STAREVOL is a one-dimensional implicit Lagrangian stellar evolution code.

Basic inputs

Nuclear reaction rates are needed to follow the chemical changes inside burning sites, and to determine the production of energy by the nuclear reaction, $\epsilon_{nuc}$, and the energy loss by the neutrino, $\epsilon_{\nu}$. We follow stellar nucleosynthesis with a network including 185 nuclear reactions involving 54 stable and unstable species from $^1$H to $^{37}$Cl. Numerical tables for the nuclear reaction rates were generated through the NetGen web interface¹.

The thermonuclear reaction rates for charged particles are taken either from the NACRE II compilation (Xu et al. 2013) , the NACRE compilation (Angulo et al. 1999) or from Caughlan & Fowler (1988) when NACRE rates are unavailable . For beta-decay, we use rates from Horiguchi et al. (1996). For proton captures on elements more massive than Ne, we follow the rates from Longland et al. (2010) or Illiadis et al. (2001), and neutron capture reaction rates are essentially from Bao et al. (2000).

The screening factors are calculated with the formalism of Mitler (1977) for weak and intermediate screening conditions and Graboske et al. (1973) for strong screening conditions.

Opacities are required to compute the radiative gradient $\nabla_{rad}$ and the energy transport by radiative transfer. We generate opacity tables according to Iglesias & Rogers (1996) using the OPAL website for T>8000 K that account for C and O enrichments. At lower temperature (T<8000 K), we use the atomic and molecular opacities given by Ferguson et al.(2005) and Serenelli et al. (2009).

The equation of state relates the temperature, pressure, and density and thus provides different thermodynamic quantities ($\nabla_{ad}$,c$_P$, ...). In STAREVOL, we follow the formalism developed by Eggleton et al.(1973) and extended by Pols et al.(1995), which is based on the principle of Helmholtz free energy minimization (see Dufour 1999; and Siess et al. 2000, for detailed description and numerical implementation): this accounts for the non-ideal effects of Coulomb interactions and pressure ionization.

The treatment of convection is needed to compute the temperature gradient inside a convective zone. It is based on a classical mixing-length formalism. The boundary between convective and radiative layers is defined with the Schwarzschild criterion. $\alpha_{MLT}$ is specified for each grid and always recovered from solar-calibrated models including the appropriate physics.

In the STAREVOL code, the full set of stellar structure equations is used for the whole star : there is no decoupling between the interior and the atmosphere as in most of the other stellar evolution codes. The surface boundary conditions are treated either assuming a grey atmosphere, or using the so-called Hopf function, $q(\tau)$ that provides a correction to the grey approximation at a given optical depth $\tau$, $T_{\rm eff}$ being the temperature of the equivalent black body and $T(\tau)$ the temperature profile.

For mass loss, we use Reimers (1975) formula (with $\eta_R$=0.5) from the ZAMS up to central helium exhaustion. On the AGB, we adopt the mass-loss prescription of Vassiliadis & Wood (1993).