Intrinsic and extinction colour components in SNeIa and the determination of $R_V$

TL;DR

This paper develops a method to separate intrinsic and extinction colour components in Type Ia supernovae to accurately determine the extinction law parameter Rv, revealing systematic trends and proposing corrections.

Contribution

It introduces a model assuming linear dependence of magnitudes on extinction and a one-dimensional intrinsic colour space, leading to a precise Rv measurement.

Findings

Measured Rv = 2.181 ± 0.117

Identified systematic trends in extinction effects

Proposed corrections to extinction formula

Abstract

The key ingredients in this attempt at separating for each supernova the intrinsic and extinction colour components, and then measuring Rv , are the assumptions of a linearized dependence of magnitudes on the extinction component of colour, a one-dimensional extra-intrinsic colour space (in addition to CaII H&K $\lambda$3945 and Si II $\lambda$4131 contributions, and the absence of correlations between intrinsic and extrinsic variabilities. A consistent solution is found under the previous assumptions, but the observed systematic trends point to a small inadequacy of the extinction formula. Once corrected, all systematic extinction effects can be cancelled by choosing a single scaling of the extinction colour component as well as the appropriate value of Rv = 2.181 $\pm$ 0.117