Two nearby young exoplanet systems hosting warm transiting super-Earths

The discovery and characterisation of young exoplanetary systems play a crucial role in deepening our understanding of planetary formation processes and their orbital and physical evolution. However, characterising young exoplanets around young and active stellar hosts poses significant challenges. These stars normally exhibit rapid rotation, and strong chromospheric and magnetic activity (e.g., resulting in a stellar surface rich in spots and faculae), which can affect both spectroscopic and photometric measurements. Consequently, stellar activity can produce periodic signals that may mimic false-positive planetary Doppler signals or hamper the detection of a genuine planetary signal. Therefore, its thorough removal from exoplanet data is essential for accurately detecting and characterising exoplanets. Our study aims to characterise young exoplanets through high-precision radial velocity monitoring using the ground-based spectrometer HARPS-N at TNG (Telescopio Nazionale Galileo) within the Young Objects sub-program of the Global Architecture of Planetary Systems (GAPS) project. We report the detailed characterisation of two similar warm transiting exoplanet systems detected by TESS (with follow-up observations by CHEOPS) around two nearby young K dwarf stars. In particular, we focused on the impact of stellar activity on the radial velocities (RVs) in the attempt to derive accurate planet masses and eccentricities. We analytically corrected the contributions of the BIS Span and logR'hk activity indices from the RV data. The correlation between RV and the activity indices was significantly reduced by this correction, revealing previously obscured planetary signals. Our orbital analyses were performed using the Exo-Striker exoplanet toolbox (Trifonov 2019), which provides a graphical user interface for operating a broad range of tools for detailed transit and Doppler data analysis. It enables efficient control of input and output planetary and stellar parameters, priors, and spectral activity indicators analysis. The transit and RV data were jointly fitted using a Nested Sampling scheme for Bayesian parameter posterior analysis and error estimation. The stellar activity was modelled with the Gaussian Processes model, featuring a quasi-periodic rotational kernel (Foreman-Mackey et al. 2017). This modelling scheme allowed us to ascertain the stellar rotation period and constrain the orbital and physical parameters of the detected exoplanets. Our work reveals that each of the two stars hosts a warm Super-Earth-sized planet with negligible eccentricities. These young systems are vital targets for follow-up observations with JWST and the upcoming ARIEL space telescope to derive their atmospheric constituents and unravel their origin and formation stages.