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L. Burderi (Osservatorio Astronomico di Roma)
Accurate timing measures demonstrate that, in most cases, the masses of the companions of the low magnetic field, millisecond binary pulsars are below 0.3 solar masses. Orbital evolution calculations show that, when the companion was filling its Roche lobe, about one solar mass was transferred at stable sub-Eddington rates. However several observational evidences indicates that the amount of mass effectively accreted is well below this amount. Observations of low mass X-ray binaries indicate that during this phase the accretion process that spins-up the neutron star is mediated by a virialized accretion disc. In this case we demonstrate that the propeller mechanism by a low magnetic field neutron star is ineffective in ejecting more than one third of the total transferred mass. We show that the prompt switch-on of a millisecond radio pulsar can eject a substantial fraction of the transferred mass, limiting the amount of mass accreted.
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