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Astron. Astrophys. 361, 1001-1004 (2000)

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Evolution of magnetic field and spin period in accreting neutron stars

K.S. Cheng 1 and C.M. Zhang 1,2,3

1 Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China
2 Department of Physics, Hebei University of Technology, Tianjin-300130, P.R. China
3 Instituto de Física Teórica, Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 São Paulo, Brazil

Received 26 April 2000 / Accepted 7 July 2000


Based on the accretion-induced magnetic field decay model, in which a frozen field and an incompressible fluid are assumed, we obtain the following results: (1) an analytic relation between the magnetic field and spin period, if the fastness parameter of the accretion disk is neglected (The evolutionary tracks of accreting neutron stars in the P-B diagram in our model are different from the equilibrium period lines when the influence of the fastness parameter is taken into account.); (2) the theoretical minimum spin period of an accreting neutron star is [FORMULA] [FORMULA], independent of the accretion rate (X-ray luminosity) but dependent on the total accretion mass, [FORMULA]; however, the minimum magnetic field depends on the accretion rate; (3) the magnetic field strength decreases faster with time than does the period.

Key words: stars: magnetic fields – stars: neutron – stars: rotation

Send offprint requests to: K.S. Cheng

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© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000