Carnegie Supernova Project: Classification of Type Ia Supernovae
Abstract
We use the spectroscopy and homogeneous photometry of 97 Type Ia supernovae (SNe Ia) obtained by the Carnegie Supernova Project as well as a subset of 36 SNe Ia presented by Zheng et al. to examine maximumlight correlations in a fourdimensional (4D) parameter space: Bband absolute magnitude, M_{B}, Si ii λ6355 velocity, ${v}_{\mathrm{Si}{\rm\small{II}}}$ , and Si ii pseudoequivalent widths pEW(Si ii λ6355) and pEW(Si ii λ5972). It is shown using Gaussian mixture models (GMMs) that the original four groups in the Branch diagram are welldefined and robust in this parameterization. We find three continuous groups that describe the behavior of our sample in [M_{B}, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] space. Extending the GMM into the full 4D space yields a grouping system that only slightly alters group definitions in the [M_{B}, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] projection, showing that most of the clustering information in [M_{B}, ${v}_{\mathrm{Si}{\rm\small{II}}}$ ] is already contained in the 2D GMM groupings. However, the full 4D space does divide group membership for faster objects between corenormal and broadline objects in the Branch diagram. A significant correlation between M_{B} and pseudoequivalent width (Si ii λ5972) is found, which implies that Branch group membership can be wellconstrained by spectroscopic quantities alone. In general, we find that higherdimensional GMMs reduce the uncertainty of group membership for objects between the originally defined Branch groups. We also find that the broadline Branch group becomes nearly distinct with the inclusion of ${v}_{\mathrm{Si}{\rm\small{II}}}$ , indicating that this subclass of SNe Ia may be somehow different from the other groups.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 2020
 DOI:
 10.3847/15384357/abafa2
 arXiv:
 arXiv:2008.07636
 Bibcode:
 2020ApJ...901..154B
 Keywords:

 Type Ia supernovae;
 1728;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 26 pages, 19 figures, ApJ, in press