Physics Options

YREC is generally called by two namelists: the “control” namelist, or nml1; and the “physics” namelist, or nml2. This page is a reference that will document various current and deprecated possible commands in the namelist files.

Physics (.nml2)

Constants

YREC does computations in CGS but outputs in solar units.

Parameter	Description
CLSUN	Definition of \(L_\odot\) used for tracks and output
CRSUN	Definition of \(R_\odot\) used for tracks and output

Core fitting options

Parameter	Description
LCORE	If .TRUE., move the central fitting point inward using a Taylor expansion approximation.
FCORE	Factor in mass by which the central fitting point is moved inward.

Gravitational settling & microscopic diffusion

Parameter	Description
LDIFY	Enable gravitational settling of helium.
LDIFZ	Enable gravitational settling of metals.
LDIFLI	Enable gravitational settling of light species.
FGRY	Scaling factor for helium-settling diffusion coefficients (e.g., 0.75 if no rotational mixing).
FGRZ	Scaling factor for metal-settling diffusion coefficients.
DT_GS	Settling solved in multiple timesteps if global timestep < DT_GS * τ(CZ base).
XMIN	Disable diffusion once central hydrogen X < XMIN.
YMIN	Disable diffusion once surface helium Y < YMIN.
GRTOL	Numerical tolerance for diffusion abundance changes.
NITER_GS	Maximum iterations for diffusion abundance solver.
ILAMBDA	Formula for Coulomb logarithm, used in collision integrals; 4 (recommended) is a constant, 2.2.

Numerical convergence options

Parameter	Description
LNEWS	Extrapolate changes from prior step for next step in initial entropy change estimate; can improve convergence.
NITER1	Iterations before SBC (surface boundary condition) is checked.
NITER2	Iterations after SBC check, assumes start of T nuclear burning rates.
NITER3	Iterate between model solution and nuclear burning rates (set to 0 if you encounter convergence difficulties).
NITER4	Iterate betweeen model solution, rotation, and rotationally induced mixing. Set to 0 for models without rotation.
ITDIF1	Iterations between structure equations and rotational mixing (1=none). This is the same as NITER3 unless >1. Recommend 2 for rotational mixing models.
FCORR0	The code predicts corrections to the structure variables, which can initially be overestimated. This is the iteration 1 scale factor by which they are multipled.
FCORRI	This is the increment to the factor for each successive interation, for example it reaches the max of 1 in 8 steps if (0.6,0.05). larger factor = faster convergence, less stable.
HTOLER(1,1)	Convergence tol for log P. If the maximum correction in a given stage anywhere is below this threshold (for all 4 state variables), the run is converged.
HTOLER(2,1)	Convergence tol for log T.
HTOLER(3,1)	Convergence tol for log R.
HTOLER(4,1)	Convergence tol for L/Ltot. Note: all are local
HTOLER(5,1)	If the difference between analytic and numerical derivatives is better than this, iteration is skipped. (5,1) is for P+R
HTOLER(5,2)	If the difference between analytic and numerical derivatives is better than this, iteration is skipped. (5,2) is for T+L

Convective mixing & overshoot

Parameter	Description
LSEMIC	Enable semi-convection.
LOVSTC	Enable core overshoot mixing. Note: unless LOVAD=.TRUE., this is overmixing only, and does not impact the thermal structure
ALPHAC	Core overshoot in pressure scale heights.
LOVMAX	Alternative test (only checked if LOVSTC = .TRUE.) to avoid pathologies in overshoot of small cores.
BETAC	Alternative test - maximum overshoot in fraction of physical size of core
LOVSTE	Enable envelope overshoot.
ALPHAE	Envelope overshoot in pressure scale heights.
LOVSTM	Enable overshoot in intermediate convection zones (recommend not on, needs to be checked).
ALPHAM	Intermediate overshoot (above and below) in pressure scale heights.
TGCUT	Adiabatic convection assumed above this log T.

Equation of state (EOS)

Parameter	Description
LSCV	Use SCV EOS in domain where it is valid and OPAL is not.
LOPALE06	Use OPAL EOS. Note - a simplified Boltzmann/Saha solver, fully ionized at high T, is used when this is disabled, or outside the table.
LNumDeriv	Use numerical derivatives instead of analytic ones (very slow).
LDH	Use Debye–Hückel correction for the Yale EOS.
ETADH0	Lower Debye–Hückel parameter limit.
ETADH1	Upper Debye–Hückel parameter limit.
TSCUT	Threshold above which the default EOS assumes full ionization.

Opacity options

Parameter	Description
LCondOpacP	Use updated conductive opacity tables.
OPTOL	The code generates a 2D surface abundance opacity table, useful for outer CZs and envelope integration. It switches to a 3D/4D solution when x, z differ from it by more than this.
TMOLMIN	Below this log T, use only molecular opacity (if available).
TMOLMAX	Above this log T, use only atomic opacity. Ramp used between TMOLMIN and TMOLMAX.

Nuclear reaction & burning options

Numerics

The numerics of abundance change solutions and thresholds for computing reaction rates. Only TCUT1 is adjusted from default. Do not change without good reason.

Parameter	Description
WEAKSCREENING	Threshold for using weak-screening in reaction rates.
LSNU	Compute solar neutrino fluxes.
TCUT(1)	Temperature threshold for computing \(\epsilon _{\mathrm{nuc}}\). Others are thresholds for progressively more advanced burning stages (Default 6.5, bad for D burning in preMS)
CMIN	Minimum abundance tracked in solver.
ABSTOL	Absolute convergence criterion for abundance changes.
RELTOL	Relative convergence criterion for abundance changes.
KEMMAX	Maximum substeps for abundance integration.

Light-element burning cross-sections

Parameter	Description
LXLI6	Use manually specified p+⁶Li cross-section.
LXLI7	Use manually specified p+⁷Li cross-section.
XSLI6	Value of p+⁶Li cross-section (keV barns).
XSLI7	Value of p+⁷Li cross-section (keV barns).
LXBE91	Toggle p+⁹Be → γ channel.
LXBE92	Toggle p+⁶Li → d channel.
LXBE93	Toggle p+⁶Li → α channel.
XSBE91	Cross-section for p(⁹Be,γ).
XSBE92	Cross-section for p(⁹Be,d).
XSBE93	Cross-section for p(⁹Be,α).

Surface boundary conditions

Parameter	Description
KTTAU	SBC model selector (0=Eddington, 1=Krishnaswamy, 3=Kurucz, 4=Allard).
TRIDT	The code solves for a SBC between 3 models. This is the spacing between 2 of them in Log Teff. The third is a different L at the average Teff.
TRIDL	Spacing between the lower pair and upper point in Log L.

Atmospheric integration

Parameter	Description
ATMERR	Numerical tolerance for atmosphere integration.
ATMMAX	Maximum step size in log τ for atmosphere integrator.
ATMMIN	Minimum step size in log τ for atmosphere integrator.
ATMBEG	Initial step size in log τ for atmosphere integrator.
ATMD0	log10 of starting density at τ = 0 in the atmosphere integrator (may need adjusting for massive stars).

Envelope integrator

Parameter	Description
ENVERR	Numerical tolerance for envelope integration.
ENVMAX	Maximum step size in log P for envelope integrator.
ENVMIN	Minimum step size in log P for envelope integrator.
ENVBEG	Initial step size in log P for envelope integrator.
STOLR0	Required fractional agreement between envelope mass and mass at fitting point.
IMAX	Integrators start with a large step, divide to smaller, and extrapolate to zero. Maximum number of loops to infer integration step size (envelope + atmosphere).
NUSE	Number of prior steps used for extrapolation to zero step size (atm+env).

Spatial tolerances

Parameter	Description
TOL_DM_MIN	Minimum mass spacing (most important for thin outer fitting points).
TOL_DM_MAX	Maximum log mass spacing (most important for stellar cores).
TOL_DL_MAX	Maximum spacing in L/Lsurf (most important for energy generating regions).
TOL_DP_ENV_MAX	Maximum log P spacing in outer CZ (most important for outer layers).
TOL_DP_CZBASE_MAX	Maximum log P spacing at SCZ base.
TOL_DP_CORE_MAX	Maximum log P spacing below SCZ (important between burning, SCZ base).
FLAG_DX	Minimum threshold for preserving discontinuities in X.
FLAG_DZ	Minimum threshold for preserving discontinuities in Z.
TOL_CZBASE_FINE_WIDTH	Width of fine-zoned region at CZ base (0.4 for red giant models).
FLAG_DW	Minimum threshold for preserving Ω discontinuities.

Timestep criteria

Parameter	Description
LTRIST	Restrict timestep during Hertzsprung gap.
TIME_CORE_MIN	Minimum X,Y for using core vs shell burning criteria.
TIME_DX_CORE_TOT	Max absolute ΔX in core H-burning.
TIME_DX_CORE_FRAC	Max fractional ΔX in core H-burning.
TIME_DY_CORE_TOT	Max absolute ΔY/Z in core He-burning (red clump/HB).
TIME_DY_CORE_FRAC	Max fractional ΔY/Z in core He-burning (red clump/HB).
TIME_DX_TOTAL	Max absolute H burned per timestep (post-MS).
TIME_DX_SHELL	Max fractional ΔX in shell H-burning (post-MS).
TIME_DY_TOTAL	Max absolute He burned (AGB).
TIME_DY_SHELL	Max fractional ΔY in He shell.
LSTRUCT_TIME	Restrict timestep based on structural changes - disabled once Lgrav<0 (minimum radius, close to ZAMS).
TIME_DT	Max local ΔT (pre-MS).
TIME_DP	Max local ΔP (pre-MS).
TIME_DR	Max local ΔR (pre-MS).
TIME_DL	Max local ΔL (pre-MS).
TIME_MAX_DT_FRAC	Max fractional timestep change step-to-step.
TIME_DW_MIX	Max ΔΩ per mixing substep (can be more than one per full model step).
TIME_DW_GLOBAL	Max ΔΩ per model.

Rotation

Parameter	Description
LROT	Enable rotation.
LNEW0	Force new SBC each model when rotation enabled. Required for models with rotation, as rotation is held fixed in the solution. LROT = .TRUE. sets this .TRUE.

Rotation & mixing timesteps

Parameter	Description
TIME_DW_GLOBAL	Maximum ΔΩ per model step (replaces DTWIND).
TIME_DW_MIX	Maximum ΔΩ per mixing step (replaces DTDIF).
ITDIF2	Iterations between nuclear burning and rotational mixing (1=none).
DJOK	Numerical tolerance for rotational mixing.

Structural effects of rotation

Parameter	Description
ACFPFT	Fractional accuracy for departures from spherical symmetry (cubed).
ITFP1	Iterations between equipotential shape and effective radius solutions (structural effects of rotation).
ITFP2	Iterations for measuring effective radius given shape parameter (structural effects of rotation).

Initializing rotation

Parameter	Description
LWNEW	Convert non-rotating model to rotating.
WNEW	Uniform angular velocity if LWNEW = TRUE. If star-disk coupling is being used, should be set to the same value as the disk period. Check your units!
LDISK	Enforce disk locking.
TDISK	Disk lifetime in Gyr. 1e5yr = 1e-4 Gyr is the D burning BL. 1e-4 to 1e-2 is the recommended range
PDISK	Disk rotation period (rad/s). 8 days (9.0902e-6) is the observed median period in solar-mass disked stars in star forming regions.

Angular momentum loss & winds

Parameter	Description
LJDOT0	Enable angular momentum loss.
LMWIND	Use Matt et al. 2012 wind model.
AWIND	Wind law selector (V13 (van Saders & Pinsonneault 2013 model), K97 (legacy Krishnamurthi et al. 1997), CUS is custom. PMMA, PMMB, PMMC, PMMD, PMMM are only used if this is set to CUS.).
FK	Scale factor for angular momentum loss. Typically used as a free parameter to reproduce the solar rotation at the solar age.
LROSSBY	Scale the loss rate relative to the Rossby number. Should be used with a saturation threshold (WMAX or WMAXSUN below).
WMAX	Maximum angular velocity (rad/s) for scaling the mass loss rate and magnetic fields in the scaled solar wind. This is over-written if WMAX_SUN is below 1000; the latter expresses WMAX relative to the solar angular velocity.
WMAX_SUN	WMAX expressed in solar Ω units.
PMMSOLP	log P at Teff in solar model (for B-field calibration).
PMMSOLTAU	Solar convective overturn timescale.

Angular momentum transport

Parameter	Description
LINSTB	Include rotationally induced mixing and hydrodynamic AM transport.
LSOLID	Enforce solid-body rotation everywhere. Set true for strongly coupled magnetic models.
WALPCZ	Angular velocity in CZ scales as R^WALPCZ. 0 = solid body -2 = uniform specific angular momentum
IMPJMOD	Global angular momentum coupling settings. 0 = no effect 1 = solid body everywhere 2 = solid body core, decoupled cz 3 = solid body core, coupled at base of CZ rate.
LCODM	Include magnetic diffusion term.
CODM	Magnetic diffusion term for angular momentum transport. 0 = Pure hydro. Nonzero=extra diffusive mechanism. 9e4 matches the solar core rotation constraints.
FW	Global factor for scaling the angular momentum transport diffusion coefficients.
FC	Scale factor for mixing diffusion coefficeints relative to angular momentum. Typicaly calibrated to match Li depletion in a benchmark (cluster stars or the Sun).
IGSF	Toggle for the stability condition used to evaluate the GSF and ABCD instabilties. 1 is recommended.

Starspots

Parameter	Description
LSDEPTH	Control that descreases spot contrast with depth, assuming a constant B. This does not have a dramatic effect on the results.
SPOTF	Starspot filling factor. 0.25 is the active star bound in main sequence stars.
SPOTX	Starspot temperature contrast; only alter if SPOTF > 0. 0.85 is a typical sunspot value.

Rarely used options

Parameter	Description
LTHOUL	Use Thoul formalism for settling.
LTHOULFIT	Use published fit instead of full solution (not recommended).
HTOLER(1,2)	Abort threshold for log P divergence greater than this.
HTOLER(2,2)	Abort threshold for log T divergence greater than this.
HTOLER(3,2)	Abort threshold for log R divergence greater than this.
HTOLER(4,2)	Abort threshold for L/Ltot divergence greater than this.
TENV0	Minimum T for envelope integration. Code stops below this.
TENV1	Maximum T for envelope integration. Code stops above this.
ATMSTP	Max step for atmosphere integrator (LENVG).
ENVSTP	Max step for envelope integrator (LENVG).

Legacy options

Parameter	Description
LEXCOM	Extend tracked isotopes to include D, Li6/7, Be9.
LNEWDIF	Enable updated settling routines.
LNEWNUC	Use new nuclear cross-section format.
LNULOS1	Use Itoh et al. (1996) neutrino loss rates.
LNEWVARS	Use updated variable names for tolerances.
TOL_DX_MAX	Legacy mesh spacing in X.
TOL_DZ_MAX	Legacy mesh spacing in Z.

Experimental options

Parameter	Description
DPENV	Full mixing from center to fractional mass depth.
LADOV	Experimental adiabatic overshoot.
LVFC	Zahn 1991 variable-FC model.
LDIFAD	Treat meridional circulation as diffusion + advection.
LMDOT	Enable experimental mass-loss module.
LSOLWIND	Remove mass loss scaled to solar wind (not implemented).

Unused parameters

Parameter	Description
TCUT(2)	Not used. Former pp-chain equilibrium threshold.
TCUT(3)	Not used. Former CNO-cycle equilibrium threshold.
MCORE	Not used. Obsolete core mesh allocation parameter.
LENVG	Not used. Outer-layer structure calculation after convergence.
ALFA	Not used. Legacy exponent for Kawaler (1988) wind law.