The evolution of helium white dwarfs III. On the ages of millisecond pulsar systems

We employed recently computed evolutionary white-dwarf models with helium c ores, supplemented by heavier models with carbon-oxygen cores, in order to investigate the ages of millisecond pulsar systems based on the cooling pro perties of the compact companions. Contrary to the behaviour of more massiv e white dwarfs, the evolutionary speed of low-mass white-dwarf models is su bstantially slowed down by ongoing hydrogen burning. By comparing the cooli ng ages of these models with the spin-down ages of the pulsars for those sy stems for which reasonable information about the compact companions is avai lable, we found good correspondence between both ages. Based on these model s any revisions concerning the temporal evolution of millisecond pulsars do not appear to be necessary.