SN 2012dn is a super-Chandrasekhar mass candidate in a purportedly normal spiral (SAcd) galaxy, and poses a challenge for theories of type Ia supernova diversity.Herewe utilize the fast and highly parametrized spectrum synthesis tool, SYNAPPS, to estimate relative expansion velocities of species inferred from optical spectra obtained with six facilities. As with previous studies of normal SN Ia, we find that both unburned carbon and intermediate-mass elements are spatially coincident within the ejecta near and below 14 000 km s-1. Although the upper limit on SN 2012dn's peak luminosity is comparable to some of the most luminous normal SN Ia, we find a progenitor mass exceeding ~1.6 M⊙ is not strongly favoured by leading merger models since these models do not accurately predict spectroscopic observations of SN 2012dn and more normal events. In addition, a comparison of light curves and host-galaxy masses for a sample of literature and Palomar Transient Factory SN Ia reveals a diverse distribution of SN Ia subtypes where carbon-rich material remains unburned in some instances. Such events include SN 1991T, 1997br, and 1999aa where trace signatures of C III at optical wavelengths are presumably detected.

The nearby Type Ia supernova (SNIa) SN2011fe in M101 (cz = 241kms -1) provides a unique opportunity to study the early evolution of a "normal" SNIa, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN2011fe during its first month beginning 1.2days post-explosion and with an average cadence of 1.8days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000kms-1. This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNeIa. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000kms-1. The fact that some O I is present above C II suggests that SN2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta. © 2012. The American Astronomical Society. All rights reserved..