Volume 606, October 2017
|Number of page(s)||7|
|Section||Stellar structure and evolution|
|Published online||10 October 2017|
Formation of Scorpius X-1 induced by anomalous magnetic braking of Ap/Bp stars
1 School of Physics and Electrical Information, Shangqiu Normal University, Shangqiu 476000, PR China
2 Department of Physics, University of Oxford, Oxford OX1 3RH, UK
3 Argelander-Insitut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Received: 13 December 2016
Accepted: 15 August 2017
Sco X-1 is the brightest persistent X-ray source in the sky. It is generally believed that Sco X-1 is a low-mass X-ray binary containing a neutron star that accretes from a low-mass donor star where the mass transfer is driven by magnetic braking. However, the mass transfer rate predicted by the standard magnetic braking model is at least one order of magnitude lower than the rate inferred by X-ray luminosity. In this work, we investigate whether this source could have evolved from an intermediate-mass X-ray binary including Ap/Bp stars with a slightly strong magnetic field of 300–1000 G. The coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accretor can yield strong magnetic braking that could give rise to a relatively high mass transfer rate. According to the observed orbital period, the mass transfer rate, the mass ratio, and the donor star spectral type, the progenitor of Sco X-1 should be an intermediate-mass X-ray binary including a 1.6−1.8 M⊙ Ap/Bp donor star in a 1.3−1.5 day orbit. We therefore propose that anomalous magnetic braking of Ap/Bp stars provides an alternative evolutionary channel to some of the luminous X-ray sources.
Key words: X-rays: individuals: Sco X-1 / X-rays: binaries / stars: mass-loss / stars: winds, outflows / stars: evolution
© ESO, 2017
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