2021 Winner: Unburned carbon in the Outer Layers of Type Ia Supernova Ejecta

Project Information
Unburned carbon in the Outer Layers of Type Ia Supernova Ejecta
Physical and Biological Sciences
Physics (Astrophysics) -- Physics 182
I investigate the presence of unburned carbon in the spectra of the early-time epochs of type Ia supernovae (SNe Ia). SNe Ia are thermonuclear explosions of carbon and oxygen rich white dwarfs. The explosion mechanism of SNe Ia is not fully understood, but carbon detected in SNe Ia can give us insight because the carbon detected comes from the star prior the explosion. I include a literature review for a comprehensive understanding of some of the physics behind SNe Ia and previous research on SN Ia focusing on unburned carbon. We use a relational database to examine a sample of 225 SNe with 2516 spectra. I explain our computational method of calculating the equivalent width (EW) of C II λ6580 as a way to distinguish SNe into two groups; Carbon-positive and Carbon-negative. We examine various epochs of the two groups in composite spectra to investigate any correlations and differences with spectral features. We confirm previous claims that at peak luminosity Carbon-positive SNe have a lower Si II λ6355 velocity than Carbon-negative SNe. This can simply be due to incomplete burning offering less kinetic energy per unit mass as the presence of carbon indicates incomplete burning. Our investigation into the nebular epoch shows something else more subtle. In the nebular we saw that both the Carbon-positive and Carbon-negative groups are blueshifted at early times, but the Carbon-negative group is redshifted at nebular epochs while the Carbon-positive group is blueshifted at nebular epochs, hinting at an asymmetrical explosion. This implies there is a more complete burning in the direction opposite of the inner ejecta probed by in nebular spectra. Which implies the difference of velocities and carbon can be dependent on the angle of observation. Further investigation is required for a more robust conclusion.
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  • Rodrigo Angulo (Crown)