Comparison of column densities for HCO⁺ (top) and N₂H⁺ (bottom) for models with varying SP flux and very strong X-ray emission. For all models the low CR ionization rates are used. Shown are the reference model with normal X-rays (black, CL_XN), the model with the typical SP flux (blue, CL_XN_SP) and models with a factor of ten higher (purple, CL_XN_SPH) and factor of ten lower (red, CL_XN_SPL) SP flux. The dashed black line shows the model with L_X = 3 × 10³¹ erg s^-1 and no SPs. The grey shaded area marks a difference of a factor of three in the column densities relative to the reference model CL_XN.