Evolution of low mass close binary systems with a neutron star: its dependence with the initial neutron star mass

DE VITO, M. A.; BENVENUTO, O. G.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Wiley InterScience

Año: 2010 vol. 401 p. 2552 - 2560

0035-8711

We  construct  a set  of  binary  evolutionary  sequences for  systemscomposed by  a normal, solar  composition, donor star together  with a neutron star. We consider a variety of masses for each star as well as for the initial orbital period corresponding to systems that evolve to ultra - compact or millisecond pulsar - helium white dwarfpairs. Specifically,  we select  a set of  donor star masses  of 0.50,0.65,  0.80, 1.00,  1.25,  1.50,  1.75, 2.00,  2.25,  2.50, 3.00,  and3.50 M_sun, whereas for the accreting neutron star we consider initial masses values  of 0.8,  1.0, 1.2, and  1.4 M_sun. Because  the minimum mass for a proto - neutron  star is approximately 0.9 M_sun, the value of  0.8 M_sun  was selected  in  order to  cover  the  whole range of possible initial neutron star masses. The  considered initial orbital period interval ranges from 0.5 to 12 days.It is found  that the evolution of systems,  with fixed initial valuesfor the orbital period and the  mass of the normal donor star, heavilydepends upon the mass of the  neutron star. In some cases, varying the initial value of the neutron star mass, we obtain evolved configurations  ranging from ultra - compact to widely separatedobjects.We also  analyse the dependence of  the final orbital  period with the mass of the white dwarf.  In agreement with previous expectations, our calculations  show that  the final  orbital period - white dwarf mass relation is fairly insensitive to the initial neutron star mass value. A new  period - mass relation based on our  own calculations is proposed,  which is  in  good agreement  with period - mass relations available in the literature.As consequence of considering a  set of values for the initial neutronstar  mass, these  models  allow finding  different plausible  initialconfigurations  (donor and neutron star masses  and orbital period interval) for some of the best observed binary systems of the kind we are interested in here. We  apply our calculations to analyse the case of PSR J0437-4715, showing that there is more than one  possible set of initial parameters (masses, period  and the fraction beta of matter accreted by the neutron star) for this particular system.