On the rapid orbital expansion in the compact low-mass X-ray binary 2A 1822$-$371. (arXiv:1911.06945v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Xing_Z/0/1/0/all/0/1">Ze-Pei Xing</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_X/0/1/0/all/0/1">Xiang-Dong Li</a> (NJU)
The neutron star low-mass X-ray binary 2A 1822$-$371 has an orbital period of
5.57 hr. Mass transfer in such short-period binaries is thought to be driven by
magnetic braking with orbital shrinking. However, 2A 1822$-$371 shows a very
rapid orbital expansion, implying that mass transfer occurs rapidly in this
system. The accretion rate of the neutron star is observationally estimated to
be higher than the Eddington limit, which is also hard to be explained by the
standard magnetic braking mechanism. In this work, we construct a model to
account for the peculiar properties of 2A 1822$-$371. We assume that the donor
star possesses a relatively strong magnetic field, which is coupled with the
stellar winds excited by the X-ray radiation from the neutron star. This would
generate efficient angular momentum loss, leading to a high mass transfer rate
and hence orbital expansion. We provide possible evolutionary tracks of 2A
1822$-$371 and study how the input parameters affect the results. The
observational implications of the irradiation-driven mass loss are also briefly
discussed in the context of evolution of low-mass X-ray binaries and
millisecond pulsars.
The neutron star low-mass X-ray binary 2A 1822$-$371 has an orbital period of
5.57 hr. Mass transfer in such short-period binaries is thought to be driven by
magnetic braking with orbital shrinking. However, 2A 1822$-$371 shows a very
rapid orbital expansion, implying that mass transfer occurs rapidly in this
system. The accretion rate of the neutron star is observationally estimated to
be higher than the Eddington limit, which is also hard to be explained by the
standard magnetic braking mechanism. In this work, we construct a model to
account for the peculiar properties of 2A 1822$-$371. We assume that the donor
star possesses a relatively strong magnetic field, which is coupled with the
stellar winds excited by the X-ray radiation from the neutron star. This would
generate efficient angular momentum loss, leading to a high mass transfer rate
and hence orbital expansion. We provide possible evolutionary tracks of 2A
1822$-$371 and study how the input parameters affect the results. The
observational implications of the irradiation-driven mass loss are also briefly
discussed in the context of evolution of low-mass X-ray binaries and
millisecond pulsars.
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