The surface abundances of Red Supergiants at core-collapse. (arXiv:1811.04087v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Davies_B/0/1/0/all/0/1">Ben Davies</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dessart_L/0/1/0/all/0/1">Luc Dessart</a>
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.
Specifically, a star with an initial mass above 20M$_{odot}$ exploding in the
RSG phase should have an unequivocal signal of a low [C/N] abundance.
Furthermore, we show that the model predictions are relatively insensitive to
uncertainties in the treatment of convective mixing. Although there is a
dependence on initial rotation, this can be dealt with in a probabilistic sense
by convolving the model predictions with the observed distribution of stellar
rotation rates. Using numerical experiments, we present a strategy for using
very early-time spectroscopy to determine the upper limit to the progenitor
mass distribution for type II-P SNe.
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.
Specifically, a star with an initial mass above 20M$_{odot}$ exploding in the
RSG phase should have an unequivocal signal of a low [C/N] abundance.
Furthermore, we show that the model predictions are relatively insensitive to
uncertainties in the treatment of convective mixing. Although there is a
dependence on initial rotation, this can be dealt with in a probabilistic sense
by convolving the model predictions with the observed distribution of stellar
rotation rates. Using numerical experiments, we present a strategy for using
very early-time spectroscopy to determine the upper limit to the progenitor
mass distribution for type II-P SNe.
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