Formation of Scorpius X-1 induced by anomalous magnetic braking of Ap/Bp stars

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 sta...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2017-10, Vol.606, p.A60
Main Author: Chen, Wen-Cong
Format: Article
Language:English
Subjects:
A stars
B stars
Binary stars
Braking
Irradiation
Luminosity
Magnetic fields
Mass transfer
Neutron flux
Orbits
outflows
Peculiar stars
Product development
stars: evolution
stars: mass-loss
stars: winds
Stellar evolution
Stellar magnetic fields
Stellar winds
X ray binaries
X ray sources
X ray stars
X-rays: binaries
X-rays: individuals: Sco X-1
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Summary: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.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201630239