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[38.04] On the Spectrum of the Peculiar Type~Ia Supernova 1997br and the Nature of SN~1991T-like Events

D. Branch, K. Hatano (U. Oklahoma), Y. L. Qiu (BAO), E. Baron (U. Oklahoma), F.--K. Thielemann (U. Basel)

In a recent paper (Fisher et~al. 1999, MNRAS, 304, 67), we discussed the optical spectra and nature of the peculiar Type~Ia SN~1991T, and argued that SN~1991T may have been produced by the merger of two white dwarfs, based on its inferred composition structure (co--existence of carbon and ⁵⁶Ni in velocity space) as well as its over--luminosity. Li et~al. (1999, AJ, 117, 2709) now have presented extensive observational data on the peculiar Type~Ia SN~1997br, which closely resembled SN~1991T. In this poster we present some results of a direct analysis of the spectra of SN~1997br using the SYNOW spectrum synthesis code, and further discuss the nature of SN~1991T--like events.

We find no evidence of carbon in the spectra of SN~1997br. The outer edge of the iron core is found to be around 12,500 km~s^-1, compared to 10,000 km~s^-1 in SN~1991T. Therefore we concur with Li et al. (1999) that SN~1997br was a slightly more powerful version of SN~1991T. The issues of whether or not SN~1991T--like events form a discrete subgroup of SNe~Ia, and the extent to which the spectra of SN~1991T--like events could be consistent with standard delayed--detonation hydrodynamical models, are discussed.