Fractional ion abundances N(X^{+ m}) /N(X) for O iv (blue lines), S iv (green lines) and Si iv (red lines) calculated as a function of different electron number densities using atomic data from the OPEN-ADAS database. The continuous, dotted, dashed and dot-dashed lines indicate a different value of electron number density used to calculate the fractional ion abundances for each ion, as described in the legend.