The relativistic pulsar-white dwarf binary PSR J1738+0333 - I. Mass determination and evolutionary history

PSR J1738+0333 is one of the four millisecond pulsars known to be orbited by a white dwarf companion bright enough for optical spectroscopy. Of these, it has the shortest orbital period, making it especially interesting for a range of astrophysical and gravity related questions. We present a spectroscopic and photometric study of the white dwarf companion and infer its radial velocity curve, effective temperature, surface gravity and luminosity. We find that the white dwarf has properties consistent with those of low-mass white dwarfs with thick hydrogen envelopes, and use the corresponding mass-radius relation to infer its mass; MWD = 0.181 +0.007 −0.005 M. Combined with the mass ratio q = 8.1 ± 0.2 inferred from the radial velocities and the precise pulsar timing ephemeris, the neutron star mass is constrained to MPSR = 1.47 +0.07 −0.06 M.