RADIAL PULSATIONS AND STABILITY OF PROTONEUTRON STARS

Radial pulsations of newborn neutron stars (protoneutron stars) are st udied for a range of internal temperatures and entropies per baryon pr edicted by the existing numerical simulations. Protoneutron star model s are constructed using a realistic equation of state of hot dense mat ter, and under various assumptions concerning stellar interior (large trapped lepton number, zero trapped lepton number, isentropic, isother mal). Under prevailing conditions, linear oscillations of a protoneutr on star can be treated as adiabatic, and evolutionary effects can be n eglected on dynamic timescale. The dynamic behavior is governed by the adiabatic index, which in turn depends on the physical state of the s tellar interior. The eigenfrequencies of the lowest radial modes of li near, adiabatic pulsations are calculated. Stability of protoneutron s tars with respect to small radial perturbations is studied, and the va lidity of the static stability criteria is discussed.