ACCRETION AND EVOLUTION OF THE NEUTRON-STAR MAGNETIC-FIELD

The weak magnetic field of many old pulsars entering binary systems st rongly supports the idea of the field decay in those objects. The pres ent paper considers a mechanism for fast field decay associated with a dditional heating of the neutron star during the mass transfer phase. Heating decreases the conductivity of the neutron star crust and may b e responsible for an acceleration of the magnetic field decay if the c urrents maintaining this field are concentrated in the crust. The fiel d strength at the end of the accretion phase depends on both the total amount of the accreted mass, Delta M, and the accretion rate, M. Comp utations have been performed for a wide range of accretion rates and d urations of the accretion phase. The dependence of the field on the ac creted mass can be fitted by a simple power law, B proportional to Del ta M(-gamma) with gamma approximate to 0.8, for relatively high values of Delta M, Delta M> 10(-6) M. yr(-1). The low magnetic field of many pulsars entering binary systems may well be accounted for by this mec hanism.