Lifan Wang
Texas A&M University
Abstract:
I will discuss recent results from our efforts to probe in great detail the geometric structure of SNIa, and to apply SNIa as cosmological probes using the CMAGIC method. Spectropolarimetry of Type Ia supernovae (SNIa) show that the degree of polarization of SNIa is typically below 0.3% in the continuum but can be as large as 1-2% across some strong P-Cygni lines. The degree of polarization across the Si II 635.5 nm is found to be correlated to the brightness of the Type Ia supernovae. The polarization data reveals a geometric structure in which the center of the SN ejecta are typically spherically symmetric but with layers above about 10,000 km/sec highly aspherical. The asphericity at the outer, high velocity layers can not be explained by a smooth geometric structure and shows considerable lumpiness in chemical distributions. The smooth central zone is evidence in favor of delayed-detonation models. The lumpiness in the outside, however, is not easily explained by any existing models of SNIa. I will also discuss CMAGIC studies of nearby SNe which results in significantly improved SN distance estimates. The analysis does not confirm the existence of a local Hubble bubble at redshift below about 7,400 km/sec.