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Astron. Astrophys. 340, 85-102 (1998)


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High-eccentric X-ray binaries: evolution, wind rose effect, accretor-propeller luminosity gap

Natalya V. Raguzova 1, 2 and Vladimir M. Lipunov 1, 2

1 Faculty of Physics, Moscow University, 117234 Moscow, Russia
2 Sternberg Astronomical Institute, Moscow University, 119899 Moscow, Russia (e-mail: raguzova@sai.msu.su, lipunov@sai.msu.su)

Received 11 May 1998 / Accepted 10 July 1998

Abstract

The influence of the spatial distribution of stellar wind velocities (Wind Rose effect) on the X-ray light curve of highly eccentric binaries is examined using the properties of spherical-symmetrical and Be disk-fed outflow. The effects of the wind geometry, velocities and densities in the stellar wind of the Be star and of the orbital motion of the neutron star on the expected X-ray luminosity are investigated. It is shown that the shapes of the X-ray light curves depend strongly on the outflow velocity of the gas ejected by the Be star at the orbital distance of the compact object. If [FORMULA] then the X-ray luminosity is high and the X-ray light curves are determined by the orbital velocity of the neutron star. The effects of changes in the mass loss rate of the Be star and in the orbital separation on the expected X-ray light curves are studied. It is shown that a phase shift of the maximum X-ray luminosity is always present in the X-ray light curves. We show that in some cases an accretion disk may temporarily form around the neutron star. The observed X-ray light curves of some transient binaries are analysed using the developed model. We show that the Be/X-ray transients A 0538-66, X 0331+53 and some other sources are likely to undergo transitions from the accreting neutron star regime to the propelling one. Evolutionary scenarios which can lead to a formation of the binary systems A 0538-66, A 0535+26, X 0331+53, 4U 1145-619, 4U 0115+634 and EXO 2030+375 are presented. For the first time, the evolutionary tracks include both the orbital period changes and the neutron star spin period history. Using Monte Carlo simulations, we calculate the number distributions of Be+X-ray PSR binaries over orbital periods and eccentricities for different scenario parameters taking into consideration the influence of kick velocity and synchronization. We conclude that synchronization is a very important process and must be taken into account when calculating Be star evolution in binary systems. We also calculate the critical orbital period for existence of a Be+X-ray pulsar binary, which is [FORMULA]. The obtained distributions is in good agreement with the observational lack of such binaries with orbital period [FORMULA].

Key words: stars: binaries: close – stars: evolution – stars: mass-loss – X-rays: stars

Send offprint requests to: N. Raguzova

© European Southern Observatory (ESO) 1998

Online publication: November 3, 1998

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