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

• Published in: The Astrophysical journal 2022-10, Vol.938 (1), p.83
• Main Authors: Yang, Jiawen, Wang, Lifan, Suntzeff, Nicholas, Hu, Lei, Aldoroty, Lauren, Brown, Peter J., Krisciunas, Kevin, Arcavi, Iair, Burke, Jamison, Galbany, Lluís, Hiramatsu, Daichi, Hosseinzadeh, Griffin, Howell, D. Andrew, McCully, Curtis, Pellegrino, Craig, Valenti, Stefano
• Format: Article
• Language: English
• Subjects: Astrophysics; Candles; Correlation; Luminosity; Subgroups; Supernovae; Type Ia supernovae
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac8c97

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 λλ 6355 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 λλ 6355) increases, the Hubble residual increases when pEW max (Si ii λλ 6355) < 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 λλ 6355) < 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.