The Carnegie Supernova Project I. Methods to estimate host-galaxy reddening of stripped-envelope supernovae

We aim to improve upon contemporary methods to estimate host-galaxy reddening of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova Project (CSP-I) SE SN photometry data release, consisting of nearly three dozen objects, is used to identify a minimally reddened sub-sample for each traditionally defined spectroscopic sub-type (i.e., SNe IIb, SNe Ib, SNe Ic). Inspection of the optical and near-infrared (NIR) colors and color evolution of the minimally reddened sub-samples reveals a high degree of homogeneity, particularly between 0 d to +20 d relative to B-band maximum. This motivated the construction of intrinsic color-curve templates, which when compared to the colors of reddened SE SNe, yields an entire suite of optical and NIR color excess measurements. Comparison of optical/optical vs. optical/NIR color excess measurements indicates the majority of the CSP-I SE SNe suffer relatively low amounts of reddening (i.e., E(B-V)_host< 0.20 mag) and we find evidence for different R_V^host values among different SE SN. Fitting the color excess measurements of the seven most reddened (i.e., E(B-V)_host> 0.20 mag) objects with the Fitzpatrick (1999, PASP, 111, 63) reddening law model provides robust estimates of the host visual-extinction A_V^host and R_V^host. In the case of the SE SNe with relatively low amounts of reddening, a preferred value of R_V^host is adopted for each sub-type, resulting in estimates of A_V^host through Fitzpatrick (1999) reddening law model fits to the observed color excess measurements. Our analysis suggests SE SNe reside in galaxies characterized by a range of dust properties. We also find evidence that SNe Ic are more likely to occur in regions characterized by larger R_V^host values compared to SNe IIb/Ib and they also tend to suffer more extinction. The later finding is consistent with work in the literature suggesting SNe Ic tend to occur in regions of on-going star formation.

Based on observations collected at Las Campanas Observatory.