The evolutionary status of the white dwarf companion of the binary pulsar PSR J1713+0747

Abstract

Splaver and coworkers have measured the masses of the white dwarf and the neutron star components of the PSR J1713+0747 binary system pair by Shapiro Delay. We attempt to find the original configuration of this system performing a set of binary evolution calculations to simultaneously account for the masses of both stars and the orbital period. We considered initial masses of 1.5 and 1.4 \msun for the normal (donor) and the neutron star, respectively. We assumed two metallicity values (Z = 0.010 and 0.020), and an initial orbital period near 3 days. We assume that the neutron star is only able to retain \lesssim 0.10 of the matter transferred by the donor star. Calculations were performed employing our binary hydro code that handles the mass transfer rate in a fully implicit way together with state-of-the-art physical ingredients, diffusion and a non-grey atmospheres. We compare the structure of the resulting white dwarfs with the characteristic age of PSR J1713+0747 finding a nice agreement with observations by Lundgren et al. especially for the case of a donor star with Z= 0.010. This result indicates that the evolution of this kind of binary system is well understood. The models predict that, due to diffusion, the atmosphere of the white dwarf is an almost hydrogen-pure one. We find that such structures are unable to account for the colours measured by Lundgren et al. within their error bars. Thus, some discrepances in the white dwarf emergent radiation remain to be explained.