Reddening law of type Ia supernovae

We use the equivalent width of SiII {lambda}4131 in place of the light curve stretch to account for first-order intrinsic luminosity variability. The resulting empirical spectral reddening law exhibits strong features that are associated with CaII and SiII {lambda}6355.

After applying a correction based on the CaII H&K equivalent width we find a reddening law consistent with a Cardelli extinction law. Using the same input data, we compare this result to synthetic rest-frame UBVRI-like photometry to mimic literature observations.