SPIRou Legacy Survey: RV Detection of TRAPPIST-1 b

The TRAPPIST-1 system is well-known for its seven transiting Earth-sized exoplanets. It has been extensively studied and characterized, notably with light curves to infer the rotation period of the star, and transit-timing variations (TTVs) to precisely measure the mass of the planets. Using the infrared spectropolarimeter SPIRou, we aim to verify those values with a thorough radial velocity (RV) analysis of the system grounded in the line-by-line (LBL) framework. We monitor stellar activity using gaussian processes (GP) trained on the differential spectral line width. This provides a photometry-independent rotation period spanning more than two years and with it, insights into the evolution of the stellar surface. We then use this GP to inform the stellar activity component of a joint RV model. With fixed mass ratios from the current most precise TTV measurements for the planetary component, we obtain a 3.4σ RV detection for TRAPPIST-1 b, confirming the TTV masses.