Helium enrichment during classical nova outbursts

Abstract

Nova outbursts play an important role in the chemical evolution of galaxies, especially they are the main source of synthetic ${}^{13}\mathrm{C}$, ${}^{15}\mathrm{N}$, ${}^{17}\mathrm{O}$ and some radioactive isotopes like ${}^{22}\mathrm{Na}$ and ${}^{26}\mathrm{Al}$. The enrichment of He in nova ejecta indicates that the accreted material may mix with the He-shell (He-mixing). The purpose of this work is to investigate how the He-mixing affects the nova outbursts in a systematic way. We evolved a series of accreting WD models, and found that the mass fraction of H and He in nova ejecta can be influenced by different He-mixing fractions significantly. We also found that both the nova cycle duration and ejected mass increase with the He-mixing fractions. Meanwhile, the nuclear energy production from $p$-$p$ chains decreases with the He-mixing fraction during the nova outbursts, whereas the CNO-cycle increases. The present work can reproduce the chemical abundances in the ejecta of some novae, such as GQ Mus, ASASSN-18fv, HR Del, T Aur and V443 Sct. This implies that the He-mixing process cannot be neglected when studying nova outbursts. This study also develops a He-mixing meter (i.e. $He/H$) that can be used to estimate the He-mixing fraction in classical nova systems.

arXiv comment15 pages, 9 figures, accepted by MNRAS, comments welcome!

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• Mixing fraction in classical novae