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WRAY 977 (GX301-2): A HYPERGIANT WITH PULSAR COMPANION

L. Kaper·H. J. G. L. M. Lamers·E. Ruymaekers·E. P. J. van den Heuvel·E. J. Zuiderwijk
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Abstract

Wray 977, the B supergiant companion of the X-ray pulsar GX301-2, should be classified as B1~Ia+, based on a comparison of its optical spectrum to that of zeta1 Sco, a well-known B hypergiant and ONE OF THE BRIGHTEST STARS IN THE GALAXY. The classification of Wray 977 as a hypergiant results in a new distance determination of the binary system, i.e. 5.3 kpc (previously 1.8 +/- 0.4 kpc). The ``average'' X-ray luminosity of the pulsar is then ~10^37 erg/s, in good agreement with the predicted X-ray luminosity resulting from accretion of a dense, low-velocity (v_infty = 400 km/s) stellar wind. A mass-loss rate of <= 10^-5 M_sun/yr is estimated from the Halpha profile. A new upper limit for the inclination of the system is derived which provides a lower limit to the (present) mass of Wray 977 (48 M_sun). Regarding current binary evolution scenarios, the empirical lower mass limit for BLACK-HOLE formation in a binary increases to M_zams >= 50 M_sun.

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L. Kaper, H. J. G. L. M. Lamers, E. Ruymaekers, E. P. J. van den Heuvel, E. J. Zuiderwijk. 1995-03-01. WRAY 977 (GX301-2): A HYPERGIANT WITH PULSAR COMPANION. https://arxiv.org/abs/astro-ph/9503003

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