On the spectrum and nature of the peculiar Type Ia supernova 1991T

A parametrized supernova synthetic-spectrum code is used to study line iden tifications in the photospheric-phase spectra of the peculiar Type Ia SN 19 91T, and to extract some constraints on the composition structure of the ej ected matter. The inferred composition structure is not like that of any hy drodynamical model for Type Ia supernovae. Evidence that SN 1991T was overl uminous for a SN Ia is presented, and it is suggested that this peculiar ev ent was probably a substantially super-Chandrasekhar explosion that resulte d from the merger of two white dwarfs.