Carbon–Oxygen Classical Novae Are Galactic ⁷Li Producers as well as Potential Supernova Ia Progenitors

Abstract

We report on studies of classical nova (CN) explosions where we follow the evolution of thermonuclear runaways (TNRs) on carbon-oxygen (CO) white dwarfs (WDs). We vary both the mass of the WD (from 0.6 M e to 1.35 M e ) and the composition of the accreted material. Our simulations are guided by the results of multidimensional studies of TNRs in WDs, which find that sufficient mixing with WD core material occurs after the TNR is well underway, and levels of enrichment are reached that agree with observations of CN ejecta abundances. We use NOVA (our one-dimensional hydrodynamic code) to accrete solar matter until the TNR is ongoing and then switch to a mixed composition (either 25% WD material and 75% solar or 50% WD material and 50% solar). Because the amount of accreted material is inversely proportional to the initial 12 C abundance, by first accreting solar matter the amount of material taking part in the outburst is larger than in those simulations where we assume a mixed composition from the beginning. Our results show large enrichments of 7 Be in the ejected gases, implying that CO CNe may be responsible for a significant fraction (∼100 M e ) of the 7 Li in the galaxy (∼1000 M e ). Although the ejected gases are enriched in WD material, the WDs in these simulations eject less material than they accrete. We predict that the WD is growing in mass as a consequence of the accretion-outburst-accretion cycle, and CO CNe may be an important channel for SN Ia progenitors.

Measuring the masses of magnetic white dwarfs: a NuSTAR legacy survey

“…Hillman et al 2015), there is a region of the parameter space where M WD grows after successive accretion-nova cycles. While this region was limited to very high-mass WDs in most models, hence did not address the observational discrepancy, more recent hydrodynamical simulations of classical novae by Starrfield et al (2020) suggest that WDs with masses in the range 0.6-1.35 M can grow in mass through accretion-nova cycles. The fact that nova models are seen to contradict one another on the topic of mass growth shows that there is no clear consensus on the matter.…”

Accrete, Accrete, Accrete… Bang! (and repeat): The remarkable Recurrent Novae

“…However, if a large quantity of the WD core material mixes with the accreted material (see, for e.g., [53]) the ejecta mass can, in principle, be larger than the critical (ignition) mass -causing the WD mass to decrease. The most recent theoretical studies of nova eruptions -or H-flashes -agree that the accretion efficiency η over the course of an eruption cycle is > 0 (see, for e.g., [8,23,24,54,55,56,57,58]), i.e. the WD mass increases from one H-flash to the next.…”

“…Yet novae are substantially more numerous, with 50 +31 −23 eruptions every year in the Milky Way [2], 65 +16 −15 yr −1 in the Andromeda Galaxy (M 31) [3], and as many as 300 annually in M 87 [4,5]; compared to ∼1 SN per century per host. Like all explosive transients, novae enrich the ISM; in this case through the production of 7 Li, 13 C, 15 N, and 17 O (e.g., [6,7,8,9]).…”

Hydrodynamic simulations of classical novae outbursts and their evolution to supernova Ia explosions

“…Therefore, we have now used NOVA to study the consequences of TNRs on WDs of various masses using three different compositions (40). In all cases we find that more mass is accreted than ejected and, therefore, the WD is growing in mass.…”