MESA and NuGrid simulations of classical novae: CO and ONe nova nucleosynthesis

Abstract

Classical novae are the results of surface thermonuclear explosions of hydrogen accreted by white dwarfs (WDs) from their low-mass main-sequence or redgiant binary companions. Chemical composition analysis of their ejecta shows that nova outbursts occur on both carbon-oxygen (CO) and more massive oxygen-neon (ONe) WDs, and that there is cross-boundary mixing between the accreted envelope and underlying WD. We demonstrate that the state-of-the-art stellar evolution code MESA and post-processing nucleosynthesis tools of NuGrid can successfully be used for modeling of CO and ONe nova outbursts and nucleosynthesis. The convective boundary mixing (CBM) in our 1D numerical simulations is implemented using a diffusion coefficient that is exponentially decreasing with a distance below the bottom of the convective envelope. We show that this prescription produces maximum temperature evolution profiles and nucleosynthesis yields in good agreement with those obtained using the commonly adopted 1D nova model in which the CBM is mimicked by assuming that the accreted envelope has been pre-mixed with WD's material. In a previous paper, we have found that 3 He can be produced in situ in solar-composition envelopes accreted with slow rates (Ṁ < 10 −10 M ⊙ /yr) by cold (T WD < 10 7 K) CO WDs, and that convection is triggered by 3 He burning before the nova outburst in this case. Here, we confirm this result for ONe novae. Additionally, we find that the interplay between the 3 He production and destruction in the solar-composition envelope accreted with an intermediate rate, e.g.Ṁ = 10 −10 M ⊙ /yr, by the 1.15 M ⊙ ONe WD with a relatively high initial central temperature, e.g. T WD = 15 ×10 6 K, leads to the formation of a thick radiative buffer zone that separates the bottom of the convective envelope from the WD surface.

Three New Low-Energy Resonances in theNe22(p,γ)NaCavanna1, Depalo2, Aliotta3 et al. 2015Phys. Rev. Lett.6255801View full textAdd to dashboardCite

“…The 22 Neðp; γÞ 23 Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between 20 Ne and 27 Al in asymptotic giant branch stars and novae.…”

“…This cycle affects the synthesis of the elements between 20 Ne and 27 Al in asymptotic giant branch stars and novae. The 22 Neðp; γÞ 23 Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400 keV, only upper limits exist in the literature for the resonance strengths.…”

“…For an oxygenneon nova, the uncertainty on the 22 Neðp; γÞ 23 Na reaction rate leads to 6 orders of magnitude uncertainty on the 22 Ne yield [22]. For a carbon-oxygen nova, 22 Neðp; γÞ 23 Na was found to affect the abundances of elements between neon and aluminum [22]. As a consequence, there is a call for a more precise 22 Neðp; γÞ 23 Na thermonuclear reaction rate [23].…”

The AMBRE project: a study of Li evolution in the Galactic thin and thick discs

“…The second reason is related to a a well known, but rarely mentioned, problem with nova nucleosynthesis. In all nova models, even if Li is made in substantial amounts, there is invariably an even more important overproduction of the minor CNO isotopes ( 13 C, 15 N and 17 O), for example, José & Hernanz (1998), Denissenkov et al (2014). This is valid both for CO and ONe novae and is a serious handicap for novae as major Li sources: if one assumes that their theoretical yields are approximately constant during galactic evolution, then the minor CNO isotopes would be found largely overproduced, as noticed in José & Hernanz (1998).…”

Hybrid C–O–Ne white dwarfs as progenitors of Type Ia supernovae: dependence on Urca process and mixing assumptions

“…We employ the same MESA equation of state, opacities and reaction rates as in the work of Denissenkov et al (2013). Our nuclear network is similar to the largest one (nova.net) with 77 isotopes from H to 40 Ca coupled by 442 reactions that was used by Denissenkov et al (2014) to prepare WD models for their simulations of ONe nova outbursts, except that it has been extended to 87 isotopes and 500 reactions to include the MESA electron capture network and a new Urca network that become important at very high densities. The Urca network makes use of the well resolved tables of reaction and neutrino-loss rates for Urca pairs with atomic numbers A = 23, 25 and 27 calculated by Toki et al (2013).…”