Stellar gas-pressure fraction
= Stellar gas-pressure fraction
{title2=$\beta=P_{\rm gas}/(P_{\rm gas}+P_{\rm rad})$}
The gas-pressure fraction describes the relative support by an <ideal gas> and <radiation pressure>. For monatomic gas plus equilibrium radiation, it determines the <adiabatic exponents of a monatomic gas-radiation mixture>. Its value at the unperturbed state may be specified, but it generally changes during an isentropic parcel displacement.