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).