The Physics of Proto–Neutron Star Winds: Implications forr‐Process Nucleosynthesis

We solve the general-relativistic steady-state eigenvalue problem ofneutrino-driven protoneutron star winds, which immediately follow core-collapsesupernova explosions. We provide velocity, density, temperature, andcomposition profiles and explore the systematics and structures generic to sucha wind for a variety of protoneutron star characteristics. Furthermore, wederive the entropy, dynamical timescale, and neutron-to-seed ratio in thegeneral relativistic framework essential in assessing this site as a candidatefor $r$-process nucleosynthesis. Generally, we find that for a given massoutflow rate ($\dot{M}$), the dynamical timescale of the wind is significantlyshorter than previously thought. We argue against the existence or viability ofa high entropy ($\gtrsim300$ per k$_{B}$ per baryon), long dynamical timescale$r$-process epoch. In support of this conclusion, we model the protoneutronstar cooling phase, calculate nucleosynthetic yields in our steady-stateprofiles, and estimate the integrated mass loss. We find that transonic windsenter a high entropy phase only with very low $\dot{M}$($\lesssim1\times10^{-9}$ M$_\odot$ s$^{-1}$) and extremely long dynamicaltimescale ($\tau_\rho\gtrsim0.5$ seconds). Our results support the possibleexistence of an early $r$-process epoch at modest entropy ($\sim150$) and veryshort dynamical timescale, consistent in our calculations with a very massiveor very compact protoneutron star that contracts rapidly after the precedingsupernova. We explore possible modifications to our models, which might yieldsignificant $r$-process nucleosynthesis generically. Finally, we speculate onthe effect of fallback and shocks on both the wind physics and nucleosynthesis.Comment: 32 pages, aastex, 13 figures, accepted to the Astrophysical Journal; paper revised and various points clarifie