The Absolute Magnitudes of 1991T-like Supernovae <sup>*</sup>
M. M. Phillips, C. Ashall, C. R. Burns, C. Contreras, L. Galbany, P. Hoêflich, E. Y. Hsiao, N. Morrell, P. Nugent, S. A. Uddin, E. Baron, Wendy L. Freedman, Chelsea Harris, K. Krisciunas, Sahana Kumar, Jing Lü, S. E. Persson, Anthony L. Piro, Abigail Polin, Melissa Shahbandeh, M. Stritzinger, N. B. Suntzeff
Abstract
Abstract 1991T-like supernovae are the luminous, slow-declining extreme of the Branch shallow-silicon (SS) subclass of Type Ia supernovae. They are distinguished by extremely weak Ca ii H & K and Si ii λ 6355 and strong Fe iii absorption features in their optical spectra at pre-maximum phases, and have long been suspected to be over-luminous compared to normal Type Ia supernovae. In this paper, the pseudo-equivalent width of the Si ii λ 6355 absorption obtained at light curve phases from ≤ +10 days is combined with the morphology of the i -band light curve to identify a sample of 1991T-like supernovae in the Carnegie Supernova Project II. Hubble diagram residuals show that, at optical as well as near-infrared wavelengths, these events are over-luminous by ∼0.1–0.5 mag with respect to the less extreme Branch SS (1999aa-like) and Branch core-normal supernovae with similar B -band light-curve decline rates.