The Origin of the Elements Revealed by Nebular-Phase Supernovae

by Stan Barmentloo (Stockholm University)

Wednesday 2 Sept 2026, 13:30 → 14:30 Europe/Stockholm

FC 61 (AlbaNova Main Building)

Supernovae (SNe) are the explosive deaths of the most massive stars in the universe. In their cores, these stars fused primordial H and He into heavier elements up to the iron peak. In the explosion, these elements are ejected and returned to the ISM, making SNe one of the prime locations for chemical enrichment in the universe. Despite their importance, a lot of open questions remain as to which types of stars produce which types of SNe, as well as which types of supernovae produce which elements in what amounts.

In this seminar, I will present the work on SNe that I did in the past four years. The main focus of each of these works is to learn something about the star that exploded and the elements it produced, by studying the spectral evolution of the star a few hundred days after explosion, during the so-called nebular phase. In particular, the first two works study spectral emission lines of nitrogen and carbon and what they can tell us about the SN ejecta, and what we learned is then applied to a sample of observed SNe. Among other things, I show that nitrogen lines can be used as a diagnostic for the SN progenitor mass, and that carbon masses in some observed SNe are lower than expected from stellar evolution models. In my third and final thesis work, I shift gears a bit to study line formation in the NIR and MIR wavelength ranges, and I show how one can infer masses of elements such as Cl, Ar and Ni from a single nebular phase JWST spectrum of the Type Ic SN 2024aecx.