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arXiv · 1102.3363

The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657-415

A. B. Mason·J. S. Clark·A. J. Norton·P. A. Crowther·T. M. Tauris·N. Langer·I. Negueruela·P. Roche
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Abstract

We report near-infrared radial velocity measurements of the recently identified donor star in the high mass X-ray binary system OAO 1657-415 obtained in the H band using ISAAC on the VLT. Cross-correlation methods were employed to construct a radial velocity curve with a semi-amplitude of $22.1 \pm 3.5$ km s$^{-1}$. Combined with other measured parameters of this system this provides a dynamically determined neutron star mass of $1.42 \pm 0.26 M$_{\odot}$ and a mass of $14.3 \pm 0.8 M$_{\odot}$ for the Ofpe/WN9 highly evolved donor star. OAO 1657-415 is an eclipsing High Mass X-ray binary pulsar with the largest eccentricity and orbital period of any within its class. Of the ten known eclipsing X-ray binary pulsars OAO 1657-415 becomes the ninth with a dynamically determined neutron star mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657-415 is much more highly evolved than the majority of the supergiant donors in other High Mass X-ray binaries (HMXBs), joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres. Considering the evolutionary development of OAO 1657-415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor's envelope via spiral-in, ruling out a Common Envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO1657-415 remains problematic, we conclude by proposing two scenarios which may account for OAO1657-415 current orbital configuration.

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A. B. Mason, J. S. Clark, A. J. Norton, P. A. Crowther, T. M. Tauris, N. Langer, I. Negueruela, P. Roche. 2012-01-20. The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657-415. https://doi.org/10.1111/j.1365-2966.2012.20596.x

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