Abstract The young TOI-451 planetary system, aged 125 Myr, provides a unique opportunity to test theories of planetary internal structures and atmospheric mass loss through examination of its three transiting planets. We present an exhaustive photometric and spectroscopic follow-up to determine the orbital and physical properties of the system. We perform multidimensional Gaussian Process regression with the code pyaneti on spectroscopic time-series and NGTS/LCO light curves to disentangle the stellar and planetary signal in ESPRESSO radial velocities. We show how contemporaneous photometry serves as an activity indicator to inform RV modelling within a multidimensional Gaussian Processes framework. We argue that this can be exploited when spectroscopic observations are adversely affected by low signal-to-noise and/or poor sampling. We estimate the Doppler semi-amplitudes of kb = 2. 6-₁. ₂^+1. 1 m s−1, kc = 1. 2-₀. ₈^+1. 0 m s−1 and kd = 2. 7 ± 1. 2 m s−1. This translates in 2-σ mass estimates for TOI-451 b and d of Mb = 4. 7-₂. ₂^+2. 1 M⊕ and Md = 10. 2-₄. ₅^+4. 6 M⊕ ; as well as a mass upper limit for TOI-451 c of Mc 11. 5 M⊕. The derived planetary properties suggest that planets c and d contain significant hydrogen-rich envelopes. The inferred parameters of TOI-451 b are consistent with either a rocky world that still retains a small hydrogen envelope or a water world. These insights make the TOI-451 system an ideal laboratory for future follow-up studies aimed at measuring atmospheric compositions, detecting atmospheric mass-loss signatures, and further exploring planetary formation and evolution processes.
Barragán et al. (Wed,) studied this question.
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