TBV vs. probability density after 10 000 MC simulations for three cases. In case 1 (orange) the star is at rest and the spot modulated at 9 d; in case 2 (blue) the star is Doppler shifted with a semi-amplitude of 0.3 km s⁻¹, keeping all other parameters the same as in case 1. In case 3 (green) we test a scenario proposed by Donati et al. (2024), i.e. a contribution from material in the inner disk on the CO lines, that could cause the 25.2 d periodicity. The distributions represent the TBVs of the BIS span plots. The grey dotted line is the observed TBV for the SPIRou BIS span vs. RVs plot.