Ryan Foley (Harvard-Smithsonian CfA)

Type Ia Supernovae: Standardizable Candles and Crayons

Type Ia supernovae (SNe Ia) are the best cosmological yard sticks available. Measurements of nearby and distant SNe Ia led to the discovery of the accelerating universe and currently provide the best constraints on the nature of dark energy. SNe Ia are precise distance indicators because of a relationship between their peak brightness and light-curve width, making SNe Ia "standardizable candles." We have recently discovered a new relationship between the intrinsic color of the SN and its ejecta velocity. This effect can be explained by additional line blanketing in the blue for the higher-velocity objects. Velocity information provides a way to correct the observed color, making SNe Ia "standardizable crayons." Knowing the intrinsic color of a SN is necessary to determine how much the SN has been reddened, and thus its true distance. Measuring the ejecta velocity of SNe Ia both improves distance estimates for SNe Ia and reduces potential systematic biases. We discuss the implications of this result, including how using this information will improve measurements of cosmological parameters.