Fundamental Constants
Fundamental constants are defined in constants/fundamental_constants.H
.
This file contains physical constants and unit conversion factors, such as
Boltzmann’s constant, write_fundamental_constants.py
.
All constant values are obtained from scipy.constants
to ensure consistency
between Microphysics
and pynucastro
, the latter is used for
generating the reaction networks used by Microphysics
.
There are two exceptions:
Constants under the
Legacy
namespace represent outdated values historically used in networks such asaprox13
,aprox19
, andaprox21
. These constants are retained for backward compatibility and should NOT be used in other places.Newton’s gravitational constant continues to use an older value to preserve hydrostatic equilibrium in existing initial models used by
Castro
.
Note
The consistency of physical constants between pynucastro
and
Microphysics
is particularly important when using inverse rates derived
from detailed balance. Discrepancies in constant values can affect the
agreement between mass fractions obtained from direct integration and those
computed from nuclear statistical equilibrium (NSE).
This a subtle point, but important when using NSE evolution mode
(i.e., when compiled with USE_NSE_NET=TRUE
and USE_NSE_TABLE=TRUE
).
See NSE for more details.