Orbital phase variation of fitted columns, repeated twice for clarity. Gray data points show the equivalent hydrogen column density, N_H, from continuum fitting the Chandra spectra (right hand y-axis). As discussed in the text, the data points are heavily influenced by systematics (the error bars shown are statistical only). The colored data points show the variation of the Ne neutral column from Ne-edge fitting (left y-axis) and corresponding N_H (right y-axis) derived assuming a Ne:H abundance of 1:11481 as per Wilms et al. (2000). The phases of individual Chandra observations are denoted with colored regions. The dashed lines represent the total equivalent column density of the interstellar medium and of Ne (Xiang et al. 2011).