0.94}M_{\oplus}$ ($\rho_b=2.44_{-0.68}^{+0.69}$ g cm$^{-3}$) $M_d=7.1\pm1.6M_{\oplus}$ ($\rho_d=4.9_{-1.1}^{+1.2}$ cm$^{-3}$). results suggest quite unusual system architecture, with outermost planet being densest. reflex motion induced TOI-396c remains undetected our series, likely due proximity $P_c$ star's rotation period ($P_{\mathrm{rot}}=6.7\pm1.3$ discovered display significant TTVs. While returns formally precise mass ($M_{c,\mathrm{dyn}}=2.24^{+0.13}_{-0.67}M_{\oplus}$), result might not be accurate owing poor sampling phase. conclude to-, but of- MMR. numerical simulation suggests semi-amplitudes up 5 hours over temporal baseline $\sim$5.2 years.