Application of the rigid rotator model to the star HP Tau/G2, showing stellar mass (M) as a function of the rotation rate. The model incorporates observational constraints: projected rotational velocity ﹩v\sin i\approx ﹩ 127 km s⁻¹, and projected equatorial radius ﹩R\sin i\approx 3.1{R}_{\odot }﹩. The plotted curves correspond to stellar inclinations (i): 50° (blue), 60° (red), and 67° (green). Within an assumed mass range of 0.6–0.8 M_⊙, the star is identified as a fast rotator, with its rotation speed constrained between 0.76 and 0.94 of the breakup velocity, depending on the assumed inclination.