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tokens: along an almost perfect line in the northwest–southeast direction. The centroids, however, depart from this line at high velocities, especially for the blueshifted gas (≤−8 km s −1 ), although some of the associated positional errors are large. This suggests the presence of a second kinematic component. As shown in Section 4 , this configuration is consistent with the presence of an almost edge-on ionized disk, and a disk wind. 4. Modeling of the H21<italic>α</italic> RRL Similar configurations to the RRL centroid map obtained for MonR2-IRS2 have been observed for MWC349A (Martín-Pintado et al. 2011 ; Báez-Rubio et al. 2013 ; Zhang et al. 2017 ) and MWC922 (Sánchez Contreras et al. 2019 ). This configuration has been modeled assuming that the massive star is surrounded by a (partly) ionized Keplerian disk and an ionized wind. We have thus adopted a similar physical structure to model the H21 α centroid map derived for MonR2-IRS2. The set of input parameters that best fit our ALMA observations is described below (see also Table 1 ). Table 1 Input Parameters of the Best Fit of the MonR2-IRS2 H21 α Data Note. a r is in units of au and angles are measured relative to the polar axis; θ and θ a , are in degrees. In our model, the ionized wind lies inside a double cone with a semi-opening angle of 57° (the neutral disk), while the ionized disk layer is contained within an opening angle of 65 on the surface of the double cone (Figure 4 ). The ionized wind expands radially at a constant velocity, v 0 , while the circumstellar disk rotates following a Keplerian law with the velocity rotation component being added to the expansion velocity of the wind (Martín-Pintado et al. 2011 ; Báez-Rubio et al. 2013 ). The inclination angle is measured from the direction perpendicular to the disk and is −25°. Figure 4. Sketch of the double-cone geometry used for the modeling of MonR2-IRS2 (see also Martín-Pintado et al. 2011 ; Báez-Rubio et al. 2013 ). We have used the non-LTE 3D radiative transfer code MORELI (MOdel for REcombination LInes; Báez-Rubio et al. 2013 ) and the departure coefficients of hydrogen, b n and β n , calculated by Walmsley ( 1990 ). The velocity separation between the H21 α emission peaks (blueshifted and redshifted; Figure 2 ) constrains the central mass of the MonR2-IRS2 source to 15 M ⊙ . This mass corresponds to a B0-type star on the zero-age main sequence, which is consistent with the luminosity of MonR2-IRS2 (∼0.5–1 × 10 4 L ⊙ ; Howard et al. 1994 ). The radial density distribution of electrons within the ionized double cone, N e , follows a r −2 law with an inner radius of 13 au (Table 1 ). We choose a r −2 law because it fits nicely the 1.3, 0.85 and 0.4 mm free–free continuum fluxes of MonR2-IRS2, and it allows us to simultaneously model the disk and the expanding wind in a simple way. The predicted mass-loss rate for MonR2-IRS2 is 2.8 × 10 −7 M ⊙ yr −1 , and the mass of the ionized disk is 2.4 × 10 −5 M ⊙ , a factor ≥10 lower