Journal Article

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 and P. Roche

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 422, issue 1, pages 199-206
Published in print May 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI:
The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657−415*

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We report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657−415 obtained in the H band using ISAAC on the Very Large Telescope.

Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s−1. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M and a mass of 14.3 ± 0.8 M for the Ofpe/WN9 highly evolved donor star.

OAO 1657−415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657−415 becomes the ninth with a dynamically determined NS 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 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 OAO 1657−415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657−415 current orbital configuration.

Keywords: binaries: eclipsing; binaries: general; stars: individual: OAO 1657−415; stars: massive; stars: Wolf–Rayet; X-rays: binaries

Journal Article.  6078 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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