Mass, gas, and Gauss around a T Tauri Star with SPIRou

Studies of young planets help us understand planet evolution and investigate important evolutionary processes such as atmospheric escape. We monitored a 3 Myr-old T Tauri star with a transiting planet and a transitional disk, with the SPIRou infrared spectropolarimeter on the Canada-France-Hawaii Telescope. Using these data, we constrained the mass and density of the Jupiter-size companion to $<$0.16 and $<$0.23 respectively (90% upper limits). These rule out a Jovian-like object and support the hypothesis that it is an ancestor to the numerous sub-Neptunes found around mature stars. We unambiguously detected magnetic fields at the stellar surface, small-scale fields reaching 1.5 kG and the large-scale field mostly consisting of a 0.80-0.95 kG dipole inclined by 5-15 to the rotation axis. Accretion onto the star is low and/or episodic at a maximum rate of ≃10^-11 indicating that is most likely in a magnetic ``propeller" regime, presumably explaining the star's slow rotation (11.3 d). We discovered persistent Doppler-shifted absorption in a metastable line, clear evidence for a magnetized wind from a gaseous inner disk. Variability in absorption suggests structure in the disk wind that could reflect disk-planet interactions.