Top: velocity profiles of observed HCO⁺ 4–3 (histogram), compared to those from various models, all at the central spatial position. The profiles from the spherical (1D) model and the infall model follow from an HCO⁺ abundance of 1.5  ×  10^-8, and the abundance for the model used for the flattened model profile is 6  ×  10^-9. Bottom: velocity profiles of observed and modeled H¹³CO⁺, with abundances scaled by a factor 60 with respect to H¹²CO⁺.