The reddening law of Type Ia Supernovae: separating intrinsic variability from dust using equivalent widths

Understand

We employ 76 type Ia supernovae with optical spectrophotometry within 2.5 days of B-band maximum light obtained by the Nearby Supernova Factory to derive the impact of Si and Ca features on supernovae intrinsic luminosity and determine a dust reddening law.

• We use the equivalent width of Si II {\lambda}4131 in place of light curve stretch to account for first-order intrinsic luminosity variability.
• The resultant empirical spectral reddening law exhibits strong features associated with Ca II and Si II {\lambda}6355.
• After applying a correction based on the Ca II H&K equivalent width we find a reddening law consistent with a Cardelli extinction law.