The evolution of low-mass, close binary systems with a neutron star component: a detailed grid

Abstract

In close binary systems composed of a normal, donor star and an accreting\nneutron star, the amount of material received by the accreting component is, so\nfar, a real intrigue. In the literature there are available models that link\nthe accretion disk surrounding the neutron star with the amount of material it\nreceives, but there is no model linking the amount of matter lost by the donor\nstar to that falling onto the neutron star.\n In this paper we explore the evolutionary response of these close binary\nsystems when we vary the amount of material accreted by the neutron star. We\nconsider a parameter \\beta, which represents the fraction of material lost by\nthe normal star that can be accreted by the neutron star. \\beta is considered\nas constant throughout evolution. We have computed the evolution of a set of\nmodels considering initial donor star masses (in solar units) between 0.5 and\n3.50, initial orbital periods (in days) between 0.175 and 12, initial masses of\nneutron stars (in solar units) of 0.80, 1.00, 1.20 and 1.40 and several values\nof beta. We assumed solar abundances. These systems evolve to ultracompact or\nto open binary systems, many of which form low mass helium white dwarfs. We\npresent a grid of calculations and analyze how these results are affected upon\nchanges in the value of \\beta. We find a weak dependence of the final donor\nstar mass with respect to \\beta. In most cases this is also true for the final\norbital period. The most sensitive quantity is the final mass of the accreting\nneutron star.\n As we do not know the initial mass and rotation rate of the neutron star of\nany system, we find that performing evolutionary studies is not helpful for\ndetermining \\beta.\n