Abundance stratification in Type Ia Supernovae - II: The rapidly declining, spectroscopically normal SN 2004eo

TL;DR

This paper investigates the abundance stratification in the Type Ia supernova SN 2004eo, revealing how its composition and nucleosynthesis explain its rapid decline and dimness compared to typical supernovae.

Contribution

It provides a detailed spectral analysis of SN 2004eo, showing the distribution of elements and limited nickel production, which is a novel insight into this specific supernova's explosion mechanism.

Findings

Outer ejecta dominated by oxygen and silicon

Limited 56Ni production (~0.43 Msun) explains dimness

Presence of stable Fe-group material in the innermost zone

Abstract

The variation of properties of Type Ia supernovae, the thermonuclear explosions of Chandrasekhar-mass carbon-oxygen white dwarfs, is caused by different nucleosynthetic outcomes of these explosions, which can be traced from the distribution of abundances in the ejecta. The composition stratification of the spectroscopically normal but rapidly declining SN2004eo is studied performing spectrum synthesis of a time-series of spectra obtained before and after maximum, and of one nebular spectrum obtained about eight months later. Early-time spectra indicate that the outer ejecta are dominated by oxygen and silicon, and contain other intermediate-mass elements (IME), implying that the outer part of the star was subject only to partial burning. In the inner part, nuclear statistical equilibrium (NSE) material dominates, but the production of 56Ni was limited to ~0.43 \pm 0.05 Msun. An innermost zone containing ~0.25 Msun of stable Fe-group material is also present. The relatively small amount of NSE material synthesised by SN2004eo explains both the dimness and the rapidly evolving light curve of this SN.