Mass determination of the three long-period Neptune- and sub-Neptune-sized planets transiting TOI-282

Abstract

TOI-282 is a bright (V=9.38) F8 main-sequence star known to host three transiting long-period ($P_b$=22.9 d, $P_c$=56.0 d, and $P_d$=84.3 d) small ($R_p\approx$ 2-4 $R_{\oplus }$) planets. The orbital period ratio of the two outermost planets, namely TOI-282 c and d, is close to the 3:2 commensurability, suggesting that the planets might be trapped in a mean motion resonance. We combined space-borne photometry from the TESS telescope with high-precision HARPS and ESPRESSO Doppler measurements to refine orbital parameters, measure the planetary masses, and investigate the architecture and evolution of the system. We performed a Markov chain Monte Carlo joint analysis of the transit light curves and radial velocity time series, and carried out a dynamical analysis to model transit timing variations and Doppler measurements along with N-body integration. In agreement with previous results, we found that TOI-282 b, c, and d have radii of $R_b=2.69\pm 0.23R_{\oplus }$, $R_c=4.13_{-0.14}^{+0.16}{R}_{\oplus }$, and $R_d=3.11\pm 0.15R_{\oplus }$, respectively. We measured planetary masses of $M_b=6.2\pm 1.6M_{\oplus }$, $M_c=9.2\pm 2.0M_{\oplus }$, and $M_d=5.8_{-1.1}^{+0.9}{M}_{\oplus }$, which imply mean densities of $\ddot{I}{}_b=1.8_{-0.6}^{+0.7}{\text{g cm}}^{-3}$, $\ddot{I}{}_c=0.7\pm 0.2{\text{g cm}}^{-3}$, and $\ddot{I}{}_d=1.1_{-0.2}^{+0.3}{\text{g cm}}^{-3}$, respectively. The three planets may be water worlds, making TOI-282 an interesting system for future atmospheric follow-up observations with JWST and ELT.

20 pages, 13 figures