We report on photometric and spectroscopic observations of white dwarf companions to four binary radio millisecond pulsars , leading to the discovery of companions to PSRs J0614 - 3329 , J1231 - 1411 and J2017+0603 .
We place limits on the brightness of the companion to PSR J0613 - 0200 .
Optical spectroscopy of the companion to PSR J0614 - 3329 identifies it as a DA type white dwarf with a temperature of T _ { \mathrm { eff } } = 6460 \pm 80 K , a surface gravity \log g = 7.0 \pm 0.2 cgs and a mass of M _ { \mathrm { WD } } = 0.24 \pm 0.04 M _ { \odot } .
We find that the distance to PSR J0614 - 3329 is smaller than previously estimated , removing the need for the pulsar to have an unrealistically high \gamma -ray efficiency .
Comparing the photometry with predictions from white dwarf cooling models allows us to estimate temperatures and cooling ages of the companions to PSRs J0613 - 0200 , J1231 - 1411 and J2017+0603 .
We find that the white dwarfs in these systems are cool T _ { \mathrm { eff } } < 4000 K and old \ga 5 Gyr .
Thin Hydrogen envelopes are required for these white dwarfs to cool to the observed temperatures , and we suggest that besides Hydrogen shell flashes , irradiation driven mass loss by the pulsar may have been important .