The effects of diffusion and winds on the properties of Helium White Dwarfs in Binary Millisecond Pulsars

Abstract

Wide Binary Millisecond Pulsars are composed of a rapidly spinning neutron star and a low-mass white dwarf. An important key to understanding the spin-down evolution of the pulsar is the determination of its age. Under the assumption that the pulsar and white dwarf formed coevally, the age of the pulsar can be inferred by comparing the observed temperature of the cooling white dwarf with evolutionary calculations. The rate of cooling is affected by the composition profile and thickness of the hydrogen-rich envelope. The latter property is largely governed by the evolution of the white-dwarf progenitor during the mass-loss phase of the evolution but is also affected to some degree by stellar winds and chemical diffusion. Based on an extensive analysis of parameter space, we find that self-induced stellar winds are not likely to have a significant effect on the cooling but that diffusion in the envelope can shorten the cooling times in some systems by a significant factor. This effect generally leads to better agreement between cooling and spin-down times.