const¶

Status: active in the ./mk mesa build.

Purpose: expose MESA const_def scalar real constants in Python so examples, tests, and solver code use the same CGS values as the linked MESA build.

Fast start¶

from pyfortmesa import mesa

constants = mesa.constants()

T = 1.0e7
Prad = constants["crad"] * T**4 / 3.0
print(Prad)

Public API¶

`mesa.constants()`¶

Signature:

mesa.constants() -> dict[str, float]

Inputs: none.

Returns: a dictionary of scalar real(dp), parameter constants from MESA const_def. Values use the MESA names and cgs/MESA units.

key	units	meaning
`pi`	dimensionless	pi
`pi2`	dimensionless	`pi*pi`
`pi4`	dimensionless	`4*pi`
`eulercon`	dimensionless	Euler-Mascheroni constant
`eulernum`	dimensionless	base of natural logarithms
`ln2`	dimensionless	`log(2)`
`ln3`	dimensionless	`log(3)`
`lnPi`	dimensionless	`log(pi)`
`ln10`	dimensionless	`log(10)`
`iln10`	dimensionless	`1/log(10)`
`a2rad`	`rad deg^-1`	degrees to radians conversion
`rad2a`	`deg rad^-1`	radians to degrees conversion
`one_third`	dimensionless	`1/3`
`two_thirds`	dimensionless	`2/3`
`four_thirds`	dimensionless	`4/3`
`five_thirds`	dimensionless	`5/3`
`one_sixth`	dimensionless	`1/6`
`four_thirds_pi`	dimensionless	`4*pi/3`
`ln4pi3`	dimensionless	`log(4*pi/3)`
`two_13`	dimensionless	`2^(1/3)`
`four_13`	dimensionless	`4^(1/3)`
`sqrt2`	dimensionless	`sqrt(2)`
`sqrt_2_div_3`	dimensionless	`sqrt(2/3)`
`avo`	`mol^-1`	Avogadro constant
`amu`	`g`	atomic mass unit
`clight`	`cm s^-1`	speed of light in vacuum
`qe`	`esu`	elementary charge
`kerg`	`erg K^-1`	Boltzmann constant
`boltzm`	`erg K^-1`	Boltzmann constant alias
`planck_h`	`erg s`	Planck constant
`hbar`	`erg s`	reduced Planck constant
`cgas`	`erg K^-1 mol^-1`	ideal gas constant
`ev2erg`	`erg eV^-1`	electron-volt to erg conversion
`mev_to_ergs`	`erg MeV^-1`	MeV to erg conversion
`mev_amu`	`erg g^-1`	MeV per amu to specific energy conversion
`mev2gr`	`g MeV^-1`	MeV to mass conversion
`Qconv`	`erg mol^-1 MeV^-1`	MeV per particle to erg per mole conversion
`kev`	`eV K^-1`	temperature to electron-volt conversion
`boltz_sigma`	`erg cm^-2 s^-1 K^-4`	Stefan-Boltzmann constant
`crad`	`erg cm^-3 K^-4`	radiation density constant `a`; `Prad = cradT*4/3`
`au`	`cm`	astronomical unit
`pc`	`cm`	parsec
`dayyer`	`day yr^-1`	days per Julian year
`secday`	`s day^-1`	seconds per day
`secyer`	`s yr^-1`	seconds per Julian year
`ly`	`cm`	light year
`mn`	`g`	neutron mass
`mp`	`g`	proton mass
`me`	`g`	electron mass
`rbohr`	`cm`	Bohr radius
`fine`	dimensionless	fine-structure constant
`hion`	`eV`	Rydberg ionization energy
`sige`	`cm^2`	Thomson cross section
`weinberg_theta`	dimensionless	`sin^2(theta_weinberg)`
`num_neu_fam`	dimensionless	number of neutrino families
`standard_cgrav`	`cm^3 g^-1 s^-2`	gravitational constant
`mu_sun`	`cm^3 s^-2`	solar gravitational parameter
`mu_earth`	`cm^3 s^-2`	Earth gravitational parameter
`mu_jupiter`	`cm^3 s^-2`	Jupiter gravitational parameter
`agesun`	`yr`	solar age
`Msun`	`g`	solar gravitational mass
`Rsun`	`cm`	solar radius
`Lsun`	`erg s^-1`	solar luminosity
`Teffsun`	`K`	solar effective temperature
`loggsun`	`log10(cm s^-2)`	solar surface gravity log
`mbolsun`	`mag`	solar bolometric magnitude
`m_earth`	`g`	Earth mass
`r_earth`	`cm`	Earth equatorial radius
`r_earth_polar`	`cm`	Earth polar radius
`m_jupiter`	`g`	Jupiter mass
`r_jupiter`	`cm`	Jupiter equatorial radius
`r_jupiter_polar`	`cm`	Jupiter polar radius
`semimajor_axis_jupiter`	`cm`	Jupiter semimajor axis
`arg_not_provided`	sentinel	MESA omitted-argument sentinel
`missing_value`	sentinel	alias for `arg_not_provided`

Example:

import numpy as np

from pyfortmesa import mesa

constants = mesa.constants()
eos = mesa.Eos()
mix = mesa.composition({"h1": 0.70, "he4": 0.28, "c12": 0.02})

T = 1.0e7
rho = 1.0e2
out = eos.dt_full(T=T, Rho=rho, comp=mix)

Pgas = np.exp(out["results"]["lnPgas"])
Prad = constants["crad"] * T**4 / 3.0
Ptot = Pgas + Prad

Source mapping¶

$MESA_DIR/const/public/const_def.f90
src/pyfortmesa/fortran/const/mesa_const_public.f90
src/pyfortmesa/mesa.py
src/pyfortmesa/mesa_support.py

Fortran wrapper:

mesa_const_values

Python output order is defined by MESA_CONSTANT_NAMES in src/pyfortmesa/mesa_support.py. The Fortran vector order must match that tuple.

Common mistakes¶

crad is the radiation density constant a, not radiation pressure itself. Use Prad = crad*T**4/3.
MESA eos output lnPgas is gas pressure. Add Prad yourself when you want total pressure.
All physical constants returned here use cgs/MESA units.

Not included¶

MESA item	Reason
precision kind parameters such as `sp`, `dp`, `qp`, `i1`, `i2`, `i4`, `i8`	Compile-time Fortran kind tags, not runtime physical constants.
`strlen` and `max_extra_inlists`	Fortran/module configuration integers, not scalar real constants.
runtime path/cache variables such as `mesa_dir` and `mesa_caches_dir`	Mutable module state; use environment helpers instead.
mixing-type integer enums	Star/mesh classification constants, not needed by the current const/chem/eos/kap wrapper surface.