17 December 2009

Speaker: Ryan Foley (CfA / Clay Fellow)

Title: Clay Fellowship Lecture:
Type Ia Supernovae are NOT Standard Candles (but Dark Energy Still Exists)

Abstract:Type Ia Supernovae (SNe Ia) have a relatively low scatter in their peak luminosity. This scatter is further reduced by an empirical relationship between an object's peak luminosity and the width of its light curve. This relationship is key to using SNe Ia as precise distance indicators, allowing us to measure the distance to high-z SNe, which in turn has constrained cosmological parameters and led to the discovery of the accelerating universe. Recently, SN cosmology has transitioned from being limited by the number of SNe to being limited by systematics. I will present results from the ESSENCE and SDSS-II SN surveys which indicate that dark energy is consistent with a cosmological constant, but systematics are limiting precise measurements. In particular, our understanding of extragalactic dust and the UV properties of SNe Ia are the largest systematic effects. I will show progress in understanding these effects by increased knowledge of SN physics through recent observations. I will also discuss deviations from the luminosity-width relation, what they can tell us about SN physics, and how they can affect the measurement of cosmological parameters. Finally, I will discuss the Pan-STARRS survey, a new, ambitious project that will discover thousands of SNe over the next three years.

Video of the Presentation (Talks can be viewed with RealPlayer. Free download is available from www.real.com )