Spectral classification of the mass donors in the high-mass X-ray binaries EXO 1722-363 and OAO 1657-415

A. B. Mason; J. S. Clark; A. J. NortonI. NegueruelaP. Roche

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Spectral classification of the mass donors in the high-mass X-ray binaries EXO 1722-363 and OAO 1657-415

机译：Spectral classification of the mass donors in the high-mass X-ray binaries EXO 1722-363 and OAO 1657-415

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Aims. We report near-infrared (NIR) observations of the mass donors of the eclipsing high-mass X-ray binary (HMXB) systems EXO 1722-363 and OAO 1657-415 in order to derive their accurate spectral classifications.Methods. ESO/VLT observations of the targets with the NIR spectrometer ISAAC were compared with several published NIR spectral atlases of O and B supergiants, an identification of each object's spectral characteristics was made, enabling the refinement of spectral classification of the mass donors.Results. We determined that EXO 1722-363 was of spectral type B0–B1Ia, positioned at a distance 8.0_(2.0)~(+2.5) kpc with a progenitor mass in the range 30-40 M_⊙ . Luminosity calculations imply that L_X~ 10~(35)-10~(37) erg s~(-1) for this distance range. We conclude that EXO 1722-363 shares many of the properties associated with other X-ray binary B-type supergiant donors.We found that OAO 1657-415 correlates closely with the spectra of a class of transitional objects, the Ofpe/WNL stars, an intermediate evolutionary stage between massive O type stars leaving the main sequence and evolving into Wolf-Rayets. Due to the wide range in luminosity displayed by Ofpe/WNL stars, (log(L/L_⊙ ) ~ 5.3-6.2) distance determinations are problematic. For OAO 1657-415 we report a distance of 4.4 ≤d ≤ 12 kpc, implying an X-ray luminosity of 1.5 x 10~(36) ≤ L_X ≤ 10~(37) erg s~(-1) . We have used our new classification of OAO 1657-415 to explain the physical processes responsible for its unique position within the Corbet diagram. Ofpe/WNL stars demonstrate a high rate of mass-loss through a dense stellar wind combined with a low terminal velocity. This combination of wind properties leads to a high accretion rate and transfer of angular momentum to the neutron star in this system. We believe this in turn leads to a smaller instantaneous equilibrium spin period with respect to normal OB supergiants.

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《Astronomy and astrophysics》 |2009年第1期|281-286|共6页
作者
A. B. Mason; J. S. Clark; A. J. NortonI. NegueruelaP. Roche;
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作者单位

Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK;

Departamento de Fisica, Ingenieria de Sistemas y Teoria de la Senal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain;

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正文语种英语
中图分类天文学;
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binaries; eclipsing – binaries; general – X-rays; binaries – stars; winds; outflows – stars; individual; OAO 1657-415 –stars; EXO 1722-363;

Spectral classification of the mass donors in the high-mass X-ray binaries EXO 1722-363 and OAO 1657-415

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