MESA and NuGrid Simulations of Classical Nova Outbursts and Nucleosynthesis

TL;DR

This paper demonstrates the use of MESA and NuGrid tools to model classical nova outbursts and nucleosynthesis, showing good agreement with previous models and exploring the effects of convective boundary mixing and 3He production.

Contribution

It introduces a new implementation of convective boundary mixing in 1D nova models and confirms 3He production in ONe novae with different accretion rates and WD temperatures.

Findings

Convective boundary mixing modeled with exponential diffusion matches traditional pre-mixed models.

3He can be produced in situ in both CO and ONe novae under certain conditions.

A radiative buffer zone forms due to 3He interplay in specific accretion scenarios.

Abstract

Classical novae are the results of surface thermonuclear explosions of hydrogen accreted by white dwarfs (WDs) from their low-mass main-sequence or red-giant 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 3He can be produced in situ in solar-composition envelopes accreted with slow rates (dM/dt < 1e-10 M_sun/yr) by cold (T_WD < 1d7 K) CO WDs, and that convection is triggered by 3He burning before the nova outburst in this case. Here, we confirm this result for ONe novae. Additionally, we find that the interplay between the 3He production and destruction in the solar-composition envelope accreted with an intermediate rate, e.g. dM/dt = 1e-10 M_sun/yr, by the 1.15 M_sun ONe WD with a relatively high initial central temperature, e.g. T_WD = 15e6 K, leads to the formation of a thick radiative buffer zone that separates the bottom of the convective envelope from the WD surface.