Top: observed and modeled extinction curve of BD 134920. The extinction curve by Fitzpatrick (2004), Valencic et al. (2004) and Gordon et al. (2009) is shown with a dashed line, UBV JHK photometrywith filled circles, IUE/FUSE spectra are represented by the grey shaded area, and uncertainties are 1 σ. The model is shown (brown solid line) as well as the contribution of the different dust populations to the extinction (various colored and labeled lines). Bottom: polarisation spectra observed with FORS2 are shown with grey lines, and the and best-fit model with brown solid lines; the filled circles (with 1 σ error bars) are the same data rebinned to a spectral resolution of λ∕Δλ ~ 50.