Constraints to Possible Progenitor Systems of PSR 1831-00

Abstract

Numerical computations were carried out to simulate the evolution of the recently discovered radio pulsar binary PSR 1831-00 with a very low mass function (Porb = 1.81 days, Dewey et al. 1986). These show that the minimum value of the initial mass of the progenitor of the mass-losing secondary is about 1 M⊙. All computed systems with a final period equal to the observed one, and an initial progenitor mass of 1 M⊙ have an age of the order of the Hubble time (∼ 1.3 × 1010years). For a 1.5 M⊙ progenitor of the mass-losing secondary we find that the final (= presently observed) orbital period sets strong constraints to the possible initial system configuration: the binary period should have been such that the 1.5 M⊙ star was just at the onset of the over-all contraction phase (Porb = 0.74 days, XC = 0.05) when it began to fill its Roche-lobe, and the initial mass or the compact mass-accreting star must have been < 0.85 M⊙. (This star was then presumably a white dwarf, which later collapsed due to the accretion). For example, the final period and remnant secondary mass for a system with an initial configuration of 1.5 + 0.8 M⊙ are 1.83 days and 0.20 M⊙, respectively.If one would start out from a more evolved initial state of the 1.5 M⊙ secondary than the end of the overall-contraction phase, the maximum initial mass of the compact object will become drastically smaller and the final remnant mass of the secondary becomes larger than 0.20 M⊙ in all cases.Calculations for a 2.0 M⊙ progenitor of the secondary suggest that if such a progenitor can produce the present system, the initial mass of the accreting primary was at maximum 1.30 M⊙.All the calculations were performed with the inclusion of magnetic braking in so far as the extent of the convective envelope allowed this (see Pylyser & Savonije 1986, in preparation). The effects of the explosion effects due to the accretion induced collapse of the white dwarf were not taken into account.