The Carnegie Supernova Project I

Spectroscopic analysis of stripped-envelope supernovae

¹ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: max@phys.au.dk
² Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA
³ Carnegie Observatories, Las Campanas Observatory, Casilla 601, La Serena, Chile
⁴ Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
⁵ Department of Physics, Florida State University, 77 Chieftain Way, Tallahassee, FL 32306, USA
⁶ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
⁷ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁸ Instituto de Astrofísica de La Plata (IALP), CONICET, Paseo del Bosque s/n, 1900 La Plata, Argentina
⁹ Facultad de Ciencias Astronómicas y Geofísicas (FCAG), Universidad Nacional de La Plata (UNLP), Paseo del Bosque s/n, 1900 La Plata, Argentina
¹⁰ Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks, Rm 100, Norman, OK 73019, USA
¹¹ Finnish Centre for Astronomy with ESO (FINCA), 20014 University of Turku, Finland
¹² Tuorla Observatory, Department of Physics and Astronomy, 20014 University of Turku, Finland
¹³ DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
¹⁴ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA

Received: 31 October 2022
Accepted: 13 March 2023

Abstract

An analysis leveraging 170 optical spectra of 35 stripped-envelope (SE) core-collapse supernovae (SNe) observed by the Carnegie Supernova Project I and published in a companion paper is presented. Mean template spectra were constructed for the SNe IIb, Ib, and Ic subtypes, and parent ions associated with designated spectral features are identified with the aid of the spectral synthesis code SYNAPPS. Our modeled mean spectra suggest the ∼6150 Å feature in SNe IIb may have an underlying contribution due to silicon, while the same feature in some SNe Ib may have an underlying contribution due to hydrogen. Standard spectral line diagnostics consisting of pseudo-equivalent widths (pEWs) and blue-shifted Doppler velocity were measured for each of the spectral features. Correlation matrices and rolling mean values of both spectral diagnostics were constructed. A principle component analysis (PCA) was applied to various wavelength ranges of the entire dataset and suggests clear separation among the different SE SN subtypes, which follows from trends previously identified in the literature. In addition, our findings reveal the presence of two SNe IIb subtypes, a select number of SNe Ib displaying signatures of weak, high-velocity hydrogen, and a single SN Ic with evidence of weak helium features. Our PCA results can be leveraged to obtain robust subtyping of SE SNe based on a single spectrum taken during the so-called photospheric phase, separating SNe IIb from SNe Ib with ∼80% completion.