Comparison in flux density and in T_B scales (T_B/F_ν = 482.609 K Jy^-1) between the ¹³CH₃OH(12_1,11–12_0,12)A spectrum extracted at ±006 from the protostar (see Fig. 2: blue- and redshifted emission towards north-west and south-east, respectively) in the direction along the equatorial plane (i.e. disc plane; Lee et al. 2017). The vertical dashed line stands for the systemic V_LSR velocity (+1.7 km s^-1, Lee et al. 2014).