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Astron. Astrophys. 321, 591-604 (1997)

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Impact of medium effects on the cooling of non-superfluid and superfluid neutron stars

Ch. Schaab 1, D. Voskresensky 2, 3, A.D. Sedrakian 4, F. Weber 1, 5 and M.K. Weigel 1

1 Institute for Theoretical Physics, Ludwig-Maximilians Universität, Theresienstrasse 37/III, D-80333 Munich, Germany
2 Gesellschaft für Schwerionenforschung GSI, P.O. Box 110552, D-64220 Darmstadt, Germany
3 Moscow Institute for Physics and Engineering, 115409 Moscow, Kashirskoe shosse 31, Russia
4 Max-Planck-Society, Research unit 'Theoretical Many-Particle Physics' at Rostock University, Universitätplatz 1, D-18051 Rostock, Germany
5 Nuclear Science Division, Lawrence Berkeley National Laboratory, MS: 70A-3307, University of California, Berkeley, CA 94720, USA

Received 24 June 1996 / Accepted 24 October 1996

Abstract

Neutrino emission from the dense hadronic component in neutron stars is subject to strong modifications due to collective effects in the nuclear medium. We implement new estimates of the neutrino emissivities of two processes operating in the nuclear medium into numerical cooling simulations of neutron stars. The first process is the modified Urca process, for which the softening of the pion exchange mode and other polarization effects as well as the neutrino emission arising from the intermediate reaction states are taken into account. The second process concerns neutrino emission through superfluid pair breaking and formation processes. It is found that the medium effects on the emissivity of the modified Urca process result in a strong density dependence, which gives a smooth crossover from the standard to the nonstandard cooling scenario for increasing star masses. For superfluid stars, the superfluid pair breaking and formation processes accelerate mildly both the standard and the nonstandard cooling scenario. This leads to a good agreement between the theoretical cooling tracks and the rather low temperatures observed for objects like PSRs 0833-45 (Vela), 0656+14, and 0630+18 (Geminga). The robustness of our findings against variations in both the underlying equation of state of baryonic matter and the used fast cooling processes is demonstrated. Hence we conclude that the two recalculated neutrino emissivities studied here enable one to reproduce theoretically most of the observed pulsar temperatures by varying the masses of neutron star models.

Key words: stars: neutron – stars: evolution – dense matter – X-rays: stars

Send offprint requests to: Ch. Schaab, email: schaab@gsm.sue.physik.uni-muenchen.de

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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