Hubble Space Telescope Observations of Millisecond Pulsar Companions: Constraints on Evolution

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Abstract
In observations of six binary millisecond pulsars with the Hubble Space Telescope, we have discovered white dwarf companions to PSRs J0034-0534, J1022+1001, J1713+0747, and J2019+2425 and improved photometry on PSRs J1640+2224 and J2145-0750. Three of the white dwarfs are among the coolest and oldest known. We have determined that the masses for the helium companions are consistent with the expectation based on the core mass of a progenitor that filled its Roche lobe. The cooling times for many of the white dwarfs are much less than the characteristic spin-down times, implying that the spin period at the end of the accretion stage was close to the current period. The initial spin periods calculated are used to place limits on the accretion rate at the end of the low-mass X-ray binary phase. The accretion rates are found to be over an order of magnitude less than the Eddington rate.