Dependence of the column density with α_T and β_T. α_T is the angle between the orbital plane of the comet and the direction from the comet to the spacecraft at closet approach (α in Fig. 4). β_T is the angle between the direction of the Sun and the direction from the nucleus to the closest approach projected into the orbital plane (β in Fig. 4 and not to be confused with β the power law). Left panel: normalised column density as a function of α_T (°). Right panel: normalised column density as a function of β_T (°)