EDP Sciences
Free access
Issue
A&A
Volume 416, Number 3, March IV 2004
Page(s) 1013 - 1022
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20034387


A&A 416, 1013-1022 (2004)
DOI: 10.1051/0004-6361:20034387

Hyperon softening of the EOS of dense matter and the spin evolution of isolated neutron stars

J. L. Zdunik1, P. Haensel1, 2, E. Gourgoulhon2 and M. Bejger1

1  N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland
    e-mail: bejger@camk.edu.pl
2  LUTH, UMR 8102 du CNRS, Observatoire de Paris, 92195 Meudon Cedex, France
    e-mail: haensel@camk.edu.pl;Eric.Gourgoulhon@obspm.fr

(Received 24 September 2003 / Accepted 12 November 2003)

Abstract
The effect of the hyperon softening of the equation of state (EOS) of dense matter on the spin evolution of isolated neutron stars is studied for a broad set of hyperonic EOSs. We use a multidomain 2-D code based on a spectral method, and show how important the precision of solving the equations of stationary motion is for the stability analysis. For some EOSs, the hyperon softening leads to spin-up by angular momentum loss, in the form of the back-bending phenomenon, for a rather broad range of stellar baryon mass. We show that large segments of the evolutionary tracks exhibiting the back-bending behaviour in the moment-of-inertia - rotation-frequency plane are unstable and therefore not astrophysically relevant. We show also that during the spin-up - angular-momentum-loss epoch, an isolated neutron star (e.g. a radio pulsar) can lose a sizable part of its initial angular momentum without significantly changing its rotation period. We propose also simple arguments and criteria allowing one to connect the presence of a back-bending epoch with the mass-radius relations and the stiffness and/or softness of the nucleon and hyperon EOSs of the neutron star core.


Key words: dense matter -- equation of state -- stars: neutron -- stars: rotation

Offprint request: J. L. Zdunik, jlz@camk.edu.pl




© ESO 2004