Using 1991T/1999aa-like Type Ia Supernovae as Standardizable Candles

Jiawen Yang, Lifan Wang, Nicholas Suntzeff, Lei Hu, Lauren Aldoroty, Peter J. Brown, Kevin Krisciunas, Iair Arcavi, Jamison Burke, Lluís Galbany, Daichi Hiramatsu, Griffin Hosseinzadeh, D. Andrew Howell, Curtis McCully, Craig Pellegrino, Stefano Valenti

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


We present the photometry of 16 91T/99aa-like Type Ia Supernovae (SNe Ia) observed by the Las Cumbres Observatory. We also use an additional set of 21 91T/99aa-like SNe Ia and 87 normal SNe Ia from the literature for an analysis of the standardizability of the luminosity of 91T/99aa-like SNe. We find that 91T/99aa-like SNe are 0.2 mag brighter than normal SNe Ia, even when fully corrected by the light-curve shapes and colors. The weighted rms of the 91T/99aa-like SNe (with z CMB > 0.01) Hubble residuals is 0.25 ± 0.03 mag, suggesting that 91T/99aa-like SNe are also excellent relative distance indicators to ±12%. We compare the Hubble residuals with the pseudo-equivalent width (pEW) of Si ii λλ6355 around the date of maximum brightness. We find that there is a broken linear correlation between those two measurements for our sample including both 91T/99aa-like and normal SNe Ia. As the pEW max (Si ii λλ6355) increases, the Hubble residual increases when pEW max (Si ii λλ6355) < 55.6 Å. However, the Hubble residual stays constant beyond this. Given that 91T/99aa-like SNe possess shallower Si ii lines than normal SNe Ia, the linear correlation at pEW max (Si ii λλ6355) < 55.6 Å can account for the overall discrepancy of Hubble residuals derived from the two subgroups. Such a systematic effect needs to be taken into account when using SNe Ia to measure luminosity distances.

Original languageEnglish
Article number83
JournalAstrophysical Journal
Issue number1
StatePublished - 1 Oct 2022


FundersFunder number
Centro Superior de Investigaciones Científicas20215AT016
Mitchell Foundation
Unidad de Excelencia María de Maeztu CEX2020-001058-MAST-1613455
National Science FoundationAST-1911151, AST-1911225
National Aeronautics and Space Administration80NSSC20K0456
Texas A and M UniversityAST-1817099
Ministerio de Ciencia e Innovación
European Social FundPID2020-115253GA-I00, RYC2019-027683-I
Agencia Estatal de Investigación


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