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 λ6355 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 λ6355 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.
@article{arxiv.2209.08031,
title = {The Absolute Magnitudes of 1991T-like Supernovae},
author = {M. M. Phillips and C. Ashall and Christopher R. Burns and Carlos Contreras and L. Galbany and P. Hoeflich and E. Y. Hsiao and Nidia Morrell and Peter Nugent and Syed A. Uddin and E. Baron and Wendy L. Freedman and Chelsea E. Harris and Kevin Krisciunas and S. Kumar and J. Lu and S. E. Persson and Anthony L. Piro and Abigail Polin and Shahbandeh and M. and Maximilian Stritzinger and Nicholas B. Suntzeff},
journal= {arXiv preprint arXiv:2209.08031},
year = {2022}
}