The surface abundances of Red Supergiants at core-collapse

Understand

In the first weeks-to-months of a type II-P supernova (SN), the spectrum formation region is within the hydrogen-rich envelope of the exploding star.

• Optical spectra taken within a few days of the SN explosion, when the photosphere is hot, show features of ionised carbon, nitrogen and oxygen, as well as hydrogen and helium.
• Quantitative analysis of this very early phase may therefore constrain the chemical abundances of the stellar envelope at the point of core-collapse.
• Using existing and new evolutionary calculations for Red Supergiants (RSGs), we show that the predictions for the terminal surface [C/N] ratio is correlated with the initial mass of the progenitor star.