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

Evolution of magnetic field and spin period in accreting neutron stars

K.S. Cheng ¹ and C.M. Zhang <sup>1,2,3

1</sup> 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

Abstract

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 , independent of the accretion rate (X-ray luminosity) but dependent on the total accretion mass, ; 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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Contents

• 1. Introduction
• 2. Models
  • 2.1. Spin evolution with a constant fastness parameter
  • 2.2. Spin evolution with a non-constant fastness parameter
• 3. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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