Position dependence of integrated line intensities for HCO⁺ 4–3, compared with integrated line intensity profiles from flattened ellipsoidal physical models (Sect. 4.5). Model slices are shown for an HCO⁺ abundance of 1.2  ×  10^-8 (left column) and 6  ×  10^-9 (right column). The viewing angle i varies from 60° (top) to 40° (middle) to 20° (bottom). Values of optical depth at line center through the center of the model, as determined by the ray tracing routine, are for X =  1.2  ×  10^-8: 42, 28, 23 at i = 60,40,20°, respectively; and for X =  6  ×  10^-9: 23, 15, 13 at i = 60,40,20°, respectively.