THE CARNEGIE SUPERNOVA PROJECT: INTRINSIC COLORS OF TYPE Ia SUPERNOVAE
2014
ASTROPHYSICAL JOURNAL
DOI
10.1088/0004-637X/789/1/32
We present an updated analysis of the intrinsic colors of Type Ia supernova (SNe Ia) using the latest data release of the Carnegie Supernova Project. We introduce a new light-curve parameter very similar to stretch that is better suited for fast-declining events, and find that these peculiar types can be seen as extensions to the population of "normal" SNe Ia. With a larger number of objects, an updated fit to the Lira relation is presented along with evidence for a dependence on the late-time slope of the B - V light-curves with stretch and color. Using the full wavelength range from u to H band, we place constraints on the reddening law for the sample as a whole and also for individual events/hosts based solely on the observed colors. The photometric data continue to favor low values of R-V, though with large variations from event to event, indicating an intrinsic distribution. We confirm the findings of other groups that there appears to be a correlation between the derived reddening law, R-V, and the color excess, E(B - V), such that larger E(B - V) tends to favor lower R-V. The intrinsic u-band colors show a relatively large scatter that cannot be explained by variations in R-V or by the Goobar power-law for circumstellar dust, but rather is correlated with spectroscopic features of the supernova and is therefore likely due to metallicity effects.